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Systematic Review
Revised

SARS-CoV-2 and the role of airborne transmission: a systematic review

[version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]
PUBLISHED 19 Oct 2022
Author details Author details
OPEN PEER REVIEW
REVIEWER STATUS

This article is included in the Emerging Diseases and Outbreaks gateway.

This article is included in the Pathogens gateway.

This article is included in the Coronavirus (COVID-19) collection.

Abstract

Background: Airborne transmission is the spread of an infectious agent caused by the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in the air. We carried out a systematic review to identify, appraise and summarise the evidence from studies of the role of airborne transmission of SARS-CoV-2.
Methods: We searched LitCovid, MedRxiv, Google Scholar and the WHO Covid-19 database from 1 February 2020 to 30 May 2022 and included studies on airborne transmission. Data were dual extracted, and we assessed quality using a modified QUADAS 2 risk of bias tool.
Results: We included 128 primary studies and 29 reviews on airborne SARS-CoV-2. Of the 128 primary studies, 105 (82%) reported data on RT-PCR from air samples, 28 (22%) report cycle threshold values and 36 (28%) copies per sample volume. All primary studies were observational. The research often lacked standard methods, standard sampling sizes and reporting items. We found 69 descriptions of different air samplers deployed. Of the 80 in-hospital studies that reported binary RT-PCR tests, 362/3079 air samples from 75 studies conducted in hospital ward environments were positive (median 8%, IQR=0 to 23%); 23 studies reported 74/703 RT-PCR positive air samples in the ICU setting (median 17%, IQR=0% to 38%) Thirty-eight studies reported potential air transmission in the outdoors or in the community. Twenty-six studies attempted viral culture, none of which definitively demonstrated that replication-competent SARS-CoV-2 could be recovered in the air.
Conclusion:  SARS-CoV-2 RNA is detectable intermittently in the air in various settings. Standardized guidelines for conducting and reporting research on airborne transmission are needed. The lack of recoverable viral culture of SARS-CoV-2 from air samples prevents firm conclusions about the definitive role of airborne transmission in SARS-CoV-2.

Keywords

SARs-CoV-2, transmission, COVID, Airborne

Revised Amendments from Version 2

We have updated the review to 30 May 2022. Data were dual extracted, and we assessed quality using a modified QUADAS 2 risk of bias tool. The results now include 128 primary studies and 29 reviews on airborne SARS-CoV-2, and 26 studies attempting viral culture. As a post-hoc analysis, we have also compared the positivity rates of PCR air samples for studies that reported both ICU and non-ICU sample positivity estimates. We have updated the tables and figures with the new studies and added in a meta-analysis of the ICU and non-ICU PCR samples. We have also added further information to the viral culture methodological issues. We have added Jason Oke to the author list for his methodological expertise in this new version.

See the authors' detailed response to the review by Nancy H. L. Leung
See the authors' detailed response to the review by Maosheng Yao
See the authors' detailed response to the review by David R. Tomlinson

Introduction

Airborne transmission is defined as the spread of an infectious agent caused by the dissemination of droplet nuclei (aerosols) that remain infectious when suspended in air over long distances and time1. There are varied definitions of aerosols in the published literature. An aerosol is defined as a collection of particles (liquid or solid) with varying aerodynamic diameters, suspended in the air (gas) for a prolonged time period. The size of the particles and the distance travelled is highly variable and depends on multiple factors including the force generated at the source from which the particles originate, the relative humidity, evaporation level, settling velocity, direction of airflow, the number of air changes per hour, temperature, crowding and other environmental factors25. Droplet nuclei are airborne residue (with or without embedded pathogens) of a respiratory droplet containing non-volatile solutes, from which water has evaporated to the point of equilibrium with the ambient relative humidity6.

Transmission via droplet nuclei and aerosols in specific settings or situations may potentiate the spread of some viruses in humans, resulting in disease outbreaks that are difficult to manage. The results of several studies investigating airborne human-to-human virus transmission have been largely inconclusive7,8. Among case reports and case clusters for which airborne transmission is hypothesised, published details of the investigations cannot definitively rule out droplet and/or fomite transmission that could also explain human-to-human transmission9. Therefore, we aimed to systematically review the airborne transmission evidence for SARS-CoV-2.

Methods

We are undertaking a series of systematic reviews investigating factors and circumstances that impact the transmission of SARS-CoV-2, based on our published protocol last updated Version 4: 1 June 2022) (archived protocol: Extended data: Appendix 110) Briefly, this review is the third updated version that aims to identify, appraise, and summarize the evidence (from studies peer-reviewed or awaiting peer review) relating to the role of airborne transmission of SARS-CoV-2 and the factors influencing transmissibility.

We searched four main databases: LitCovid, medRxiv, Google Scholar and the WHO Covid-19 database for COVID-19 using the terms Airborne: aerosol OR airborne OR airbourne OR inhalation OR air OR droplet initially from 1 February 2020 up to 20 December 2020; the searches were updated for version 3 to 30 May 2022 (see Extended data: Appendix 2 for the search strategies10). We aimed to include studies that sampled the air for the detection of SARS-CoV-2 in the populations under study or the environment. We primarily included studies that reported sampling for the detection of SARS-CoV-2. However, we also included observational and randomised studies that investigated airborne transmission of SARS-CoV-2. Non-predictive and experimental studies were also considered for inclusion. Studies should include air sampling for the detection of SARS-CoV-2. Studies incorporating models to describe observed data were eligible, but studies reporting solely predictive modelling were excluded. For relevant articles citation tracking was undertaken. We searched the included primary studies of all retrieved reviews and included them in the results section for reference.

We included field studies that included airborne sampling for SARS-CoV-2 in the population under study or the environment. JB performed the searches, TJ and EAS performed the first screen and CJH checked the initial screening of these studies. Three reviewers (EAS, CJH, TJ) extracted data for each study, and the data was independently checked. We extracted information on the study characteristics, the study population, setting and methods, and the main results from included studies. We also extracted data on the type of study, setting, sample source and methods, RT-PCR positive samples for SARS-CoV-2 RNA including cycle threshold (Ct) and copies per m3 of sampled air, viral culture methods and results, size of air particles (when reported) and proportion in the sample. We tabulated the data and summarised the data narratively by sample type. We assessed quality using a modified QUADAS 2 risk of bias tool11. We simplified the tool because the included studies were not primarily reported as diagnostic accuracy studies. Furthermore, there is a lack of high-quality data in published transmission studies12. We gave particular importance to the description of methods for air sampling and the reporting of sufficient detail to enable replication of the study by other investigators. We examined the following domains: (i) source population – did the study authors adequately describe the source population? e.g., setting, time since symptom onset, presence and degree of symptoms including presence of cough or sneezing, any treatments employed, presence of other mitigating factors, severity of SARS-CoV-2, baseline demographics including concurrent respiratory infections or other comorbidities, distance between study subjects; (ii) methods – did the study authors sufficiently describe the methods used to enable replication of the study? e.g., methods used for diagnosing SARS-CoV-2 in patients, the procedure used for air sampling, time-point for sampling, number of samples per site, cycle threshold determination, culture methods, verification methods to confirm the presence of SARS-CoV-2, airflow/ventilation settings, humidity and any other mitigating environmental circumstances; (iii) sample sources – did the authors clearly describe the sources for the air samples? What was the volume of air in each sample? Was the period of sampling similar across various sites? (iv) outcome reporting – was the reporting of the results consistent with the study outcomes and was the analysis of the results appropriate – e.g., interval and time-point for testing study participants for potential transmission. The risk of bias for each domain was rated “low”, “moderate” or “high” depending on the adequacy of reporting. One reviewer (EAS) assessed the risk of bias while a second author (CJH) independently verified the risk of bias. Any disagreements were resolved through discussion. Where a consensus could not be reached, a third reviewer (IJO) arbitrated. We summarise data narratively and report the outcomes as stated in the paper, including quantitative estimates when reported and the detection of the culture of SARS-CoV-2, including quantitation, whenever available.

As a post-hoc analysis, we compared the positivity rates of PCR air samples for studies that reported both ICU and non-ICU sample positivity estimates. Using a random-effects model with inverse variance weighted meta-analysis, the difference in positivity rates was computed as odds ratios (OR) with 95% confidence intervals (CI). A statistician (JO) performed the analysis independently before seeing the study data. In a sensitivity analysis, a continuity correction was applied to studies (n=4) where neither arm reported a positive sample.

Results

From 1,001 records screened, we identified 240 eligible studies (see Figure 1; 83 full-text studies were excluded because they were not reviews or there was no SARS-CoV-2 airborne transmission outcome studied, and we excluded four laboratory studies (see Extended data: Appendix 3 for a list of excluded studies10). We included 128 primary studies and 29 reviews (see Extended data: Appendix 3 for references to included studies and Table 1 and Table 2 for the characteristics of the included studies10).

9ad1e537-1b7b-4130-8ba5-352576faa348_figure1.gif

Figure 1. Flow Chart for Airborne Transmission.

Table 1. Study characteristics: primary studies.

SettingCountryMethodSamples SourceAir Samples
PCR positive
for SARs-CoV-2
RNA (unless
otherwise
stated)
Viral culture
Adenaiye OO
2021
University
campus and
community
USACOVID-19 cases series. Fomite
(phone) swabs, and 30-minute
exhaled breath samples
30-minute breath samples while vocalizing into a
Gesundheit-II, 2 paired breath samples 1 with and 1
without a mask; 1 or 2 visits 2 days apart.
No mask
coarse = 15/78
fine = 22/78
With mask
coarse = 10/71
fIne = 14/71
All positive aerosol
samples were
negative after
three passages
of Vero-E6 cells
inoculated in a
blind test.
Ahn JY 2020HospitalChinaAir (and surface) samples collected.
Virus culture was attempted on PCR
positive samples.
Air sampling at 1.2 m above floor level, 1.0 m from each
patient, using an SKC BioSampler and a Swab sampler.
0/ (denominator
unclear)
samples
Not attempted.
Alkalamouni H
2021
HospitalLebanonAir samples over 2 consecutive
days in the COVID-19 unit hallway,
near the staff station, and in patient
rooms.
Air samples were collected inside the ED COVID-19
unit using the Coriolis µ microbial air sampler (Bertin
Technologies) at a flow rate of 200 L/min for 20 min over
two consecutive days.
0/13Not attempted.
Ang AX 2021HospitalSingaporeAir and surface samples were
collected from one isolation ward
and two open-cohort wards housing
laboratory-confirmed COVID-19
patients
Air sampling was conducted with filter-based SASS
3100 air samplers (Research International). The sampler
collects total suspended particle (TSP) with no particle size
cutoff. The filter media were the default 44 mm diameter
SASS bioaerosol filter (polyester material, no electrostatic
charge, Research International) with two different pore-
sizes.
13/270/27
Baboli 2021HospitalIran Passive and active sampling
methods were employed and
compared with regard to their
efficiency for collection of airborne
SARS-COV-2 virus particles.
Fifty one indoor air samples were collected in two areas,
with distances of less than or equal to 1 m (patient room)
and more than 3 m away (hallway and nurse station) from
patient beds.
6/51Not attempted.
Baribieri P
2021
Hospital Italy Five 24-h PM10 samples in a
COVID-19 geriatric ward in late June
2020,
PM10 collected by a low noise (<35 dB) air sampler
(SILENT Air Sampler—FAI Instruments S.r.l., Roma, Italy)
for 24 h on quartz fiber filters (prefired 47 mm diameter
Pallflex, Pall Corporation, Port Washington, New York) with
single sampling head operating at a flow rate of 10 L/min
with a relative uncertainty of 5% of the measured value.
One PM sample (24 h for a total of 14.4 m3 of air) was
collected every day.
10/20patient swabs
cultured*
Barksdale AN
2020
HospitalUSA four air samples were taken in
the ED to evaluate SARS-CoV-2
contamination levels
Stationary air samples were collected using a Sartorius
Airport MD8 air sampler operating at 30 liters per minute
for 30 minutes onto an 80mm gelatin filter.
1–9Not attempted.
Bays D 2020Healthcare
setting
USATwo detailed case studiesNo sampling performedNot attempted.N/A
Bazzazpour S
2021
Dental clinicsIran 36 air samples at dental clinics Air sampling was done (n = 36) collecting particulate
samples on PTFE filters at flow rates of 30 to 58 L/min.
13/36Not attempted.
Ben-Shmuel
2020
hospital &
quarantine hotel.
Israel Surface and air sampling were
conducted at two COVID-19
isolation units and in a quarantine
hotel.
Air sampling was performed using an MD8 air sampler
(Sartorius, Göttingen, Germany) equipped with gelatine
membranes (3.0 μm filtration cut-off) at 50 L/min
sampling rate for 20 min.
2/6
quarantine
hotel 1/1
0/3
Binder 2020HospitalUSACase series of 20 patients
hospitalized with coronavirus
disease
8 National Institute for Occupational Safety and Health
(NIOSH) BC 251 Aerosol Samplers (Figure S3) were placed
1.5m from the ground, at ~1 meter, ~1.4 meters, ~2.2
meters, and ~3.2 meters from the SARS-CoV-2 patient’s
head and subsequently run for ~4 hours. 195 air samples
were collected
3/195 samples
from 3 patients
0/3 viable virus
Bokharaei-
Salim F 2021.
hospitalIran two air sampling strategies. used
simultaneously in three hospital
wards
Liquid impaction, an impinger with a standard nozzle was
employed to capture virus aerosols in a collecting liquid.
Sampling was performed on the 5 mL of DMEM media
Air samples were prepared by the flow rate of 1.5 L/min
for 180 min. In the filtration view, polytetrafluoroethylene
filters by diameter of 25 mm and 0.4 µm porosity (SKC Inc)
were used in the 25 mm 2-piece cassettes of clear styrene
(SKC Inc)
Liquid
impaction 0/7
Filtration 0/7
Not attempted.
Cai Y 2020Hospital ChinaAir samples and 128 environmental
surface swabs were collected from
14 patients in 4 departments with
temporary COVID-19 ICU wards.
Sample collegted using a dry-filter air sampler (52-mm
electret filters, InnovaPrep ACD-200 Bobcat, America)
operating at a speed of 20048L/min for 60 minutes in
the 14 temporary ICU wards. The filters were eluted in
7-mL elution fluid (comprising water, a low-concentration
surfactant [0.075%49Tween 20], and a pH buffer [20mM
Tris (hydroxymethyl) aminomethane or phosphate-
buffered saline]; InnovaPrep, America), which was mixed
with viral50transport medium (sterile Hank’s fluid.
0/15N/A
Charlotte N
2020
Choir practiceFranceFollow-up of a choir practice: 27
participants, including 25 male
singers, a conductor and an
accompanist attended a choir
practice on 12 March 2020.
No sampling performedNot attempted.Not attempted.
Cheng VCC
2020a
HospitalChinaAir sampling: 6 patients’ air sampled,
and 5 positive controls
The air sampler was perpendicularly positioned 10 cm
away from the patient’s chin, collecting at a rate of
50 L/minute. An air tent was used to increase the
proportion of exhaled air collected. Participants sneezed
directly onto gelatin filter and spit saliva droplets onto
gelatin filter.
0/6 Not attempted.
Cheng VCC
2020b
HospitalChina Air sampling using ISO 180 model
86834 air sampler was performed in
the room of a patient.
Air samples were collected 10 cm from the one patient’s
chin. The patient performed 4 different manoeuvres
(normal breathing, deep breathing, speaking “1, 2, 3”
continuously, and coughing continuously) while putting
on and removing the surgical mask.
0/8 Not attempted.
Cheng VCC
2021
Hospital Chinaenvironmental samplings, and
whole-genome sequencing (WGS)
were performed for a hospital
outbreak.
Swab samples from the patients’ bedside environments
and air grilles (10 cm × 120 cm in size at the ceiling height
of 2.35 m in the corridor and 2.6 m in the cubicle) of the
air ventilation system in ward 2D were taken for SARS-
CoV-2 using RT-PCR testing before and after terminal
disinfection
8/22 air grilles Not attempted.
Chia PY 2020HospitalSingaporeAir (and surface) sampling
surrounding 61 hospitalized
COVID-19 patients in airborne
infection isolation rooms
Air sampling was performed in three of the 27 airborne
infection isolation rooms (AIIRs). Bioaerosol samplers
used to collect air samples, set at a flow-rate of 3.5 L/min
and run for four hours, collecting a total of 5,040 L of air
from each patient’s room.
2/3 air samplesNot attempted.
Chirizzi D
2020
OutdoorItalyStudy of the outdoor concentrations
and size distributions of virus-laden
aerosol simultaneously collected, in
May 2020, in northern (Veneto) and
southern (Apulia) regions of Italy.
Genetic material of SARS-CoV-2 (RNA) was determined,
using both real time RT-PCR and ddPCR, in air samples
collected using PM10 samplers and cascade impactors
able to separate 12 size ranges from nanoparticles
(diameter D < 0.056 µm) up to coarse particles (D > 18
µm).
Outdoor
atmospheric
concentrations
of SARS-CoV-2
were very small
(<0.8 copies
m−3)
Not attempted.
Coleman KK
2021
Hospital SingaporeExhaled breath emitted by
COVID-19 patients
Used a G-II exhaled breath collector, to measure viral RNA
in coarse and fine respiratory aerosols emitted by
COVID-19 patients during 30 minutes of breathing, 15
minutes of talking, and 15 minutes of singing. participants
were seated facing the truncated cone-shaped inlet,
with air drawn continuously (130 L/minute) around the
subject’s head and into the sampler. Aerosols were
collected in 2 size fractions, namely coarse (>5 μm) and
fine (≤ 5μm).

25/66 samples

0/25 samples
Conte M 2021Indoor
Community
Italy air samples collected in different
community indoors
(one train station, two food markets, one canteen, one
shopping centre, one hair salon, and one pharmacy) in
three Italian cities: metropolitan city of Venice (NE of Italy),
Bologna (central Italy), and Lecce (SE of Italy). Air samples
were collected using quartz fibre filters with low-volume
samplers
0/7N/A
Declementi M
2020
HospitalItaly Air sampling to assess
environmental contamination in
a COVID-19 non-Intensive Care
Unit. Two patients admitted to the
hospital rooms were positive for
COVID-19 for more than a week.
8 air samples were collected before and after the
application of two different sanitization devices. Pumps
were placed in 4 sites: patient 1 room, patient 2 room, an
empty room nearby patients’ rooms, corridor outside the
rooms. Pumps (47 mm filter cassettes and 0.45 μm filters
in polytetrafluoroethylene-PTFE) positioned 1 meter above
the floor for 340 minutes at 15 l/min.
0/8 Not attempted.
De Man P
2020
Care homeThe
Netherlands
Case series. Responding to an
outbreak in a care home, the
ventilation system of the outbreak
ward was investigated in addition to
routine source and contact tracing
No air samples collected.Not attempted.N/A
Di Carlo P
2020
Inside a busItalyObservational measurements
were carried out across the last
week of the lockdown and the first
week when, gradually, all travel
restrictions were removed. 12 to 22
May 2020 in Chieti, Italy.
Samples of air inside the bus were taken every day of
the two observational weeks, excluding weekends. Two
microbiological gelatine membrane sample filters of 80
mm diameter were installed on board: one close to the
ticket machine, the other on the rear part of the bus. All
the air samples were gathered during the 6.5 hours daily
operation of the bus,
0/14 Not attempted.
de Rooij MMT
2021
Meat processing
plant
HollandSARS-CoV-2 screening of workers
operating in cooled production
rooms and intensive environmental
sampling
Stationary air sampling was performed at potential
hotspots based on workers’ density and ventilation
characteristics in both production rooms. a filter-based
technique was used to sample inhalable dust—airborne
particles small enough to enter the respiratory tract.
1–12Not attempted.
Ding Z 2020HospitalChinaSampling, including of air, within
and around 4 isolation rooms each
with 3 patients. Other areas in the
hospital and its roof air-exhausts
were also sampled.
46 air samples, two exhaled condensate samples, and
two expired air samples (also 47 surface samples) were
collected within and beyond the 4 three-bed isolation
rooms.
1/46 air
samples
weakly positive.
Both exhaled
condensate
samples
negative.
Both expired
air samples
negative.
Not attempted.
Dohla M 2020Quarantined
households
GermanyStudy of 43 adults and 15 children
living in 21 households; air (also
surface and wastewater) samples
taken.
Air samples obtained using Coriolis Micro-Air sampler; air
collectors were positioned in the middle of the room used
most frequently by the residents (usually the living room
or kitchen) - no rooms had ventilation equipment. Close
contact to the air sampler was avoided (e.g. speaking in a
range below 2 m but not above 3 m).
0/15 Infectious virus
could not be
isolated in Vero
E6 cells from any
environmental
sample.
Dubey A 2021HospitalIndia portable air sampling from the
medicine ward, intensive care unit,
and emergency ward admitting
COVID-19 patients.
Total suspended particulate (TSP) air sampler, (M/s.
Vayuvodhan, Okhla Industrial Area, New Delhi) which was
calibrated as per national standards by CSIR-NPL, India
was used for collecting suspended particulate matter
from the air.
medicine ward
1m. 6/6; 3m 2/6
ICU
1m. 6/6; 3m 3/6
EmWard
5/6
Nursing station
(glass wall) 0/6
Nursing station
area ICU (glass
wall) 0/6
Not attempted.
Dumont-
Leblond N
2020
HospitalCanadaAir sampling in acute care hospital
rooms over the course of nearly two
months
100 air samples in acute care hospital rooms hosting 22
patients using three different air sampling protocols. Two
conductive plastic Institute of Occupational Medicine
(IOM) samplers with 3 µm gelatine filters or one IOM and
a 37 mm cassette with 0.8 µm polycarbonate filters.
11/100 from 6
patient rooms
Viral cultures were
negative
Dumont-
Leblond N
2021
Long-term care
facilities
Canada Air and no-touch surfaces of 31
rooms from 7 LTCFs were sampled
Air sampling was performed using an IOM Multidust
sampler (SKC, Eighty Four, PA, USA) loaded with a
3 μm gelatin filter (Sartorius Stedim Biotech, Gottingen,
Germany).
0/7Not attempted.
Dziedzinska R
2021
public spacesCzech
Republic
Air and surface samples in a Post
Office and Shopping Centre
The air was sampled by the commercially available air
washer LW220 (Beurer, Ulm, Germany).
0/2Not attempted.
Escudero D
2021
Hospital Spainpresence of SARS-CoV-2 in the air
of two ICUs and in the pneumology
ward dedicated to the treatment of
patients with COVID-19.
The air samples were obtained using two different
methods: (1) SAS Bioser Mod. Microbio 0111302 sampling
equipment with an air flow of 500 l/300 s and a Rodac
plate measuring 55 mm in diameter from which samples
were subsequently obtained with pre-humidified swabs.
With this system the estimated volume of air passing
through the plate in one hour is 5,967 l; and (2) A filtration
ramp with a polyethersulfone membrane filter (FILTER-
LAB®) of pore size 0.1 μm and measuring 47 mm in
diameter, connected to the hospital vacuum system by
means of a 60 kPa vacuometer.
ICU 0/6
Ward 0/1
N/A
Faridi S 2020HospitalIranAir sampling in wards of Covid-19
patients with severe and critical
symptoms.
10 air samples were collected into the sterile standard
midget impingers containing 20 mL DMEM with 100
μg/mL streptomycin, 100 U/mL penicillin and 1% antifoam
reagent for 1 h. Air samplers placed 1.5 to 1.8 m above
the floor and approximately 2 to 5 m away from the
patients' beds. Some patients coughed during the sample
collection.
0/10 Not attempted.
Feng B 2020HospitalChinaEnvironmental contamination
investigated around 21 COVID-19
patients in the later stage of
infection
For sampling of isolation room air, a NIOSH sampler was
placed on a tripod 1.2 m in height and 0.2 m away from
the bed at the side of the patient’s head. The sampling
duration was 30 min, and a total of 105-L room air was
sampled. (9 Exhaled Breath (EB) samples, 8 Exhaled
Breath Condensate (EBC) samples, 12 bedside air
samples)
0/14 EB
2/8 EBC
1/12 room air
Not attempted.
Ge XY 2020HospitalChina Environmental; air samples from 6
different sites of 3 hospitals
Air samples were collected for 30 min using the National
Institute for Occupational Safety and Health (NIOSH)
bioaerosol sampler (BC251) with air pumps (XR5000, SKC).
The stream of air has been set to 3.5 L / minute.
ICU 3/3
Haemodyalysis
clinic 0/12
fever clinic 0/12
respiratory ward
0/6
Not attempted.
Ghaffari HR
2021
Hospital Iran indoor air samples of intensive care
unit (ICU) with confirmed COVID- 19
patients and its surroundings.
Detection of SARS-CoV-2 was conducted in the four
sections of ICU including the patient section, nurse
station, rest room, and doorway of ICU. The low volume
sampler (LVS) (ESPS Model, Fanpaya) was applied to
collect SARS-CO-2 virus bound to PM2.5 and PM10
2/16
ICU 2/8
Ward 0/8
Not attempted.
Gharehchahi E
2021
Hospital Iran Sampling of indoor air, on the
surfaces, and the fomites of a
COVID-19 referral hospital
Indoor air sampling was conducted utilizing a standard
midget impinger containing 15 ml of viral transfer
medium (VTM) equipped with a sampling pump with a
flow rate of 10 L min− 1 for 60 minutes.
Total 7/17
ICU 2/3
-ve pressure
room 1/1
A&E 1/4
Ward 0/4
CT scan 0/2
Offices 2/2
Laundry 0/1
Temp Waste
Storage 1/1
Not attempted.
Gholipour S
2021
Wastewater
treatment plant
Iran analyzed the presence of viral RNA
of SARS-CoV-2 in raw wastewater
and air samples of WWTPs
A total of 15 air samples were collected using all-glass
impingers, containing phosphate buffer solution. Air
sampling was performed at three sites in WWTP A,
including pumping station and activated sludge plants at
a height of 1.5 m above the ground level.
6/15Not attempted.
Gomes da
Silva P 2022
Hospital Portugal Air samplesf rom eleven different
areas of the Hospital (4 COVID-19
areas)
Two cyclonic microbial air samplers, a Coriolis® μ and
a Coriolis® Compact (Bertin Instruments, Montigny-
le-Bretonneux, France). Using the Coriolis® μ, three
consecutive air samplings were collected from each of
the eleven areas of the Hospital for 10 min each with
an airflow rate of 100 L/min (total of 1 m3), 200 L/min
(total of 2 m3) and 300 L/min (total of 3 m3), respectively.
Air samples with the Coriolis® μ were collected on wet
medium, with 4 mL of sterile phosphate buffered saline
(PBS) added to the collection cones before sampling.
total 2/44
ICU 2/8
COVID-19 ward
0/17 areas
non covid 0/19
Not attempted.
Günther T
2020
Meat Processing
Plant
GermanyStaff tested based on self‐reported
symptoms, possible contacts to
other infected persons, returning to
work after more than 96 h absence
from work
Eight air conditioning units placed near the ceiling in
the proximal half of the room constantly cool the air.
Fans project the air in a lateral direction, either directly
from frontal openings in the unit or via perforated hoses
mounted underneath the ceiling
Not attempted.Not attempted.
Guo ZD 2020HospitalChinaAir (and surface) samples of ICU and
Covid-19 wards.
Indoor air and the air outlets were sampled to detect
aerosol exposure. Air samples were collected by using
a SASS 2300 Wetted Wall Cyclone Sampler at 300 L/min
for 30 min. Samples were tested for the open reading
frame 1ab and nucleoprotein (N) genes of SARS-CoV-2 by
qRT- PCR
AIr samples:
14/40 ICU*
2/16 General
Ward
Air outlet swab
samples:
8/12 for ICUs
1/12 for GWs.
Not attempted.
Hamner L
2020 and
Miller SL 2020
Choir PracticeUSAFollow up of choir practice
attendees
In total, 78 members attended the 3rd March 2020
practice, and 61 attended the 10th March 2020 practice.
Overall, 51 (65.4%) of the 3rd March practice attendees
became ill; all but one of these persons also attended the
10th March practice. Among 60 attendees at the 10th
March practice (excluding the patient who became ill 7th
March, who also attended), 52 (86.7%) choir members
subsequently became ill. 32 were confirmed and 20
probable secondary COVID-19 cases occurred.
Not attempted.Not attempted.
Hamza H
2021
Hospital USA Air samples (< 6ft) and far-field
( >6ft) of each patient for 3.5 hours
were collected.
Air samples on filter media 17/104Not attempted.
Hemati et al.,
2021
Hospital Iran Air samples (45 SARS-CoV-2, 62
bacteria, and fungi) were collected
from different wards
The air samples for virus detection in each ward were
collected using the standard midget impinger (SKC. Inc.,
England) containing 20-mL viral transport medium (VTM)
at flow rate of 2 L min−1 for 4 h (480 L) (Faridi et al., 2020).
6/45
ICU 1/6
patient rooms
2/14
CT scan 1/2
PPE rooms 1/4
Not attempted.
Hernández JL
2020
HospitalMexicoAir samples of Emergency areas and
Covid-19 patients rooms.
Air sampled in three areas: Emergency area (Clinic
A), Internal medicine (Clinic A), COVID 19 patient area
(Clinic A), and COVID-19 patients care room (Clinic B).
Sampling in all areas was accomplished in 3 h. Filters
of 25 mm diameter with 0.22 μm pores were utilized
(Millipore, AAWP02500), placed in a sterilized filter holder
(Millipore, SWINNX) coupled to a vacuum system through
a previously disinfected plastic hose, filtering the air with a
flow of 9.6 L/min in each filter holder.
3/9 in clinic area
A and B
Not attempted.
Hoffman JS
2022
public buses USA Surveillance sampling in public
buses by installing fabric sensors in
vehicle air filtration systems.
15 actively deployed buses in the Seattle King County
Metro fleet. Collected supplementary pre-filters after
more than 7 days of being installed inside the HVAC
systems of actively-used metro buses (blue). Also
swabbed commonly-touched surfaces on the bus (red).
filters 5/37Not attempted.
Horve PF 2020
published as
Horve PF 2021
HospitalUSAAir handling units (AHUs) sampled,
including the pre-filters, final filters,
and supply air dampers.
Samples were collected using Puritan PurFlock Ultra
swabs and swabs were taken in triplicate at each AHU
location from the left, middle, and right side of each area
along the path of airflow. Swabs were pre-moistened
using viral transport media. Swabbing occurred for 20
seconds on an area approximately 20 X 30 cm at each
location and swabs were immediately placed into 15
mL conical tubes (Cole-Parmer, catalog #UX-06336-89)
containing 1.5 mL viral transport media and stored on
ice for transport to a BSL-2 laboratory with enhanced
precautions (BSL2+) lab for processing, which typically
occurred within two hours after collection.
14/56 Not attempted.
Horve PF 2021Isolation
dormitory
USACohort of subjects occupying
COVID-19 isolation dormitory and
environmental viral load over time,
symptoms, and room ventilation
Active air samples were collected using the AerosolSense
2900 sampler (Thermo Scientific, Catalog #121561-00).
The AerosolSense sampler works by drawing air into an
accelerating impactor at a rate of 200 L/min, causing
particles to impact onto a collection substrate.
Unclear Not attempted.
Hu J 2020HospitalChinaIndoor and outdoor air samples in
ICUs and CT rooms
Aerosol samples were collected over 30 min intervals
with the use of a centrifugal aerosol-to-hydrosol sampler
(WA-400, Beijing Dingblue Technology Co., Ltd., China).
Twenty-three masks from patients and 24 swabs from
surfaces in ICUs were also collected and analysed. Ten
3M™ Versaflo™ TR-600 respirator filters and 40 masks
from healthy workers in the P3 lab of Wuhan Institute of
Virology were collected for viral RNA detection. The airflow
rate of the respiratory filters was 190 L/min and the
surface area was ~30 cm2. All viral RNA positive aerosol
samples were subjected to cell culture. All viral RNA
positive aerosol samples were subjected to cell culture to
determine whether viable virus could be recovered from
them.
Aerosol samples
8/38 from ICUs
1/6 from CT
rooms
samples from
medical staff
rest areas and
corridors, were
all negative
(denominator
not clear)
All positive aerosol
samples were
negative after
three passages
of Vero-E6 cells
inoculated in a
blind test.
Jiang Y 2020HospitalChinaIndoor air samples from Covid-19
isolation ward
Air was collected by two methods: natural sedimentation
and a microbial air sampler (MAS-100 ECO), for which the
stream of air was set to exactly 100 litres/minute (Merck,
Germany).
1/28 air
samples
Not attempted.
Jin T 2020HospitalChinaAir and surface samples of ICU of
one Covid-19 patient.
Two hours after routine cleaning, high-volume air samples
were taken 0.5m from the patient bed and in the staff
PPE dressing room, using a WA 400 Portable viral aerosol
sampler at 400 L/min for 15 min at 1.5m height, while the
patient was present and was not wearing a mask.
Air sample:
0/1 staff PPE
dressing room
1/1 ICU patient
isolation room
Not attempted.
Kang M 2020Block of flatsChinaAir (and surface) sampling, and
experimental air flow study.
Air samples from 11 of the 83 flats in the building, public
areas, and building drainage systems.Investigated gas
flows and dispersion as an indicator of the movement
of virus-laden droplets in the drainage system, tracer
gas (ethane) was released into bathrooms. The hydraulic
interactions of toilet wastewater and the stack were
observed.
0/11 air
samples
Not attempted.
Kayalar O
2021
Urban Turkey Ambient particulate matter (PM)
samples in various size ranges were
collected from 13 sites including
urban and urban background
locations and hospital gardens in
10 cities
A total of 155 samples (TSP, n=80; PM2.5, n=33; PM2.5-
10, n=23; PM10, n=19) were collected daily using various
PM samplers in each city. Samples were collected on
glass fibre filters (GF) and Teflon filters (TF) with different
sampling equipment
Samplers: SKC filter sampler; dichotomous PM sampler;
high volume air sampler; low volume stack filter; Zambelli
PM sampler; High volume cascade sampler
20/203 positive Not attempted.
Kenarkoohi A
2020
HospitalIranAir sampling through hospital wards
indoor air by confirmed COVID-19
patients on 7th May 2020.
A liquid impinger biosampler calibrated for a flow rate of
12 L.min−1 at 1.5 m above ground floor and at least 2 m
away from the patient beds was used to take fourteen
air samples in different wards of the indoor air of the
hospital: ICU, ICU entrance hall, hospital entrance hall,
laboratory ward, CT scan, radiology, men internal ward,
woman internal ward and emergency ward.
Not attempted.
Kim UJ 2020HospitalKoreaSurface and air sampling.The rooms of 8 COVID-19 patients in four hospitals. On
days 0, 3, 5, and 7 of hospitalization, the surfaces in the
rooms and anterooms were swabbed, and air samples
were collected 2 m from the patient and from the
anterooms.
0/52 air
samples
positive for
SARS-CoV-2
RNA
Not attempted.
Kotwa et al.,
2021
Hospital CanadaAir and surfaces samples in rooms
of COVID-19 patients
4 bioaerosol samplers were used for sampling the first
45 patients enrolled that were not intubated. For each
patient, 1 to 2 different bioaerosol samplers were used
in each run. Using an air sampling pump (GilAir Plus
Personal Air Sampling Pump, Sensidyne, St. Petersburg,
FA), air samples were obtained using the 1-μm pore size,
37-mm polytetrafluoroethylene (PTFE) membrane filters
(SKC Inc., Eighty Four, PA), the 37-mm 3-piece cassette
with 0.8-μm polycarbonate (PC) filter (Zefon International,
Ocala, FL), and 25-mm gelatin membrane filters (SKC Inc.)
3/1460/3
Kwon KS 2020CommunityKoreaInvestigation was implemented
based on personal interviews and
data collection on closed-circuit
television images, and cell phone
location data.
A total of 39 environmental samples of inlets and outlets
of air conditioners, table seat of case A, and nearby
tables and chairs in consideration of air flow direction
were collected on June 23 for testing of SARS-CoV-2 in
the environment and were analysed by rRT-PCR test. Air
speed and direction at several specified positions were
precisely measured using a portable anemometer
0/39 positive Not attempted.
Lane MA 2020Hopsital USAAir samples in an airborne infection
isolation room, bathroom, and
anteroom of a ventilated patient
with COVID-19
Ten NIOSH BC 251 2-stage cyclone samplers were
used.9 The NIOSH samplers separated particles into 3
size fractions, which are collected in a 15 mL centrifuge
tube (>4 µm fraction), a 1.5 mL centrifuge tube (1–4 µm
fraction) and on a filter cassette containing a 37-mm
diameter, polytetrafluoroethylene filter with 2 µm pores
(<1 µm fraction).
0/28N/A
Lane MA 2021Hospital USA Air samples in nursing stations and
patient room hallways
Eight National Institute for Occupational Safety and
Health BC 251 2-stage cyclone samplers were set up
throughout 6 units, including nursing stations and visitor
corridors in intensive care units and general medical
units, for 6 h each sampling period. The NIOSH samplers
separate particles into 3 size fractions, which are collected
in a 15 mL centrifuge tube (<4 µm), a 1.5 mL centrifuge
tube (1–4 µm), and on a filter cassette containing a 37-
mm diameter, polytetrafluoroethylene filter with 2 µm
pore size (<1 µm).
total 0/528
ICU 0/384
medical unit
0/144
Not attempted.
Lednicky JA
2020a
HospitalUSAAir samples collected, and virus
culture attempted
VIVAS air samples from the room of two COVID-19
patients were set up 2m to 4.8m away from the patients.
Three serial 3-hr air samples were collected. For
each sampler, the second of the three samplings was
performed with a high efficiency particulate arrestance
(HEP A) filter affixed to the inlet tube, a process to reveal
whether virus detected in consecutive samplings reflect
true collection and not detection of residual virus within
the collector.
4/4 air samples
without a HEPA
filter
0/2 samples
using a HEPA
filter
Virus-induced CPE
were observed for
4/4 RNA-positive
air samples.
Lednicky JA
2020b
Student
Healthcare
centre
USAAir samples collected, and virus
culture attempted
The air sampling device was placed in a hallway along
which potential Covid-19 cases walked, wearing a mask,
to reach clinical evaluation rooms. The air inlet was
approximately 1.5m above floor level.
1–2General virus-
induced cytopathic
effects were
observed within
two days post-
inoculation
Lednicky JA
2021
CarUSAscreen for SARS-CoV-2 in a car
driven by a COVID-19 patient.
The Sioutas Personal Cascade impactor sampler (PCIS)
separates airborne particles in a cascading fashion and
simultaneously collects the size-fractionated particles by
impaction on polytetrafluoroethylene (PTFE) filters). It has
collection filters on four impaction stages (A–D), and an
optional after-filter can be added onto a 5th stage (E). The
PCIS separates and collects airborne particulate matter
above the cut-point of five size ranges: >2.5 μm (Stage A),
1.0–2.5 μm (Stage B), 0.50–1.0 μm (Stage C), 0.25–0.50 μm
(Stage D), and <0.25 μm (collected on an after-filter)
(Figure 1).
4/5
filter e -
equivalent
1/4
Cq 29.65
Lei H 2020HospitalChinaAir and surface samples from
the intensive care unit (ICU) and
an isolation ward for COVID-19
patients.
Air samples were collected with a two‐stage cyclonic
bioaerosol sampler (NIOSH) and an aerosol particle liquid
concentrator, between 8am and 12 noon. The NIOSH
sampler was placed on a tripod at the head of the bed
within 1m of the patient's head at a height of 1.3 m. In
the isolation ward, the sampler was also used in the
bathroom by mounting it on an infusion support near the
sink, < 1m from the toilet.
Surface and air:
1/218 ICU
samples
2/182 isolation
ward samples
Not attempted.
Li H 2021Fitness Centres USAAir and surface samples collected at
a fitness centre
Air was collected by four devices (Fig. S1): Viable Virus
Aerosol Sampler (VIVAS) and BioSpot-VIVAS (Aerosol
Devices Inc., Fort Collins, CO) as stationary samplers, and
a 47 mm PTFE filter in an in-line holder (Millipore, Bedford,
MA) and a NIOSH two-stage cyclone bioaerosol sampler
(BC-251) as personal samplers. A 3-h air sampling at 8 L
min–1 was performed during each visit using either the
VIVAS or BioSpot-VIVAS with their air intakes positioned
~1.5 m above ground in the centre of the large fitness
space on the first floor.
0/21Not attempted.
Li X 2022Employee
building
ChinaCOVID-19 outbreak with two
fast food employees infected,
using environmental SARS-CoV-2
sampling, epidemiological tracing,
viral RNA sequence as well as
surveillance method.
at the time of the outbreak there were about 20 people)
from four different companies (A–D) (Fig. 1(A)) residing
in the same employee residence building share the
same public toilet, washroom and bath rooms reserved
for female and male, respectively. The air samples were
collected into 3 mL virus culture liquid (MT0301) (Yocon
Biology Inc., Beijing, China) using one cyclone impinger
developed by Peking University and commercialized by a
company in Beijing (Fig. S2) as reported Li et al., 2021
3/20
female
washrooms n=2
0/3
Li YH & Fan YZ
2020
HospitalChinaAerosol samples & surface samples
collected in a hospital for severe
COVID-19 patients
Aerosol samples collected by an impingement air
sampler BIO-Capturer-6. 135 135 aerosol samples from
45 locations taken from the ICU ward, general isolation
wards, fever clinic, storage room for medical waste,
conference rooms and the public area.
0/135 Not attempted.
Li Y & Qian H
2020
RestaurantChina Observational and experimental:
Data from a video record and a
patron seating-arrangement from
the restaurant in Hong Kong were
collected. Secondly, the dispersion
of a warm tracer gas was assessed,
as a surrogate for exhaled droplets
No sampling performedNot attempted.N/A
Lin G 2020Block of flatsChina Case series: Nine COVID-19 cases in
one community in Guangzhou who
lived in three vertically aligned units
of one building sharing the same
piping system.
Given that all the cases occurred in the same unit and
that these households shared a common pipe system, we
therefore conducted a tracer-gas experiment to simulate
the process of potential transmission through air
Not attempted.N/A
Linde KJ 2022Nursing homesHollandAir samples in rooms of infected
patients.
In every patient room, 6-hr inhalable dust samples
were taken using a filtration-based technique at all
three locations (Conical Inhalable dust Sampler (CIS), JS
Holdings, UK). In addition, one 6-hr two-stage cyclone-
based sample with filter back-up was positioned near the
feet of the patient when bedridden or at 1.5 meters from
the chair of the patient (NIOSH BC 251,), as well as a 1-hr
impingement-based sampler positioned in proximity of
the head of the patient (5ml BioSampler, SKC, UK) The
filtration-based sampler was equipped with a 37mm
diameter 2.0μm pore-size Teflon filter. The two-stage
cyclone-based sampler allowed size-selective sampling
and was equipped with two conical tubes (of 15 ml and
1.5 ml) which sample respectively particulates of 1–4μm
and >4μm, and a back-up Teflon filter (37 mm diameter
2.0 μm pore-size Pall incorporated, Ann Arbor, USA) for
particulates of <1μm when operated at a flow of 3.5L/min.
Total: 94/213
Positive
Oraphangeal
Swab 93/184
Negative OPS
1/29
1/10
impingement-
based samples
n=4,
cyclone based n=6
CDC-NIOSH
sampler (>4µm
size fraction) had
lowest Ct of all
environmental
samples (29.5) and
was from the room
of the patient with
the lowest OPS Ct-
value (19.82).
Linillos-
Pradillo 2021
Outdoors Spainoutdoor air samples (on PM10,
PM2.5 and PM1).
Three MCV high volume (30 m3 h−1 flow) samplers
were collocated with different inlets (Digital DHA-80) for
sampling the PM10, PM2.5 and PM1 specific size fractions.
Real time particle monitors TEOM 1405DF (™Tapered
Element Oscillating Microbalance) and GRIMM™ 1107,
validated against the gravimetric reference method,
recorded PM10 and PM2.5 and PM1 mass concentration,
respectively.
0/18Not attempted.
Liu Y & Ning Z
2020
Hospital and
public spaces
ChinaMeasured SARS-CoV-2 RNA in air
samples from 2 Covid-19 hospitals,
and quantified the copy counts
using a droplet digital PCR-based
detection method
Over a 2 week period: 30 aerosol samples of total
suspended particles collected on 25-mm-diameter filters
loaded into styrene filter cassettes (SKC) by sampling air
at a fixed flow rate of 5.0 l min−1 using a portable pump
(APEX2, Casella). Three size-segregated aerosol samples
collected using a miniature cascade impactor (Sioutas
Impactor, SKC) that separated aerosols into five ranges
(>2.5 μm, 1.0 to 2.5 μm, 0.50 to 1.0 μm and 0.25 to 0.50
μm on 25-mm filter substrates, and 0 to 0.25 μm on
37-mm filters) at a flow rate of 9.0 l min−1. Two aerosol
deposition samples collected using 80-mm-diameter
filters packed into a holder with an effective deposition
area of 43.0 cm2; filters were placed intact on the floor in
two corners of an ICU for 7 days.
ICU, 2/3 positive
15/22 Isolation
wards &
ventilated
rooms
4/11 public
areas
Not attempted.
Liu W 2021HospitalChina Surface and air samples in the ICU
and general wards of three hospitals
An automatic bioaerosol sampler (WB-15, DINGBLUE
TECH, Beijing) based on the combination of cyclone
separation and impact was adopted to continuously
collect air samples for 40 min at a flow rate of 14 L min−1.
Five air samples were collected at about 30 cm from the
mouth of one corresponding patient who did not wear a
surgical mask in the ICU
1/40

ICU 1/9
General Ward
0/5
other 0/16
Not attempted.
López (a) 2021HospitalMexico Air sampling in patient rooms A vacuum pump was used to sample the air in three areas
of Clinic A and the COVID-19 patients care room of Clinic
B. Sampling in all areas was accomplished in 3 h. Filters
of 25 mm diameter with 0.22 μm pores were utilized
(Millipore, AAWP02500), placed in a sterilized filter holder
(Millipore, SWINNX) coupled to a vacuum system through
a previously disinfected plastic hose (Figure 1), filtering
the air with a flow of 9.6 L/min in each filter holder.
3-10Not attempted.
Lotta-Maria
AH 2021
Hospital & Home FinlandAir and surface samples from the
surroundings of 23 hospitalized
and eight home-treated COVID-19
patients
Seven different air collection methods were used.
A Dekati PM10 cascade impactor (20 l/min air flow) with
three stages (>10, >2.5, and >1 µm),
The impaction stages of PM10, PM2.5, and PM1 were
fitted with 25-mm-diameter cellulose acetate membrane
filters (CA filter, GE Healthcare Life Sciences) and the
backup plate with a 40-mm C
The BioSpot 300p bioaerosol sampler prototype (Aerosol
Devices Inc.)
To increase the sample collection rate, the biosampler is
equipped with eight wicking tubes fitted with three nozzle
jets to secure gentle transfer of the sample.
As a more portable solution for personal area air
sampling, a standard 25-mm gelatin (Sartorius Stedim
Biotech) or mixed cellulose ester (MCE) filter equipped in
the Button sampler with a Gilian 5000 air sampling pump,
4 l/min air flow, and a porous curved surface inlet was
used
Three Andersen cascade impactors (400 W pump and
28.3 l/min flow rate) were used simultaneously
a Dekati eFilter was used in two collections. The eFilter
monitors changes in real-time particle concentration by
utilizing a small diffusion charger powered by an inner
chargeable battery.
33/259 samples
(12/29 air
collections)
0/33
Lu J 2020RestaurantChina Study of an outbreak apparently
centred on a restaurant; air flow
studied & surface samples taken
Air samples not taken. 6 smear samples taken from the
air conditioner (3 from the air outlet and 3 from the air
inlet)
Not attempted.N/A
Luo K 2020Bus trip ChinaCase study of a SARS-CoV-2
outbreak event during bus trips of
an index patient in Hunan Province,
China.
No sampling performedNot attempted.N/A
Ma J 2020Hospital and
quarantine hotel
ChinaExhaled breath condensate (EBC)
samples were collected from 20
imported COVID-19 cases, 29 local
cases and 15 healthy controls.
EBC samples were collected using a BioScreen device
developed by Peking University. 242 surface swabs from
quarantine hotels and hospitals or from personal items of
COVID-19 patients were obtained using wet cotton swabs
14/52 EBC
sample positive;
1/26 air
samples
positive
Not attempted.
Mahdi SMS
2021
Hospital Iran Air and surfaces of ICU ward in
one of the designated hospitals in
Tehran
The air sampling was done at a distance of 1.5
to 2 meters from the patient's bed.
44840Not attempted.
Mallach G
2021
Hospital & Long
term care home
CanadaParticulate air sampling in rooms
with COVID-19 positive patients
in hospital ward and ICU rooms,
rooms in long-term care homes
experiencing outbreaks, and a
correctional facility experiencing an
outbreak.
Aerosol (small liquid particles suspended in air) samples
were collected onto gelatin filters by Ultrasonic Personal
Air Samplers (UPAS) fitted with <2.5μm (micrometer) and
<10 μm size-selective inlets operated for 16 hours (total
1.92m3), and with a Coriolis Biosampler over 10 minutes
(total 1.5m3).
ICU 4/23
Ward 7/92
LTC 3/15
Correctional
facility 1/8
0/15
Marchetti R
2020
HospitalItalyAir sampling in three different
hospitals in Milan, Italy.
For particles’ sampling the AEROTRAK™ Portable Airborne
Particle Counter was used for cleanroom particles
classification. For microbiological air sampling, the SAS
Super IAQ Surface Air System (model 90593), which
conveys a known volume of air during a fixed period on
Petri Plates filled with Standard Plate Count Agar (PCA)
was used. Ten AIRcel units per hospital were placed in
three different hospitals in Milan, Italy. In total 68 samples
were processed in three distinct test sessions between
April and June 2020, using the QIAGEN Rotor-Gene
thermal cycler.
E gene 19/68
samples,
ORF1ab + N
detected in 7/68
samples.
.
Not attempted.
Masoumbeigi
H 2020
Military hospitalIranRandom air sampling with
continuously sterilised sample
equipment
All patients aged 55–65 were either intubated or had
severe symptoms. Sampling of 100–1000 l for 20 mins
in two randomly chosen stations 0.5 metres from the
beds. RT-PCR performed at 42 cycles. Air sampling was
done (n = 31) on selected wards including Emergency 1,
Emergency 2, bedridden (4-B, 10-D), ICU 2, ICU 3, CT-
SCAN, and laundry.
0/31Not attempted.
McGain F
2020
HospitalAustraliaCase report of a tracheostomy
procedure; air samples were
collected throughout
Two spectrometers to measure aerosol particles: the
portable Mini Wide Range Aerosol Sizer 1371 (MiniWRAS)
and the Aerodynamic Particle Sizer (APS). During the
procedure, the aerosol detector inlet was positioned 30
cm directly above the patient’s neck, representing the
surgeon’s breathing air space
Not attempted.Not attempted.
Moharir SC
2022
Hospital &
homes
India Air, samples from different locations
occupied by coronavirus disease
(COVID-19) patients
Air samples were collected on disposable gelatin filters
(Sartorius, Cat. No. 17528-80-ACD) using AirPort MD8
air sampler (Sartorius, Cat. No. 16757). 1000 L of air was
collected at a flow rate of 50 L per minute and a sampling
time of 20 min.
hospital 40/80
ICU 10/22
non ICU 20/58
pts home 10/18
1/3 in the home
setting
Moreno T
2020
Buses and
Subway Trains
Spain75 samples from buses and 24
from subway trains, collected from
surfaces using swabs (78 samples),
from ambient air (12 samples),
and from air-conditioning filters (9
samples)
Air sampling in the subway took place June 17–19, 2020
on three consecutive days. Six samples of particulate
matter with a diameter of <2.5 µm (PM2.5) were
collected inside 6 trains using 47 mm Teflon filters with
PEM (Personal Environmental Monitor) equipment. The
sampling of the buses took place between 20:00 and
03:00 on the night of May 25–26, 2020 in one of the four
main bus depots in Barcelona. After sampling, the bus
was disinfected.
1/6 air samples
on buses gave
weak positive
result
2/6 subway
trains
Not attempted.
Morioka S
2020
HospitalJapan2 case reports Air was sampled using an MD8 airscan sampling device
and sterile gelatin filters. Air was sampled twice at a speed
of 50 L/minute for 20 minutes in the negative-pressure
rooms of two patients and its associated bathrooms.
0/2 patient 1
0/2 patient 2
Not attempted.
Mouchtouri
2020
Hospital, nursing
home, LTCF & a
ferry
Greece Air and Surface samples from
a ferryboat during a COVID-19
ongoing outbreak investigation and
a nursing home and from three
COVID-19 isolation hospital wards
and a long-term care facility
portable air sampler (Sartorius Airport MD8) with air flow
set to 50 L per minute and 10 min sampling time. Gelatin
membrane filters of 80 mm diameter (Sartorius 17528-80-
ACD) were used.
1/12 air
samples
Not attempted.
Mponponsuo
K 2020
HospitalCanadaEpidemiological study investigating
airborne versus droplet
transmission of SARS-CoV-2
Air samples not taken. From 5 HCWs with positive
SARS-CoV-2 tests and Covid-19 symptoms, no onward
transmission was observed from 72 exposures
Not attempted.Not attempted.
Nagle S 2022HospitalFranceair and surface contamination in the
rooms of patients with COVID-19 in
the acute phase of the disease.
Air sampling of 600 litres in 6 minutes at 1 and 3 meters,7/59 Not attempted.
Nakamura K
2020
HospitalJapanNasopharyngeal, environmental and
air samples from patients
11 air samples in three negative pressure bays (Bay 1
to Bay 3), a single negative pressure room in a general
ward (Room 1) and a single negative pressure room
in an isolation ward (Room 2) using an MD8 airscan
sampling device (Sartorius, Goettingen, Germany) and
sterile gelatin filters (80 mm diameter and 3 μm pores
; Sartorius). We placed the device on the floor about 1.5
meters–2 meters away from the patient's head. Air was
sampled twice, at a speed of 50 L/minute for 20 minutes,
in the negative pressure rooms and its associated
restrooms
0/11 Not attempted.
Nannu
Shankar S
2021
Apartments USAAir and surfaces in bedrooms
of two 20-year-old persons with
symptomatic COVID-19 were
sampled self-isolating persons.
Using polytetrafluoroethylene (PTFE) filters and a Viable
Virus Aerosol Sampler (VIVAS), (2) size-fractionated
particles in aerosols according to aerodynamic size using
a 2-stage cyclone aerosol sampler (NIOSH bioaerosol
sampler, BC-251) and a Sioutas personal cascade
impactor sampler (PCIS), The PCIS (catalog no. 225–370,
SKC Inc., US) was used with a Leland Legacy pump
(catalog no. 100–3002, SKC Inc., US) and operated at a
flow rate of 9 L/min for 90 min. PTFE filters (25 mm, 0.5
μm pore, catalog no. 225–2708, SKC Inc., US) were used
to collect particles of size >2.5 μm, 1–2.5 μm, 0.5–1 μm
and 0.25–0.5 μm in the 4 collection stages.
Volunteer A
NIOSH 1/3
PTFE 0/3
Volunteer B
NIOSH 4/6
PCIS 4/10
volunteer B
Oct 2 4/8*
Oct 6 0/8
Nor 2021Hospitals Malaysia Fine indoor air particulates with a
diameter of ≤ 2.5 µm (PM2.5) was
collected over four weeks during
48-h measurement intervals in four
separate hospital wards
Air purifier (FANFIL AP510M, Aire-plus Technology,
Singapore) was deployed at ~ 1 m distance in wards C and
D, ~ 8 m in ward B, and no air purifier in single occupant
room.
2–4Not attempted.
Nissen K 2020HospitalSwedenObservational: surface swabs
and fluid samples collected, and
experimental: virus culture was
attempted.
In a Covid-19 ward, surface samples were taken at air vent
openings in isolation rooms and in filters. Fluid sample
collections were done in the ventilation system. Separate
HEPA filter systems, distance measured to between
49 and 56 meters. Admitted patients in the ward were
between day 5 and 23 after symptom onset
7/19 room
vents
11 days later,
4/19 for both
genes.
8/9 main
exhaust filters
+ve for both
genes.
No significant CPE
was seen after
three passages on
Vero E6 cells from
samples retrieved
from ward vent
openings or central
ventilation ducts or
filters
Ogawa Y 2020 HospitalJapanObservational study of 15 HCP
who had contact exposures (15/15)
and aerosol exposures (7/15) to a
hospitalized Covid-19 patient who
re-tested positive 18 days after
initial negative PCR.
Air sampling not performed, All PCR tests performed on
exposed HCWs using a nasopharyngeal swab obtained
on the 10th day after the exposure were negative, and
the results of the tests for IgG antibodies to SARS-CoV-2
on the specimens collected approximately 20 days after
exposure were also negative.
Not attempted.N/A
Ong SWX
2020
HospitalSingaporeAir, surface and PPE swab samples
collected for 3 hospitalized Covid-19
patients.
Air sampling was done on 2 days using SKC Universal
pumps (with 37-mm filter cassettes and 0.3-μm
polytetrafluoroethylene filters for 4 hours at 5 L/min)
in the room and anteroom and a Sartorius MD8
microbiological sampler (with gelatin membrane filter for
15 minutes at 6 m3/h) outside the room. Supplemental
file Blue icons labelled A to E indicate the position of the
air samplers within the room (A to C), anteroom (D), and
common corridor (E).
0/5 Not attempted.
Ong SWX
2021
Hospital &
Community
Air samples from airborne-infection
isolation rooms and a community
isolation facility housing COVID-19
patients
Air samples were collected using a BioSpot-VIVAS BSS300-
P bioaerosol sampler (Aerosol Devices, Fort Collins, CO),
which collects airborne particles using a water-vapor
condensation method into a liquid collection medium at a
flow rate of 8 L per minute.
6–120/6
Orenes-Piñero
E 2020
HospitalSpanish Study of COVID-19 traps to measure
the capacity of SARS-CoV-2 aerosol
transmission.
“COVID-19 traps "were placed only in the rooms
of patients with a confirmed positive diagnostic.
Interestingly, the rooms where COVID-19 patients were
isolated had a ventilation rate of 1800 m3/h. 6 different
surfaces trapped in boxes with plastic, protective grids
to avoid that samples could be touched by the patient
or by the healthcare personnel. The different surfaces
were: polypropylene (PP), glass, polyvinyl chloride (PVC),
methacrylate, agar medium and carbon steel. PP surfaces
were obtained from PP black panels and had a semi-gloss
finish with a thickness of 2 mm.
0/18 ICU "traps"
2/18 Covid
wards "traps"
Not attempted.
Pan J 2022Student rooms USAcollected surface swab samples
and heating, ventilation, and air
conditioning (HVAC) filters from 24
rooms that had been occupied by
students who tested positive for
COVID-19,
collected HVAC filters from each room, if
available, cut them into ∼3 cm × 8 cm pieces, and stored
them
at −80 °C. swabbed the air exhaust grilles in the public
bathrooms in the quarantine dormitory.
15/21 HVAC
4/6 bathroom
exhaust grilles
Culture samples
with a Ct value
< 33, and none
contained
culturable virus.
Passos RG
2021
Hospital and
community
Belo
Horizonte
BRAZIL
Environmental and hospital air
sampling from May to August 2020
62 samples from two hospitals with different occupancy
and public plazas, bus stations/terminals, and hospital
areas, with a large circulation and concentration of
people. "The epidemiological situation during this
monitoring period suggested an accelerated spread of
the virus in the city"
5/62 (ICU 3/22)
ward areas 2/20
Not attempted.
Pivato A 2021EnvironmentalPadua,
Veneto, Italy
Remote sampling of PM from
outdoor environmental stations
10 outdoor sites were sampled from 23 Feb to 8 March
2020 before national lockdown. A total of 44 PM 2.5 and 5
samples were taken
0/44Not attempted.
Pochtovyi AA
2021
HospitalRussiaPilot study of the presence
of SARS-CoV-2 in aerosol samples
and surface swabs from different
locations in the respiratory
infection department and ICUs
of the First Infectious Diseases
Hospital in Moscow
.
Air and surface samples collected from rooms of PCR and
clinically diagnosed C19 patients in the two departments.
Graphics in the paper show sampling sites and results.
Samples taken from floors, corridors, handles, beds,
nurses stations, cafeteria etc of patients

5/15 (5/6 ICU
samples, 0/9
other areas)
Not attempted.
Ramuta MD
2022
Community
setting in
Wisconsin and
Minnesota
USAObservational study assessing
whether active air samplers can be
used for prospective air surveillance
of SARS-CoV-2 in real-world
congregate settings between July
19, 2021, to February 9, 2022
527 air samples from 15 different locations such as coffee
shops and sports facilities. In total, nine samples with
RdRp Ct-values ranging from 19.8 to 30.2 were selected
for SARS-CoV-2 whole-genome sequencing, of which
six OPS, one cyclone-based sample, one filtration-based
sample and one surface swab.
106/527
52 inconclusive.
Not attempted.
Razzini K 2020HospitalItalyObservational; 5 air (& 37 surface)
samples collected in the ICU for
Covid-19 patients.
Air samples done using an MD8 Airport Portable Air
Sampler with gelatine membrane filters, 1 filter for each
monitored area.
Each aspiration cycle was 40 min with a flow of 50 l/min.
The detector was positioned 1.5 m above the floor. Air (n
= 5) samples were collected from three zones classified
as contaminated (corridor for patients and ICU), semi-
contaminated (undressing room) and clean areas: (lockers
and passage for the medical staff and a dressing room).
20/20 from the
contaminated
area
0/8 semi-
contaminated
0/9 clean areas.
Not attempted.
Ruffina de
Sousa 2022
Hospital Sweden sample air from rooms occupied
by COVID-19 patients in a major
hospital.
Room air was collected using the Tuberculosis Hotspot
detector (THOR) electrostatic air sampler. Ten different
patient rooms with adjoining anterooms were sampled in
the above way.
patient rooms
9/22; adjoining
anterooms
10/22
PFU recovery
patient room 3/9;
anteroom 8/10
Santarpia JL
2020a
HospitalUSASize-fractionated aerosol samples
collected; virus culture was
attempted.
Air samplers were placed in various places in the vicinity
of the patient, including over 2m distant. Personal air
sampling devices were worn by study personnel on two
days during sampling. Measurements were made to
characterize the size distribution of aerosol particles,
and size-fractionated, aerosol samples were collected to
assess the presence of infectious virus in particles sizes of
>4.1 µm, 1–4 µm, and <1 µm in the patient environment.
An Aerodynamic Particle Sizer Spectrometer was used to
measure aerosol concentrations and size distributions
from 0.542 µm up to 20 µm. A NIOSH BC251 sampler was
used to provide size segregated aerosol samples for both
rRT-PCR and culture analysis.
6/6 patient
rooms.
In 3 aerosol
samples of
size <1 μm, cell
culture resulted
in increased viral
RNA.
Viral replication
of aerosol was
also observed
in the 1 to 4 μm
size but did not
reach statistical
significance.
Santarpia JL
2020b
Healthcare
centre
USAHigh-volume (50 Lpm) and low-
volume (4 Lpm) personal air
samples (& surface samples)
collected from 13 Covid-19 patients;
virus culture was attempted.
We initiated an ongoing study of environmental
contamination obtaining surface and air samples in 2
NBU hospital and 9 NQU residential isolation rooms
housing individuals testing positive for SARS-CoV-2.
Samples were obtained in the NQU on days 5–9 of
occupancy and in the NBU on day 10. Samples collected
using a collected using a Sartorius Airport MD8 air
sampler operating at 50 Lpm for 15 min.
63% of in-room
air samples
positive
(denominator
unclear)
Cultivation of
virus was not
confirmed in these
experiments.
Schoen CN
2022
Medical centre/
maternity wing
USACase series of 6 term mothers who
tested positive up to 7 days before
SVD. 5/6 wore masks throughout
labour and delivery. Study took
place between May 2020 and
January 2021.
Two samplers were used: 1 at the bedside, midway
between the subject’s head and hips at about 4 feet high
and
2 was located 6–10 feet from the subject’s head, ∼5 feet
high.
0/12Not attempted.
Semelka CT
2021
Academic
hospital
North
Carolina US
To assess effect of mask on viral
spread two 30 minute sampling
runs were undertaken. One with
COVID patients without a mask
followed by a run with the patient
wearing a mask.
59 adults with Covid 19 and comorbidities aged around
58 yrs. provided 20 samples each: 9 samples
from both environmental sampling runs (3 stations with 1
surface sample and 2 pooled samples from air sampling
devices), the patient mask, and the initial NP swab.
2/52. Not attempted.
Setti L 2020Outdoor
sampling
ItalyObservational study of particulate
matter collected in industrial area of
Bergamo over a continuous 3-week
period
Particulate matter was collected using fibre filters by using
a low-volume gravimetric air sampler (38.3 l/min for 24
h), compliant with the reference method EN12341:2014
for PM10 monitoring. This sampling procedure allows
collection of aerosol and bioaerosol, by filtering 55 m3 per
day, in a wide dimensional range; an approach considered
suitable for sentinel and surveillance purposes.
20/34 PM
samples
positive for one
gene
4/34 positive for
2 genes
Not attempted.
Seyyed Mahdi
SM 2020
Hospital Iran Cross-sectional study in the Covid-
19 ICU ward.
Air and surface sampling; impinger method was applied
for air sampling: at a distance of 1.5 to 1.8 meters from
the ground, the air of the ICU ward was passed through
a sampling pump with an flow rate of 1.5 l/min into the
porous midget impeller-30 ml containing 15 ml of virus
transmission medium (PVTM) for 45 minutes.
6/10 air
samples
Not attempted.
Shen Y 2020Community
including
transport on
buses
ChinaObservational epidemiology: cohort
of 128 individuals.
128 individuals travelled on 1 of 2 buses to attend a
worship event in Eastern China. Those who rode a bus
with air recirculation and with a patient with COVID-19
had an increased risk of SARS-CoV-2 infection compared
with those who rode a different bus.
Not attempted.Not attempted.
Stern RA 2021
(a)
Mid sized
hospital in
Boston
USASimultaneous air sampling in five
sites six times in the period 29 April
to 22 May 2020. N gene PCR probe
Cascade samplers were located at floor height:
(1) outside the entrance to a COVID-19 ward (CW1); (2)
in a personal protective equipment (PPE) donning room
outside the entrance to another COVID-19 ward (CW2);
(3) outside the entrance to the medical intensive care
unit (ICU); (4) at a staff workstation in the emergency
department (ED); and (5) at a nursing staff workstation
of a ward not designated for care of COVID-19 patients
(NCW)
8/90
6 difference
time points,
5 different
sampling areas
ICU: 2/18
ED: 2/18
Covid Ward:
1/36
Non CW: 3/18
Not attempted.
Stern RA 2021
(b)
30 locations
in a hospital
and a COVID-
19 quarantine
facility.
Kuwait210 air samples collected
simultaneously over two periods:
April 30 - May 20, 2020 and
June 24 - July 10, 2020
Samples from ICUs, nurses' workstations, the rooms of
inpatients with and without symptoms, observation rooms
for the ED, locker rooms, bathrooms, a lobby, waiting
areas, patient hallways, swab testing areas, and outside
hospital entrances.
13/210 Not attempted.
Song Z 2020Public Health
Clinical Centre
China Observational surveillance
to evaluate the risk of viral
transmission in AIIRs with 115
rooms in three buildings at the
Shanghai Public Health Clinical
Centre, Shanghai, during the
treatment of 334 patients infected
with SARS-CoV-2.
In patient rooms, an air sampler was placed on the
ground with a distance of about 1.0 m from patient’s
bed. In changing rooms, it was located between air
supply outlet and air exhaust to capture particles from
the unidirectional airflow. In addition, HEPA filters of air
exhaust outlet in AIIRs in building 2 were collected.
0/7 ICU air
samples
0/2 non ICU
buildings

.
Not attempted.
Tan L 2020HospitalChina Observational study of air and
surface samples collected from
isolation wards and ICU for 15
COVID-19 patients.
Air samples were obtained by placing an air sampler
within 1 m of the patient’s head; this continuously filtered
air at a speed of 5 l/min and trapped small virus particles
on a membrane. After 1 h the membrane was removed
and cut into small pieces to be stored in VTM prior to
further testing. The air sampler was placed at the same
height as (or slightly lower than) an electronic fan installed
on top of the windows to expel the air from the wards
to the outside. Air samples were obtained from patient
rooms, the corridor outside the patient rooms, and in
the nearby nursing stations. Samples were collected with
a cascade sampler running continuously for 48 hours
collecting fine (≤2.5 μm aerodynamic diameter),
coarse (2.5–10 μm) and large (≥10 μm) particles
1/29
0/17 clean areas
1/12 patient
rooms*
Not attempted.
Thuresson S
2022
HospitalSwedenObservational study carried out
Skåne, southern Sweden from
March 20 to April 21 to assess
variables associated with SARS-CoV-
2 in the air: patient characteristics,
distance from patient, room
ventilation, and supportive
treatment with a focus on potential
AGPs.
Air samples were taken for 10 minutes, several times a
week, in 3 infectious disease wards, 4 ICUs, 3 medical
wards modified into COVID-19 units, and 1 ED. Patient
records were examined: PCR and Ct were recorded.
26/310;
22/231 within
patient rooms
Not attempted.
Vosoughi M
2021
HospitalIran Samples of air were taken from
respiratory section-1 (COVID-19),
laboratory section, CT section,
respiratory section-2 (COVID-19),
respiratory section-1 (COVID-
19) check-up room, respiratory
section-2 (COVID-19) station section,
emergency section, and ICU.
Samples were taken 2 to 5 m from
beds and at different heights (1 to 2
mt). Map provided in paper.
32 samples taken from areas with 55 SARS-CoV-2 positive
patients and 35 HCWs
0/32Not attempted.
Wei L 2020 (a) HospitalChina Sampled the surroundings and air
of 6 negative-pressure non-ICU
rooms
In a designated isolation ward occupied by 13 Covid-19
patients, including 2 asymptomatic patients. Air was
sampled between 10:30 am and 13:00 pm during the
routine medical activities using an air sampler (FSC-1V;
Hongrui, Suzhou, China) with 0.22-μm-pore-size filter
membranes for 15 min at 100 litres/min. The air sampler
was placed about 0.6 m away from each patient and 1 m
above the floor in each room. The filter membranes were
wiped by the use of pre moistened sterile swabs (Copan).
0/6 room air
samples
Not attempted.
Wei L (2020
(b)
HospitalChina Observational study in patient
surroundings and on PPE in a non-
ICU isolation ward
The air from rooms for nine COVID-19 patients with
illness or positive PCR > 30 days, before and after
nasopharyngeal/oropharyngeal swabbing and before and
after nebulization treatment. Air sampling was performed
using an air microbiological sampler (FSC-1V; Hongrui,
Suzhou, China) with 0.22 μm filter membranes on a
nutrient agar plate for 15 min at 100 L/min, which was
placed about 2 m away from patient and 1.1 m above the
ground. Air was also sampled before and after performing
nebulization treatment for all patients required (n = 4 on
March 4 and n = 2 on March 12, 2020). After air sampling,
the filters and the surface of agar were wiped using sterile
swabs.
0/34 room air
samples
Not attempted.
Winslow R
2021
HospitalUKProspective observational study
of 30 low SATS Covid-19 cases
who received either supplemental
oxygen, CPAP or HFNO (10 in each
arm). The study took place between
11/12/2020 and 19/02/2021
NP swab, plus 3 air and 3 surface samples taken from
each ppt and the clinical environment. Air samples were
taken with a Coriolis micro air sampler. Recruitment was
opportunistic. PCR was carried out with ORF1a and N
genes probes.
4/90 1/51
nasopharyngeal
sample
Wong JCC
2020
Home residenceSingapore Observational study of
environmental contamination of
SARS-CoV-2 in non 24 healthcare
settings and assessed the efficacy
of cleaning and disinfection
in removing SARS-CoV-2
contamination.
Air samples were collected (n=4) in an accommodation
room (occupied by Case 1) that was thought to be poorly
ventilated and another 2 samples were collected right
outside the room entrance. All samples were taken after
the infected persons vacated the sites and have been
isolated in healthcare facilities.
0/6 home
residence
samples
Not attempted.
Wong SCY
2020
HospitalChina Case report and contact tracing
and testing outbreak investigation
of a patient in with COVID-19 who
was nursed prior to Covid diagnosis
in an open cubicle of a general
hospital ward, Hong Kong.
Samples not collected.Not attempted.Not attempted.
Wu S 2020HospitalChina Observational study of air and
surface samples in hospital
including rest rooms
Air samples from medical areas were collected through
natural precipitation according to the Hygienic Standard
for Disinfection in Hospitals.9 All samples were collected
under emergency conditions around 8:00 AM before
routine cleaning and disinfection
0/44
0/13 ICU
0/13 Wards
0/18 fever clinic
N/A
Yarahmadi R
2021
ICUIran Sampling stations were located
around various parts of ICU as
described in Figure 1
20 air samples taken around ICU from 3 zones: patient
breathing
zone, general area, breathing zone of health
care personnel.
4/20
2/4 patient
breathing zone
1/8 general
area;
1/8 HCW
breathing zone
Not attempted.
Yuan XN 2020HospitalChina Observational study of the
contaminated area in COVID-19
wards
Air samples from the clean area, the buffer room and
the contaminated area in the COVID-19 wards using a
portable bioaerosol concentrator WA-15.
0/90 Not attempted.
Zhang D 2020Outdoor
environment of 3
hospitals
China Air (and wastewater and soil
samples) collected from the
surroundings of a Covid-19 hospital.
73 air and wastewater samples from the environment of
three hospitals in Wuhan treating Covid-19 patients.
3/16 Not attempted.
Zhang X 2022Non clinical areas
of University
buildings
University
of Michigan,
US
Observational study to assess air
and surface contamination, relating
it to the epidemiological situation
and estimating the risk of infection
with SARS-CoV-2
Between August 2020 and April 2021 areas in classrooms,
rehearsal rooms, office areas, cafeterias, buses, gyms,
student activity buildings and heating, ventilation and
air-conditioning (HVAC) system tunnels were wet swabbed
(surfaces) or air sampled. Results were linked to University
dashboard for linkage with case incidence
4/256 (1,6%) air
samples and
4/517 (1.5%)
surface samples
Not attempted.
Zhou J 2020HospitalUKObservational: (air & surface)
samples collected from a hospital
with a high number of Covid-19
inpatients.
In the Emergency Department dedicated for patients with
confirmed or suspected COVID-19, two of the cubicles
were occupied and one patient was in the ambulatory
wait area at the time of sampling. These areas were
disinfected daily using a combined chlorine-based
detergent/disinfectant (Actichlor Plus, Ecolab), with an
additional twice daily disinfection of high touch surfaces
using the same detergent/disinfectant. In each of these
clinical areas, four air samples were collected (five air
samples were collected in the Emergency Department,
and three in public areas of the hospital). Air sampling
was performed using a Coriolis μ air sampler (referred
to as Coriolis hereafter) (Bertin Technologies), which
collects air at 100–300 litres per minute (LPM). After 10
min sampling at 100 LPM, a total of 1.0 m3 147 air was
sampled into a conical vial containing 5 mL Dulbecco’s
minimal essential medium (DMEM).
2/31 air
samples
positive
12/31
suspected
0/14
Zhou L 2020HospitalChina Study of collected samples of
exhaled breath of patients ready for
discharge and air samples.
The 13 patients in 4 hospitals were aged 70+ years. 10
were recovered Covid-19 patients ready for discharge;
3 were patients recovered from influenza who tested
negative for SARS-CoV-2). Air (& surface) samples were
collected. Exhaled breath condensate of 300–500 L
was collected from each patient: a long straw was used
to allow the patient to breathe into a tube that was
electrically cooled.
44 air samples were taken, from corridors, hospital waste
storage rooms, ICU rooms (5 samples), toilets, medical
preparation rooms, clinical observation rooms, and
general wards. Two impinger samplers were used: WA-15
sampled at a flow rate of 15 L/min, while the WA-400
sampled at 400 L/min.
0/44 Not attempted.

Table 2. Study characteristics: reviews.

Study Id
(n=29)
Fulfils
systematic
review
methods
Research question
(search date up to)
No. included studiesMain resultsKey conclusions
Airborne
transmission
(n=22)
Anderson EL
2020
noWhat are the scientific uncertainties
and potential importance of aerosol
transmission of SARS‐CoV‐2. (search
methods and date not clear)
unclear Limited evidence reports that SARS-CoV-2 can
remain active in aerosol for at least 3 hours,
although its concentration decreases over time.
Further data collection required
assessment under differing conditions
of temperature and humidity. Such
research should be relatively low cost
and results available in a short time.
Aghalari Z
2021
yesTo evaluate the SARS-COV-2
transmission through indoor air
in hospitals and its prevention
practices (search December 2019
to October 1, 2020).
11 studies incuded in
qualitative synthesis
Analysis of the articles showed that Asian
countries (Iran, China, Singapore) were more
concerned with the SARS-COV-2 transmission
through hospital air. Four articles did not
confirm SARS-COV-2 in the air, but seven
articles reported the SARS-COV-2 from air
samples.
Several factors can affect the positive
or negative SARS-COV-2 detection in
air samples, such as environmental
conditions in hospitals, sampling
methods, sampling height and distance
from patients, flow rate and sampling
time, efficiency and functionality of
ventilation systems, use of disinfectants.
Agarwal 2020yesTo summarize the evidence for
the efficacy, safety, and risk of
aerosol generation and infection
transmission during high-flow nasal
cannula (HFNC) use among patients
with acute hypoxemic respiratory
failure due to COVID-19 (search
conducted to 14 May 2020)
4 studies evaluating
droplet dispersion
and three evaluating
aerosol generation
and dispersion.
Two simulation studies and a crossover study
showed mixed findings regarding the effect of
HFNC on droplet dispersion. Two simulation
studies reported no associated increase in
aerosol dispersion, and one reported higher
flow rates were associated with increased
regions of aerosol density (evidence rated as
very low certainty).
High-flow nasal cannula may reduce
the need for invasive ventilation and
escalation of therapy
Bahl P 2020noWe aimed to review the evidence
supporting the rule of 1-meter (≈3
feet) spatial separation for droplet
precautions in the context of
guidelines issued by the WHO, CDC,
and European Centre for Disease
Prevention and Control (ECDC) for
HCWs on respiratory protection for
COVID-19. (open search to March
2020)
10 papers We found that the evidence base for current
guidelines is sparse, and the available data do
not support the 1- to 2-meter (≈3–6 feet) rule of
spatial separation. Of 10 studies on horizontal
droplet distance, 8 showed droplets travel
more than 2 meters (≈6 feet), in some cases
up to 8 meters (≈26 feet). Several studies of
severe acute respiratory syndrome coronavirus
2 (SARS-CoV-2) support aerosol transmission,
and 1 study documented virus at a distance of
4 meters (≈13 feet) from the patient.
The weight of combined evidence
supports airborne precautions for the
occupational health and safety of health
workers treating patients with COVID-19.
Birgand G
2020 and
Birgand G
2020JAMA
noEvidence for airborne contamination
of SARS-CoV-2 in hospitals (search
conducted to 21 Jul y repeated
on October 27, 2020 for JAMA
publication)
17 articles 68/247 (28%) of air sampled from close
patients environment were positive for
SARS-CoV-2: no difference according to the
setting (ICU: 27/97, 27.8%; non-ICU: 41/150,
27.3%; p=0.93), or the distance from patients
(<1 metre: 1/64, 1.5%; 1 to 5 metres: 4/67, 6%;
p=0.4). 3/78 (4%) viral cultures performed in
three studies were positive (all were samples
from close to patients). JAMA: A total of 81 viral
cultures were performed across 5 studies, and
7 (8.6%) from 2 studies were positive, all from
close patient environments.
In hospital, the air near and away
from COVID-19 patients is frequently
contaminated with SARS CoV-2 RNA, with
however, rare proofs of their viability.
JAMA in this systematic review, the air
close to and distant from patients with
coronavirus disease 2019 was frequently
contaminated with SARS-CoV-2 RNA;
however, few of these samples contained
viable viruses. High viral loads found in
toilets and bathrooms, staff areas, and
public hallways suggest that these areas
should be carefully considered.
Carducci A
2020
noTo describe the state of the art of
coronavirus airborne transmission
(search conducted 5 June)
64 papers classified
into three groups:
laboratory
experiments
(12 papers), air
monitoring (22) and
epidemiological and
airflow model studies
(30
Airborne transmission of SARS-CoV-2 was
suggested by studies across the three groups,
but methods were not standardised.
No studies had sufficient confirmatory
evidence, and there is only a hypothesis
to support airborne transmission
Chen PZ 2020yesTo develop a comprehensive dataset
of respiratory viral loads (rVLs)
of SARS-CoV-2, SARS-CoV-1 and
influenza A(H1N1)pdm09 (search
conducted to 7 Aug)
64 studies (n = 9,631
total specimens)
Modelling of the likelihood of respiratory
particles containing viable SARS-CoV-2.
When expelled by the mean COVID-19 case
during the infectious period, respiratory
particles showed low likelihoods of carrying
viable SARS-CoV-2. Aerosols (equilibrium
aerodynamic diameter [da] ≤ 100 µm) were
≤0.69% (95% CI: 0.43-0.95%) likely to contain
a virion. Droplets also had low likelihoods: at a
equilibrium aerodynamic diameter = 330 µm,
Aerosols (≤100 μm) can be inhaled
nasally, whereas droplets (>100 μm) tend
to be excluded. For direct transmission,
droplets must be sprayed ballistically
onto susceptible tissue. Hence,
droplets predominantly deposit on
nearby surfaces, potentiating indirect
transmission. Aerosols can be further
categorized based on typical travel
characteristics: short-range aerosols
(50-100 μm) tend to settle within 2 m;
long range ones (10-50 μm) often travel
beyond 2 m based on emission force;
and buoyant aerosols (≤10 μm) remain
suspended and travel based on airflow
profiles for minutes to many hours
Cherrie JW
2021
No To summarise the reported
SARS-CoV-2 RNA air and surface
contamination concentrations in
workplace settings where the virus is
present, particularly considering the
quality of the methods used, to draw
lessons for future methodological
developments (up to the 24th
December 2020)
35 papers were
reviewed: three were
available as preprints
and the remainder
as peer-reviewed
publications
Typically, around 6% of air and surface samples
in hospitals were positive for SARSCOV-2 RNA,
although there is very limited data for non-
healthcare settings.
• The quality of the available measurement
studies is generally poor, with little
consistency in the sampling and analytical
methods used.
• Few studies report the concentration of
SARS-CoV-2 in air or as surface loading of
virus RNA, and very few studies have reported
culture of the virus.
• The best estimate of typical air concentrations
in health care settings is around 0.01
SARS-CoV-2 virus RNA copies/m3
The reliability of the reported data
is uncertain. The methods used for
measuring SARSCoV-2 and other
respiratory viruses in work environments
should be standardised to facilitate
more consistent interpretation of
contamination and to help reliably
estimate worker exposure.
Comber L
2020
yesTo synthesise the evidence for the
potential airborne transmission of
SARS‐CoV‐2 via aerosols. (Searches
1 Jan up to 27 July 2020).
28 studies (8
epidemiological case
series of SARS-CoV-2
clusters or outbreaks;
16 air sampling
studies, and 4
virological studies).
10/16 air sampling studies detected
SARS‐CoV‐2 ribonucleic acid; however, only
three of these studies attempted to culture
the virus with one being successful in a limited
number of samples. Two of four virological
studies using artificially generated aerosols
indicated that SARS‐CoV‐2 is viable in aerosols.
The results of this review indicate there
is inconclusive evidence regarding the
viability and infectivity of SARS‐CoV‐2
in aerosols. Epidemiological studies
suggest possible transmission, with
contextual factors noted. However,
there is uncertainty as to the nature
and impact of aerosol transmission of
SARS‐CoV‐2, and its relative contribution
to the Covid‐19 pandemic compared with
other modes of transmission.
Dinoi A 2021 Identification/quantification of
SARS-CoV-2 RNA in airborne samples
comparing different sites: outdoor
sites, indoors in hospitals and
healthcare settings, and community
indoor locations. (Start of COVID-19
pandemic until 31/08/2021)
73 published papers
on experimental
determination of
SARS-CoV-2 RNA in air
11.7% of studies are in outdoor, 75.3% in
hospitals, and 13% in community public
indoors.
•Average positivity rate was larger in
hospital compared to outdoors and public indoor sites.
•Contamination of surfaces was more frequent
than air but with a lower positivity rate.
•SARS-CoV-2 RNA concentrations in air follows
outdoors<public indoors<hospitals.
Concentrations of SARS-CoV-2 RNA in air
were highly variables and, on average,
lower in outdoors compared to indoors.
Among indoors, concentrations in
community indoors appear to be lower
than those in hospitals and healthcare
settings.
Ekram W 2020no To summarize the ways in which
SARS-CoV-2 is transmitted (Searches
Dec 28, 2019 up to July 31 2020)
unclear Evidence-based hypotheses support the
possibility of SARS-CoV-2 airborne transmission
due to its persistence in aerosol droplets in a
viable and infectious forms.
Aerosolized transmission is likely the
dominant route for the spread of SARS-
CoV-2, particularly in healthcare facilities.
Although SARS-CoV-2 has been detected
in non-respiratory specimens, including
stool, blood and breast milk, their role in
transmission remains uncertain.
Ji B 2020no To reviews the information from
published papers, newsletters
and large number of scientific
websites to profile the transmission
characteristics of the coronaviruses
in water, sludge, and air
environment, (search methods and
date not clear)
unclear It appears that the wastewater, sludge,
aerosol are potentially environmental
transmission of coronavirus.
Mehraeen E
2020
noTo review the current evidence of
COVID-19 transmission modes.
(Searches Dec 2019 to April 2020)
36 studies including
31 articles (11 reports,
eight reviews, seven
letters to the editor,
two modeling, one
perspective, and two
experimental studies)
and five clinical trials.
Identified five potential transmission modes of
COVID-19 including airborne, droplet, contact
with contaminated surfaces, oral and fecal
secretions.
Droplet and contact with contaminated
surfaces were the most frequent
transmission modes of COVID-19. Fecal
excretion, environmental contamination,
and fluid pollution might contribute to a
viral transmission
Niazi S 2020noTo evaluate the mechanisms of
generation of human pathogenic
coronaviruses, evaluating these
viruses in the air/field studies and
available evidence about their
seasonality patterns. (searches no
restriction on year up to July 31
2020)
total unclear (8
Studies of air
sampling: 6
Sars-CoV-2)
Evidence exists for respirable-sized airborne
droplet nuclei containing viral RNA, although
this does not necessarily imply that the virus
is transmittable, capable of replicating in a
recipient host, or that inoculum is sufficient to
initiate infection. However, evidence suggests
that coronaviruses can survive in simulated
droplet nuclei for a significant time (>24 h).
Nevertheless, laboratory nebulized virus-
laden aerosols might not accurately model
the complexity of human carrier aerosols in
studying airborne viral transport
Human respiratory activities generate
respirable sized aerosols that are of
adequate size to support an infectious
virus. Knowledge of the properties of
respiratory aerosols and their effects
on the viability of viruses remains
incomplete. Environmental factors
could directly affect the viability of virus
on the embedded viruses in aerosols.
There is disagreement on whether wild
coronaviruses can be transmitted via
an airborne path. Further studies are
required to provide supporting evidence
for the role of airborne transmission.
Noorimotlagh
Z 2020
noTo review studies on airborne
transmission of SARS-CoV-2 in indoor
air environments.(search methods
and date not clear)
14 studies 11 studies were experimental and reported
different findings on positive or negative
detection of SARS-CoV-2 airborne transmission
in indoor air. Among them, three studies
indicated that all indoor air samples in the
hospital were negative, thus concluding
that there is no evidence that SARS-CoV-2
is transmitted by air (Faridi et al., 2020; Kim
et al., 2020; Masoumbeigi et al., 2020). the
other included experimental studies reported
positive results that confirmed transmission of
the virus through the air.
There is a possibility of airborne
transmission of SARS-CoV-2 in indoor air
environments.
Rahmani 2020noA review of methods used for
sampling and detection of SARS like
viruses in the air. (search methods
and date not clear)
not clear Factors that limit the interpretation included
variable patient distance from the sampler,
use of protective or oxygen masks by patients,
patient activities, coughing and sneezing
during sampling time, air movement,
air conditioning, sampler type, sampling
conditions, storage and transferring conditions.
Most studies are not able to discriminate
between airborne or respiratory droplet
transmission.
Ren SY 2020NoThis review aims to summarize
data on the persistence of different
coronaviruses on inanimate surfaces.
(search date unclear)
unclear Viruses in respiratory or fecal specimens can
maintain infectivity for quite a long time at
room temperature. Absorbent materials like
cotton are safer than unabsorbent materials
for protection from virus infection. The risk of
transmission via touching contaminated paper
is low. Preventive strategies such as washing
hands and wearing masks are critical to the
control of coronavirus disease 2019.
Viruses in respiratory or fecal specimens
can maintain infectivity for quite a long
time at room temperature. Absorbent
materials like cotton are safer than
unabsorbent materials for protection
from virus infection. The risk of
transmission via touching contaminated
paper is low.
Palmer JC
2021 & Duval
D 2022
yes To evaluate the potential for long
distance airborne transmission of
SARS-CoV-2 in indoor community
settings and to investigate factors
that might influence transmission.
(search 1 Jan 2020 to 19 Jan 2022)
22 reports relating to
18 studies
Long distance airborne transmission was likely
to have occurred for some or all transmission
events in 16 studies and was unclear in two
studies (GRADE: very low certainty). In the
16 studies, one or more factors plausibly
increased the ikelihood of long distance
airborne transmission, particularly insufficient
air replacement (very low certainty), directional
air flow (very low certainty), and activities
associated with increased emission of
aerosols, such as singing or speaking loudly
(very low certainty). In 13 studies, the primary
cases were reported as being asymptomatic,
presymptomatic, or around symptom onset at
the time of transmission.
Authors suggest long distance airborne
transmission of SARS-CoV-2 might occur
in indoor settings such as restaurants,
workplaces, and venues for choirs, and
identified factors such as insufficient air
replacement that probably contributed
to transmission
Ribaric NL
2021
Yes Assessed the nature and extent of
air- and surface-borne SARS-CoV-2
contamination in hospitals to identify
hazards of viral dispersal and enable
more precise targeting of infection
prevention and control. (Until June
2021)
51 observational
cross-sectional
studies comprising
6258 samples were
included.
SARS-CoV-2 RNA was detected in one in six
air and surface samples throughout the
hospital and up to 7.62 m away from the
nearest patients. The highest detection rates
and viral concentrations were reported from
patient areas. The most frequently and heavily
contaminated types of surfaces comprised air
outlets and hospital floors. Viable virus was
recovered from the air and fomites.
The nature and extent of hospital
contamination indicate that SARS-CoV-2
is likely dispersed conjointly through
several transmission routes, including
short- and long-range aerosol, droplet,
and fomite transmission.
Singhal S 2020noTo focus on different modes
of transmission of this virus,
comparison of this virus with
previous similar analogy viral
diseases like SARS and MERS
(Searches Jan 1 to 29 April 2020)
unclear Analysis of different papers on mode of
transmission it was found that this virus is
highly contagious and spreads through air
droplet, close contact, through fomites and
different metallic surfaces and through aerosol
in surroundings with high aerosol generating
procedures only.
Results demonstrate the fact that early
screening, social distancing, isolation
of symptomatic patients, respiratory
etiquette are the main armaments
presently to deal with this virus till
effective treatment or vaccine becomes
available in the near future.
Vardoulakis S
2021
NoReview of the environmental
sampling, laboratory, and
epidemiological studies on viral and
bacterial infection transmission in
washrooms (Search dates
2000-2020)
38 studies from 13
countries
A wide range of enteric, skin and soil bacteria
and enteric and respiratory viruses were
identified in public washrooms, potentially
posing a risk of infection transmission.
Although there is a risk of microbial
aerosolisation from toilet flushing
and the use of hand drying systems,
we found no evidence of airborne
transmission of enteric or respiratory
pathogens, including COVID-19, in public
washrooms.
Wilson NM
2020
noTo assess the airborne transmission
of severe acute respiratory syndrome
coronavirus‐2 to healthcare workers
(search methods and date not clear)
unclear Evidence largely from low-quality case and
cohort studies where the exact mode of
transmission is unknown as aerosol production
was never quantified. The mechanisms and
risk factors for transmission were also largely
unconfirmed.
Limited evidence suggests aerosol
generating procedures cause an
increase in airborne healthcare worker
transmission. Further research is
required.
Airborne transmission and procedures (n=4)
Goldstein KM
2021
YesRisk of viral transmission during
nebulizer treatment of patients with
coronavirus disease 2019 (search
updated to to Sep 1 2020)
22 articles: 1
systematic review, 7
cohort/case-control
studies, 7 case series,
and 7 simulation-
based studies. Eight
individual studies
involved patients with
SARS, five involved
MERS, and one
involved SARS-CoV-2.
one stduy found with COVID19 patients -
Heinzerling et al.
Specific evidence that exposure
to nebulizer treatment increases
transmission of coronaviruses similar to
COVID-19 is inconclusive.
Hussain A
2020
noExtent of infectious SARS-CoV-
2 aerosolisation as a result of
oesophagogastroduodenoscopy or
colonoscopy (search conducted up
to 5 June)
26 studies The aerosolisation and infectious extent of
SARS-CoV-2 cannot be accurately measured,
and no clinical studies have confirmed aerosol
infection of SARS-CoV-2,
Kay JK 2020yesWhat is the evidence for minimizing
the use of flexible laryngoscopy
during the coronavirus disease 2019
pandemic? (search conducted upto
April 2020)
No studies provided
data for SARS-CoV-2
transmission during
flexible laryngoscopy.
A paucity of data regarding the risks of
SARs-CoV-2 aerosolization and transmission
during endoscopic procedures of the
aerodigestive tract
More research is needed.
Schünemann
HJ
yesTo review multiple streams of
evidence regarding the benefits and
harms of ventilation techniques for
coronavirus infections, including
that causing COVID-19 (search
conducted up to 1 May).
45 studies COVID-19)Evidence suggests an increased risk for
transmission of coronaviruses with invasive
procedures. An additional 34 studies in
COVID-19 patients were found, by their
methods and reporting were too poor to
synthesize data appropriately.
Direct studies in COVID-19 are limited
and poorly reported.
Ventilation, air conditioning filtration and recirculation (n=3)
Mousavi EH
2020
noWhat is the safety of air filtration
and air recirculation in healthcare
premises. (search methods and
date not clear)
109 documents
categorized into five
levels
Evidence to support current practice is very
scarce. No randomized trials were retrieved
and most experiments were designed to try to
prove airborne transmission as opposed to test
the null hypothesis. Observational evidence
and animal studies showed contaminated
air can result in disease spread, and the
combination of air filtration and recirculation
can reduce this risk.
There is a need for a rigorous and
feasible line of research in the area of air
filtration and recirculation in healthcare
facilities.
Chirico F 2020noWhat is the impact of heating,
ventilation and air conditioning
systems (HVAC) on transmission of
coronaviruses (search conducted
11 July)
6 studies on
SARS-CoV-2
In three of six studies of SARS-CoV-2, the
heating and ventilation system was suspected
to aid transmission; in two studies the data did
not support such an effect, and in one study
only modelling suggested an impact
The differences in HVAC systems prevent
generalization of the results. The few
investigations available do not provide
sufficient evidence that SARS-CoV-2 can
be transmitted by HVAC systems.
Correia G
2020
noWhat is the impact of HVAC in
hospitals or healthcare facilities on
the spread of the virus. (search
methods and date not clear)
unclear The authors speculate that incorrect
use of HVACs might contribute to the
transmission of the virus.

Reviews

We found 29 reviews on SARS-CoV-2: 22 reviews [Anderson EL 2020, Agarwal 2020, Aghalari 2021, Bahl P 2020, Birgand G 2020, Carducci A 2020, Chen PZ 2020, Cherrie JW 2021, Comber L 2020, Dinoi A 2021, Ekram W 2020, Ji B 2020, Mehraeen E 2020, Niazi S 2020, Noorimotlagh Z 2020, Palmer JC 2021, Rahmani 2020, Ribaric NL 2021, Ren Y 2020, Singhal S 2020, and Wilson NM 2020, Vardoulakis S 2021] were about airborne transmission and prevention; four reviews were about airborne transmission and procedures [Goldstein KM 2021, Hussain A 2020, Kay JK 2020, and Schünemann HJ] and three were about ventilation, air conditioning filtration and recirculation [Mousavi EH 2020, Chirico F 2020, and Correia G 2020] (see Table 2). The final search date of these reviews ranged from April 2020 up to January 2022. Only nine reviews met systematic review methods criteria that include systematically searching for all available evidence, appraising the quality of the included studies, and synthesising the evidence into a usable form13.

Quality of included primary studies (n=128)

All included primary studies were observational (some with experimental components) and of low quality (see Table 3). We could not identify a published protocol for any of the studies. Most studies were based on convenience sampling. While the description of methods provided sufficient detail to replicate them in 87% of studies (see Figure 2), the research often lacked standard methods, standard sampling sizes and standard reporting. In 57% of the studies, the sample sources were clear, however, outcomes that aimed to demonstrate the detection of culturable, replicable viruses were lacking. The variation in sample methods coupled with flaws in the reporting made it difficult to distinguish between aerosol and droplet nuclei transmission routes. Interpretation was further limited by the variability in reporting of patient distance from the sampler, use of protective equipment or oxygen masks by patients, time since symptom onset, patient activities (coughing and sneezing during sampling time), air movement, air conditioning sampler design, method of sampling, storage, and transfer conditions.

Table 3. Quality of included studies.

StudyIs the
source popn
adequately
described
Description
of methods
and sufficient
detail to
replicate
Samples
sources
clear and
quantified
Analysis &
reporting
outcomes
appropriate
Was follow up
sufficient
Adenaiye OO 2021YesYesYesNoNot Applicable
Alkalamouni H 2021UnclearUnclearYesYesNot Applicable
Ahn JY 2020YesYesNoUnclearNot Applicable
Ang AX 2021UnclearYesYesNoNot Applicable
Baboli 2021UnclearYesYesNoNot Applicable
Baribieri P 2021 UnclearYesYesYesNot Applicable
Barksdale AN 2020UnclearUnclearYesNoNot Applicable
Bays D 2020YesYesNot ApplicableYesYes
Bazzazpour S 2021UnclearYesYesYesNot Applicable
Ben-Shmuel 2020UnclearYesYesYesNot Applicable
Binder 2020YesYesYesYesYes
Bokharaei-Salim F
2021.
UnclearYesUnclearYesNot Applicable
Cai Y 2020UnclearUnclearYesYesNot Applicable
Charlotte N 2020YesUnclearNot ApplicableUnclearYes
Cheng VCC 2020aYesYesYesYesNot Applicable
Cheng VCC 2020bUnclearYesYesUnclearNot Applicable
Cheng VCC 2021YesYesYesNoNot Applicable
Chia PY 2020YesYesYesYesNot Applicable
Chirizzi D 2020Not ApplicableYesYesYesNot Applicable
Coleman KK 2021YesYesYesNoNot Applicable
Conte M 2021YesYesYesYesNot Applicable
Declementi M 2020YesYesYesYesNot Applicable
De Man P 2020UnclearYesNot ApplicableUnclearNot Applicable
Di Carlo P 2020Not ApplicableYesYesYesNot Applicable
de Rooij MMT 2021YesYesYesYesNot Applicable
Ding Z 2020YesYesYesUnclearNot Applicable
Döhla M 2020UnclearYesYesUnclearNot Applicable
Dubey A 2021YesYesYesUnclearNot Applicable
Dumont-Leblond 2020YesYesYesYesNot Applicable
Dumont-Leblond N
2021
UnclearYesYesUnclearNot Applicable
Dziedzinska R 2021YesYesYesYesNot Applicable
Escudero D 2021YesUnclearYesUnclearNot Applicable
Faridi S 2020YesYesYesYesNot Applicable
Feng B 2021YesYesYesYesNot Applicable
Ge 2020UnclearYesYesYesNot Applicable
Ghaffari HR 2021UnclearYesYesNoNot Applicable
Gharehchahi E 2021UnclearYesYesUnclearNot Applicable
Gholipour S 2021UnclearYesYesNoNot Applicable
Gomes da Silva P 2022UnclearYesYesYesNot Applicable
Günther T 2020YesYesYesUnclearYes
Guo ZD 2020YesYesYesYesNot Applicable
Hamner & Miller 2020YesYesNot ApplicableUnclearYes
Hamza H 2021UnclearUnclearUnclearYesNot Applicable
Hemati et al., 2021YesYesYesUnclearNot Applicable
Hernández JL 2020UnclearYesYesYesNot Applicable
Hoffman JS 2022UnclearUnclearYesYesNot Applicable
Horve PF 2020 &
Horve PF 2021
UnclearUnclearYesUnclearNot Applicable
Horve PF 2021YesYesYesUnclearUnclear
Hu J 2020UnclearYesYesUnclearNot Applicable
Jiang Y 2020YesYesUnclearUnclearNot Applicable
Jin T 2020YesYesYesYesNot Applicable
Kang M 2020YesYesUnclearUnclearNot Applicable
Kayalar O 2021UnclearYesYesUnclearNot Applicable
Kenarkoohi A 2020YesYesYesUnclearNot Applicable
Kim UJ 2020YesYesYesYesNot Applicable
Kotwa et al., 2021YesYesYesYesNot Applicable
Kwon KS 2020YesYesNot ApplicableYesYes
Lane MA 2020YesYesYesYesNot Applicable
Lane MA 2021UnclearYesYesYesNot Applicable
Lednicky JA 2020aYesYesYesUnclearNot Applicable
Lednicky JA 2020bYesYesYesUnclearNot Applicable
Lednicky JA 2021YesYesYesYesNot Applicable
Lei H 2020YesYesYesYesNot Applicable
Li H 2022UnclearYesYesUnclearNot Applicable
Li X 2022UnclearYesYesUnclearUnclear
Li YH & Fan YZ 2020YesYesYesYesNot Applicable
Li Y & Qian H 2020YesYesNot ApplicableYesYes
Lin G 2020YesYesNot ApplicableYesNot Applicable
Linde KJ 2022UnclearYesYesYesNot Applicable
Linillos-Pradillo 2021UnclearYesYesYesNot Applicable
Liu Y, Ning Z 2020YesYesYesYesNot Applicable
Liu W 2021UnclearYesUnclearYesNot Applicable
López 2021UnclearYesUnclearUnclearNot Applicable
Lotta-Maria AH 2021YesYesYesUnclearNot Applicable
Lu J 2020YesUnclearNot ApplicableUnclearNot Applicable
Luo K 2020YesYesNot ApplicableYesYes
Ma J 2020UnclearYesYesUnclearNot Applicable
Mahdi SMS 2021UnclearUnclearYesUnclearNot Applicable
Mallach G 2021UnclearYesYesYesNot Applicable
Marchetti 2020YesYesUnclearUnclearNot Applicable
Masoumbeigi 2020YesYesYesYesNot Applicable
McGain FYesYesUnclearUnclearNot Applicable
Moharir SC 2022UnclearYesYesUnclearNot Applicable
Moreno 2020Not ApplicableYesYesYesNot Applicable
Morioka S 2020YesYesYesUnclearNot Applicable
Mouchtouri 2020UnclearNoYesUnclearNot Applicable
Mponponsuo K 2020YesYesNot ApplicableYesYes
Nagle S 2022YesYesYesYesNot Applicable
Nakamura K 2020UnclearYesYesYesNot Applicable
Nannu Shankar S 2021YesYesYesYesNot Applicable
Nissen K 2020YesUnclearYesUnclearNot Applicable
Nor 2021UnclearUnclearUnclearUnclearNot Applicable
Ogawa Y 2020YesYesYesYesYes
Ong SWX 2020YesYesYesYesNot Applicable
Ong SWX 2021YesYesYesYesNot Applicable
Orenes-Piñero E 2020YesYesNot ApplicableYesNot Applicable
Pan J 2022UnclearYesYesYesNot Applicable
Passos RG 2021UnclearYesYesNot ApplicableNot Applicable
Pivato A 2021UnclearYesYesYesNot Applicable
Pochtovyi AA 2021UnclearYesYesYesNot Applicable
Ramuta MD 2022UnclearYesYesYesNot Applicable
Razzini K 2020YesYesYesYesNot Applicable
Ruffina de Sousa 2022UnclearYesYesYesNot Applicable
Santarpia JL 2020aYesYesYesUnclearNot Applicable
Santarpia JL 2020bYesYesYesNoNot Applicable
Schoen CN 2022YesYesYesUnclearNot Applicable
Semelka CT 2021YesYesYesUnclearNot Applicable
Setti L 2020Not ApplicableYesYesYesNot Applicable
Seyyed Mahdi SM 2020YesYesYesUnclearNot Applicable
Shen Y 2020UnclearYesNot ApplicableNoUnclear
Stern RA 2021 (a)UnclearYesYesUnclearNot Applicable
Stern RA 2021 (b)YesYesYesUnclearNot Applicable
Song Z 2020UnclearYesYesYesNot Applicable
Tan L 2020YesYesYesUnclearNot Applicable
Thuresson S 2022YesYesYesUnclearNot Applicable
Vosoughi M 2021UnclearYesYesYesNot Applicable
Wei L 2020aYesYesYesYesNot Applicable
Wei L 2020bYesYesYesYesNot Applicable
Winslow R 2021YesYesYesYesNot Applicable
Wong JCC 2020YesYesUnclearYesNot Applicable
Wong SCY 2020YesYesNot ApplicableYesYes
Wu S 2020YesUnclearYesUnclearNot Applicable
Yarahmadi R 2021YesYesYesNoNot Applicable
Yuan XN 2020UnclearUnclearUnclearUnclearNot Applicable
Zhang D 2020YesUnclearYesUnclearNot Applicable
Zhang X 2022UnclearYesYesNoYes
Zhou J 2020YesYesYesYesNot Applicable
Zhou L 2020YesYesYesYesNot Applicable
Total731111016712
128128128128128
Percentage57.0%86.7%78.9%52.3%9.4%
9ad1e537-1b7b-4130-8ba5-352576faa348_figure2.gif

Figure 2. Risk of Bias Airborne Transmission Studies (n=128).

Primary studies

We included 128 primary studies, of which 105 (82%) reported binary data on RT-PCR air samples (see Table 1). All the studies were observational. Twenty-eight studies (22%) reported Ct values and 36 studies (28%) reported copies per sample volume (see Table 4).

Table 4. Concentrations of PCR samples recovered.

Of the 128 included studies, 54 (42%) reported viral concentrations (see Table 3). Of these, 31 reported data on cycle threshold and 36 on genome copies. The lack of standardized reporting prevents the pooling of the data. Thirteen studies reported both cycle threshold and genome copies: de Rooij 2021, Dumont-Leblond 2020, Guo 2020, Kayalar 2021, Lednicky 2020a, Lednicky 2020b, Lednicky 2021, Ma 2020, Mallach 2021, Nannu Shankar 2021, Nor 2021 Passos 2021, and Pochtovyi 2021).

EIght studies reported air samples with a cycle threshold below 30: Ang 2021, Dubey 2021, Guo 2020, Linde 2022, Mallach 2021, Nannu Shankar 2021, Ramuta 2022, Razzini 2020. Infectivity (defined by virus growth in VERO cell culture) is highly likely when the RT-PCR Ct value is <25. [reference Jefferson et al.] We found five studies that reported CTs below this threshold: Dubey 2021, Guo 2020, Nannu Shankar 2021, Ramuta 2022, and Razzini 2020.

StudyCycle Threshold (Ct)Copies per m3 (or L)
Ang AX 2021E-gene: 29.55–37.22
N-Gene: 34.30–38.95
Baboli 20212.53 - 4.86
copies/m3
Baribieri P 202119th 20th & 21st June range 36.7–38.3
22nd, 23rd June 06/20 negative or > 40
Ben-Shmuel 2020Ventilated patient: 34.1
Nurse station: 38.8
Quarantine hotel: 35
Binder 2020Sample at 1.4m, <4uM: 1st 36.6; 2nd 37.1
Sample at 2.2m, <4uM: 1st 37.4, 2nd 39.9
Sample at 2.2m, >4uM: 1st 39.1, 2nd 39.6
Chia PY 2020Range 1.84 ×103-3.38 ×103 copies per m3
Chirizzi D 2020<0.8 copies m3 for each size range.
Cheng VCC 202133.2–38.0
Coleman KK 2021Activity N gene copies per expiratory activity
Breathing (30 mins): 63.5–550
Talking (15 mins): 79.9–4336
Singing (15 mins): 135–5821
de Rooij MMT
2021
385×102 copies/m3
Ding Z 2020RNA copies for weakly positive sample not calculated.
Dubey A 2021Ward:                1m.                   3m
E gene:         16.1–32.1       21.1–29.7
RdRp-gene:  16.1–29.4.      29.9–34.1
ICU:                  1m.                       3m
E gene:         19.1–30.2      29.9–32.5
RdRp-gene:  16.8–30.3      30.5–33.7
Emergency Ward In the centre
E gene:          26.7–30.2
RdRp-gene:  24.1–34.0
Nursing station separated by glass wall
E gene:         -ve, RdRp-gene: -ve
Dumont-Leblond
N 2020
N gene (range 36.5 to 39.8) mean 38.0
ORF1b gene (32.1 to 35.2) mean 33.7
Mean 201 genomes /m3 (range 9.9 to 514)
Feng B 2020<1 μm: 1,111 copies/m3
>4 μm: 744 copies/m3
Ge XY 202036.5 - 37.8
Gomes da Silva P
2022
ICU: 60 min sampling (flow rate 50 L/min)
N1 gene 6000 copies/m3 N2 gene 6575 copies/m3
First 10 min (flow rate 100 L/min)
N1 6362.5 copies/m3 N2 6662.5 copies/m3
Guo ZD 2020Indoor air near air outlet: 35.7
Near patients: 44.4
Near the doctor’s office: 12.5
Indoor air near the air outlet: 3.8/L
near the patients: 1.4/L
near the doctor’s office: 0.52/L
Horve PF 2020The highest abundance sample (~245 gene copies) found on the pre-filters,
Hu J 2020Range 1.11 ×103 to 1.12 ×104 copies m3
In 10% of outdoor air samples,
10 m from the doors of inpatient & outpatient buildings range 0.89 to 1.65×103
copies m3
Kayalar O 2021RdRp-gene 34.7 to >45
N gene 35.1 to >45
N gene 9917 - 43790 uL-1
80 – 504 copy numbers on the filters
Kenarkoohi A
2020
Around 38 for ORF1ab
Around 35 for n gene
Lednicky JA 2020a36.0, 37.7, 37.4, 38.7 (mean Cq 37.5)2.82E+03, 9.12E+02, 1.15E+03, 4.68E+02 genome equivalents/25 μL,
Lednicky JA 2020b39.10.87 virus genome equivalents L-1
Lednicky JA 202133.5–40.11.24E+03 - 3.14E+04
Lei H 2020Near the head of the patient Ct 41.25.
Linde KJ 2022Range from 29.5 to 37.2
Lotta-Maria AH
2021
COVID-19 ward
Active sampling
Range 534–6608 cm-3 (3380 ± 2320 cm-3),
Passive sampling 1 sample 3.56 x 103 copies/ml.
Liu Y & Ning Z
2020
ICU: range- 0 –113 copies m3
Patient areas 0 –19 copies m3
Medical Staff Areas 0 – 42m3
Public areas: 0 –11copies m3
Ma J 2020Exhaled Breath Samples, 35.5 ± 3.2Breath emission rate estimate: 1.03 × 10 to 2.25 × 10 viruses per hour.
Air sample estimate 6.1 × 10 3 viruses/m3
Mahdi SMS 2021Highest RNA concentrations were observed between beds 6 and 7: 3913 copies/ml.
Mallach G 2021N gene range 30.2– 38.0, mean 35.5 (SD 2.1)
E gene range 27.0– 36.9, mean 33.6 (SD 2.3)
Ct E gene (range)
ICU 33.0 (31.2-34.3)
Ward 35.0 (33.3-36.89)
Long term Care (LTC) 3968.3 (27.0-35.0)
Correctional Facility 32.4
Mean RNA copy numbers
E gene 941.6 copy numbers/mL (range 61.3–11,462; SE 752.4)
mean RNA concentration in the air 1202.4 copy numbers/m3 (63.8–11939.9; SE
977.2);
Copy numbers mean (range)
ICU 224.8 (71.6-529)
Ward 134.3 (61.3-276.0)
LTC 3968.3 (89.0-11462.3)
Correctional Facility 378.9
Moreno T 2020Genome count range
IP2: 14 to 446/m2 for IP2,
IP4: 9 to 490/m2
E subway 5 to 378/m2:
1st sample estimate 23.4 GC/m3,
2nd amplified target gene IP2 (18.8 GC/m3) protein E (5.6 GC/m3).
Nagle S 20221m: median 38 (range 37–40)
3m: 40 (range 39–42)
Nannu
Shankar S 2021
Patient A:
NIOSH sampler: 38.2
Patient B: Oct 2
PCIS sampling
RdRp gene: 16.0–18.0
N gene 14.6–16.8
NIOSH sampler
RdRp gene: 16.0–18.0 18.5–32.0
N gene: 17.1–31.1
Patient B: Oct 6
PCIS: RdRp gene, N gene -ve
NIOSH: RdRp gene: -ve N gene: 37.7
Patient A: GE/cm3 of air
NIOSH sampler: 0.06
Patient B: Oct 2
PCIS sampling
RdRp gene: 3.01 × 104 - 1.19 × 105
N gene: 6.84 × 104 - 3.04 × 105
NIOSH sampler
RdRp gene: 9.89 × 102 - 6.36 × 104
N gene: 2.54 × 103 - 1.68 × 105
Patient B: Oct 6
PCIS: RdRp gene, N gene: -ve
NIOSH: RdRp gene: -ve N gene: 0.16
Nissen K 2020Ct N gene: 35.3
Ct E gene 33.2
Ward 1 specimen Ct 33.0 for E gene only.
Nor 2021 < 40Ward A: 74 ± 117.1 copies μL−1
General Ward B: 10 ± 7.44 copies μL−1
Ong SWX 2021179 to 2,738 copies/m3
Orenes-Piñero E
2020
Ct from surfaces > 10 cycles of those obtained from the patient, indicating
viral load was lower in the room environment.
Pan J 2022Quarantine rooms
Average 31 copies/m3 (Range 0.3 to 115)
Isolation rooms
Average 3 copies/m3 (0.2 to 24)
Passos RG 202132–34genomic units m3
0.19 -66.4
Pochtovyi AA
2021
Close to detection limit: 38–40 28.1 to 140.6 copies per/m3
Ramuta MD 2022Emergency housing facility: 25.9–31.8
Brewery Taproom: 30.0–42.9
Razzini K 2020ICU: Mean Ct 22.6
Corridor: Mean Ct 31.1
Ruffina de Sousa
2022
Average Ct
Patient rooms: 38.3
Anterooms 38.3
Air exhaust vent in the patient room: 33.5 Air exhaust vent in the anteroom:
33.0
Santarpia JL
2020a
Concentrations up to around 7.5 TCID 50 /m3 of air.
Santarpia JL
2020b
In-room air samples mean 2.42 copies/L of air
NBU Room A (Patient 1) 2.42 copies/L
NBU Room B (Patient 3),
Near the patient: 4.07 copies/L
>2 m from the patient’s bed: 2.48 copies/L
Outside rooms in hallways: 2.51 copies/L.
Highest concentrations in NBU while a patient was receiving oxygen through a
nasal cannula (19.17 and 48.22 copies/L).
Seyyed Mahdi SM
2020
Highest RNA concentrations observed between beds 6 and 7 (3,913 copies per ml)
Stern RA 2021 (a)Range 7–51
Highest concentrations in ED, May 13–15: 51 copies/m3
2nd highest at Non-Covid Ward, May 11–13: 47 copies/m3
Stern RA 2021 (b)Outside hospital gates: 3–17 copies/m3 Symptomatic patient rooms: 8–25 copies/m3
ICUs: 18–21 copies/m3
Outdoors,
Gate 7: 17 copies/m3
Thuresson S 2022In patient rooms median concentration:
115 copies/m3 (IQR 31 to 232)
Winslow R 2021Ct values for positive and suspected-positive air samples were substantially
higher than paired samples in the nasopharynx, indicating minimal viral
RNA in the air.
Zhang D 2020Range 285 to 1,130 copies/m3.
Inside adjusting tank 285 copies/m3 and 603 copies/m3.
5 m from Hospital outpatient building 1,130 copies/m3,
5 m from the inpatient building undetected
Zhang X 2022Gym: weight room: 15/10/20 (sample time
257 mins) 6.00 × 10−2 gc/L,
Gym: weight room: 30/10/20 (253 mins): 2.80 × 10−2 gc/L
Gym: weight room 2/8/21 (242 mins): 7.60 × 10−2 gc/L
Bus: passenger area 18/11/20 (72 mins): 2.30 × 10−2 gc/L
Gym: weight room in Fall: 2.80 × 10−2 gc/L
Gym: weight room Fall & Winter: 6.00 × 10−2 gc/L
Zhou J 2020101 to 103 copies of SARS-CoV-2 RNA in all air samples; no significant difference
between sample areas.

Of the 128 included studies, 54 (42%) reported viral RNA concentrations (see Table 3). Of these, 31 reported data on Ct and 36 on genome copies. The lack of standardized reporting prevents the pooling of the data. Thirteen studies reported both Ct and genome copies [de Rooij MMT 2021, Dumont-Leblond 2020, Guo ZD 2020, Kayalar O 2021, Lednicky JA 2020a, Lednicky JA 2020b, Lednicky JA 2021, Ma J 2020, Mallach G 2021, Nannu Shankar S 2021, Nor 2021, Passos RG 2021, and Pochtovyi AA 2021]. Only eight studies reported air samples with a RT-PCR Ct below 30: Ang AX 2021, Dubey A 2021, Guo ZD 2020, Linde KJ 2022, Mallach G 2021, Nannu Shankar S 2021, Ramuta MD 2022, Razzini K 2020. We found five studies that reported Cts below this threshold: Dubey A 2021, Guo ZD 2020, Nannu Shankar S 2021, Ramuta MD 2022, and Razzini K 2020. Infectivity (defined by virus growth in Vero cell culture) has been found to be more likely when the RT-PCR Ct value is <25.14

Table 5 shows 24 studies reporting the size of detectable particles containing RNA from SARS-CoV-2 [Adenaiye OO 2021, Baboli 2021, Baribieri P 2021, Binder 2020, Chia PY 2020, Chirizzi D 2020, Coleman KK 2021, Feng B 2020, Hernández JL 2020, Kayalar O 2021, Lednicky JA 2021, Linde KJ 2022, Liu Y & Ning Z 2020, Lotta-Maria AH 2021, Mallach G 2021, McGain F 2020, Nannu Shankar S 2021, Ong SWX 2021, Passos RG 2021, Semelka CT 2021+, Santarpia 2020a, Stern RA 2021a, Stern 2021b and Zhang X 2022]. Overall, the methods used for air sampling were heterogeneous across studies. SARS-CoV-2 RNA was detectable in a range of air sample sizes from <1 μm through to >18 µm. Thirteen studies detected particles below <4 μm, and Chirizzi D 2020 et al. reported on coarse particles up to a diameter > 18 µm. Different samplers in the same study also detected different size particles. For example, McGain F 2020 et al. reported that the APS detected larger aerosols (> 0.37 µm) and MiniWRAS smaller particles (0.01–0.35 µm).

Table 5. The size of air particles in the sample.

Twenty-four studies reported detecting RT-PCR SARS-CoV-2 test positive RNA in a wide range of sizes (see Table 4).

StudySamples SourceSize of air particles
Adenaiye OO
2021
30-minute breath samples while vocalizing into a Gesundheit-II, 2 paired breath
samples 1 with and 1 without a mask; 1 or 2 visits 2 days apart.
Coarse (> 5 µm) 25/149
Fine (≤ 5 µm) 24/149
Baboli 2021Fifty-one indoor air samples were collected in two areas, with distances of less
than or equal to 1 m (patient room) and more than 3 m away (hallway and nurse
station) from patient beds.
PM1, PM2.5, and PM10 detected
Baribieri P
2021
PM10 was collected by a low noise (<35 dB) air sampler (SILENT Air Sampler—FAI
Instruments S.r.l., Roma, Italy) for 24 h on quartz fibre filters.
PM!0
Binder 2020EIght National Institute for Occupational Safety and Health (NIOSH) BC 251
Aerosol Samplers were placed 1.5m from the ground, at ~1 meter, ~1.4
meters, ~2.2 meters, and ~3.2 meters from the SARS-CoV-2 patient’s head and
subsequently run for ~4 hours. 195 air samples were collected
Aerosol particle size <4 µm
Chia PY 2020Air sampling was performed in three of the 27 airborne infection isolation rooms
(AIIRs). Bioaerosol samplers were used to collect air samples, set at a flow rate
of 3.5 L/min and run for four hours, collecting a total of 5,040 L of air from each
patient’s room.
positive particles of sizes >4 µm
and 1–4 µm detected in two
rooms
Chirizzi D 2020The genetic material of SARS-CoV-2 (RNA) was determined using both real-time
RT-PCR and ddPCR in air samples collected using PM10 samplers and cascade
impactors able to separate 12 size ranges from nanoparticles (diameter D <
0.056 µm) up to coarse particles (D > 18 µm).
(D < 0.056 µm) up to coarse
particles (D > 18 µm)
Coleman KK
2021
Used a G-II exhaled breath collector to measure viral RNA in coarse and fine
respiratory aerosols emitted by COVID-19 patients during 30 minutes of
breathing, 15 minutes of talking, and 15 minutes of singing. participants were
seated facing the truncated cone-shaped inlet, with air drawn continuously
(130 L/minute) around the subject’s head and into the sampler. Aerosols were
collected in 2 size fractions, namely coarse (>5 μm) and fine (≤ 5μm).
All three activities
Coarse fraction: 14.6%
Fine fraction: 85.4%
Feng B 2020For a sampling of isolation room air, a NIOSH sampler was placed on a tripod
1.2 m in height and 0.2 m away from the bed at the side of the patient’s head.
The sampling duration was 30 min, and a total of 105-L room air was sampled. (9
Exhaled Breath (EB) samples, 8 Exhaled Breath Condensate (EBC) samples, and
12 bedside air samples)
RNA was detected in the air
sample in <1 μm and >4 μm
fractions,
Hernández JL
2020
Air was sampled in three areas: Emergency area (Clinic A), Internal medicine
(Clinic A), COVID 19 patient area (Clinic A), and COVID-19 patients care room
(Clinic B). Sampling in all areas was accomplished in 3 h. Filters of 25 mm
diameter with 0.22 μm pores were utilized (Millipore, AAWP02500), placed in a
sterilized filter holder (Millipore, SWINNX) coupled to a vacuum system through a
previously disinfected plastic hose, filtering the air with a flow of 9.6 L/min in each
filter holder.
Filtration through 0.22 μm pores.
Kayalar O
2021
A total of 155 samples were collected daily using various PM samplers in each
city.Samples were collected on glass fiber filters (GF) and Teflon filters (TF) with
different sampling equipment
Samplers: SKC filter sampler; dichotomous PM sampler; high volume air sampler;
low volume stack filter; Zambelli PM sampler; High volume cascade sampler
The PM sizes of positive samples
were PM<0.49 (n = 1), PM0.49-0.95
(n = 1), PM0.95-1.5 (n = 1), and PM>7.2
(n = 2).
Lednicky JA
2021
The Sioutas Personal Cascade impactor sampler (PCIS) separates airborne
particles in a cascading fashion and simultaneously collects the size-fractionated
particles by impaction on polytetrafluoroethylene (PTFE) filters). It has collection
filters on four impaction stages (A–D), and an optional after-filter can be added
to a 5th stage (E). The PCIS separates and collects airborne particulate matter
above the cut-point of five size ranges: >2.5 μm (Stage A), 1.0–2.5 μm (Stage B),
0.50–1.0 μm (Stage C), 0.25–0.50 μm (Stage D), and (Stage E) <0.25 μm (collected
on an after-filter).
PCIS filter A Cq value: 36.66
PCIS filter B: 35.23
PCIS filter C: 34.37
PCIS filter D: 33.50
PCIS filter E <0.25: 40.1
Linde KJ 2022In every patient room, 6-hr inhalable dust samples were taken using a filtration-
based technique at all three locations (Conical Inhalable dust Sampler (CIS),
JS Holdings, UK). In addition, one 6-hr two-stage cyclone-based sample with
filter back-up was positioned near the feet of the patient when bedridden or
at 1.5 meters from the chair of the patient (NIOSH BC 251,), as well as a 1-hr
impingement-based sampler positioned in proximity of the head of the patient
(5ml BioSampler, SKC, UK) The filtration-based sampler was equipped with a
37mm diameter 2.0μm pore-size Teflon filter. The two-stage cyclone-based
sampler allowed size-selective sampling and was equipped with two conical tubes
(of 15 ml and 1.5 ml), which sample respectively particulates of 1–4μm and >4μm,
and a backup Teflon filter (37 mm diameter 2.0 μm pore-size Pall incorporated,
Ann Arbor, USA) for particulates of <1μm when operated at a flow of 3.5L/min.
>4 μm: 60%
1–4 μm 50%
<1 μm 20%
Inconclusive and positive results
were more frequently present in
the largest particle size fraction,
Liu Y & Ning Z
2020
Over a 2-week period: 30 aerosol samples of total suspended particles collected
on 25-mm-diameter filters loaded into styrene filter cassettes (SKC) by sampling
air at a fixed flow rate of 5.0 l min−1 using a portable pump (APEX2, Casella).
Three size-segregated aerosol samples were collected using a miniature cascade
impactor (Sioutas Impactor, SKC) that separated aerosols into five ranges
(>2.5 μm, 1.0 to 2.5 μm, 0.50 to 1.0 μm and 0.25 to 0.50 μm on 25-mm filter
substrates, and 0 to 0.25 μm on 37-mm filters) at a flow rate of 9.0 l min−1. Two
aerosol deposition samples were collected using 80-mm-diameter filters packed
into a holder with an effective deposition area of 43.0 cm2; filters were placed
intact on the floor in two corners of an ICU for 7 days.
SARS-CoV-2 aerosols, one in
the submicrometre region (dp
between 0.25 and 1.0 μm) and
the other in supermicrometre
region (dp > 2.5 μm). Aerosols in
the submicrometre region were
found with peak concentrations
of 40 and 9 copies m3 in the
0.25–0.5 μm and 0.5–1.0 μm
range, respectively. By contrast,
aerosols in the supermicrometre
region were mainly observed in
the PPAR of zone C of Fangcang
Hospital with concentrations of 7
copies/m3
Lotta-Maria
AH 2021
"Seven different air collection methods were used.
A Dekati PM10 cascade impactor (20 l/min air flow) with three stages (>10, >2.5,
and >1 µm), The impaction stages of PM10, PM2.5, and PM1 were fitted with
25-mm-diameter cellulose acetate membrane filters (CA filter, GE Healthcare Life
Sciences) and the backup plate with a 40-mm C The BioSpot 300p bioaerosol
sampler prototype (Aerosol Devices Inc.)
As a more portable solution for personal area air sampling, a standard 25-mm
gelatin (Sartorius Stedim Biotech) or mixed cellulose ester (MCE) filter equipped
in the Button sampler with a Gilian 5000 air sampling pump, 4 l/min airflow, and a
porous curved surface inlet was used Three Andersen cascade impactors (400 W
pump and 28.3 l/min flow rate) were used simultaneously
a Dekati eFilter was used in two collections.
SARS-CoV-2 RNA was detected
in the following particle sizes:
0.65–4.7 µm, >7 µm, >10 µm, and
<100 µm.
Mallach G
2021
Aerosol (small liquid particles suspended in air) samples were collected onto
gelatin filters by Ultrasonic Personal Air Samplers (UPAS) fitted with <2.5μm
(micrometer) and <10 μm size-selective inlets operated for 16 hours (total
1.92m3), and with a Coriolis Biosampler over 10 minutes (total 1.5m3).
RNA samples were positive in
9.1% (6/66) of samples obtained
with the UPAS 2.5μm samplers,
13.5% (7/52) with the UPAS
10μm samplers, and 10.0%
(2/20) samples obtained with the
Coriolis samplers.
McGain F 2020Two spectrometers to measure aerosol particles: the portable Mini Wide Range
Aerosol Sizer 1371 (MiniWRAS) and the Aerodynamic Particle Sizer (APS). During
the procedure, the aerosol detector inlet was positioned 30 cm directly above the
patient’s neck, representing the surgeon’s breathing air space
APS detected larger aerosols
(> 0.37 mm) and MiniWRAS
smaller particles (0.01–0.35 mm).
Nannu
Shankar S
2021
Using polytetrafluoroethylene (PTFE) filters and a VIable Virus Aerosol Sampler
(VIVAS), (2) size-fractionated particles in aerosols according to aerodynamic size
using a 2-stage cyclone aerosol sampler (NIOSH bioaerosol sampler, BC-251)
and a Sioutas personal cascade impactor sampler (PCIS), The PCIS was used with
a Leland Legacy pump and operated at a flow rate of 9 L/min for 90 min. PTFE
filters (25 mm, 0.5 μm pore) were used to collect particles of size >2.5 μm, 1–2.5
μm, 0.5–1 μm and 0.25–0.5 μm in the 4 collection stages.
virus-associated particles
were >0.25 μm and >0.1 μm
respectively
Ong SWX 2021Air samples were collected using a BioSpot-VIVAS BSS300-P bioaerosol sampler
(Aerosol Devices, Fort Collins, CO), which collects airborne particles using a water-
vapor condensation method into a liquid collection medium at a flow rate of 8 L
per minute.
SARS-CoV-2 nucleic acid was
detected in aerosols <1 µm,
1–4 µm, and >4 µm in diameter.
Passos RG
2021
Two types of aerosol samples in indoor environments were collected: (1) aerosol
samples of suspended particles using air samplers with filters, in order to
quantify the concentrations of SARS-CoV-2 in aerosols and to estimate the size
of airborne particulates. In this case, the lower limit was estimated by the filter
porosity and the upper limit defined by a cyclone separator (<4 μm at a flow rate
of 2.5 L min−1; or with no cyclone, no upper size limit), and/or by approximate
comparison between results of sampling with different filters (pore sizes), at the
same location; and (2) aerosol deposition samples, in order to determine the
deposition rate of airborne SARS-CoV-2.
Air samples tested positive for
SARS-CoV-2, in particle sizes
>4 μm and 1–4 μm in diameter.
Samples from the fractionated
size <1 μm were all negative in
that study, as were all
non-size-fractionated PTFE filter
cassette samples (3 μm pores).
Semelka CT
2021+
Viral transport media (VTM) on sedimentation plates from Anderson air samplers
were pooled from stages 1 and 2 (filter sizes ≥5 μm) and stages 3–6 (filter sizes
<5 μm) to separate large droplets from aerosols.
Viral particles in large respiratory
droplets were recovered adjacent
to the head from 2 of 26 patients
(8%; droplet sizes ≥5 μm) who
were closer to symptom onset
(2 and 4 days). No aerosol-
sized particles were detected
in air samplers for masked or
unmasked runs.
Santarpia JL
2020a
Air samplers were placed in various places in the vicinity of the patient, including
over 2m distant. Personal air sampling devices were worn by study personnel
for two days during sampling. Measurements were made to characterize the
size distribution of aerosol particles, and size-fractionated aerosol samples were
collected to assess the presence of infectious virus in particle sizes of >4.1 µm,
1–4 µm, and <1 µm in the patient environment. An Aerodynamic Particle Sizer
Spectrometer was used to measure aerosol concentrations and size distributions
from 0.542 µm up to 20 µm. A NIOSH BC251 sampler18 was used to provide size
segregated aerosol samples for both rRT-PCR and culture analysis.
Two of the 1–4 µm samples
demonstrated viral growth,
between 90% and 95%
confidence
Stern RA 2021
(a)
"Cascade samplers were located at floor height: (1) outside the entrance
to a COVID-19 ward (CW1); (2) in personal protective equipment (PPE) donning
room outside the entrance to another COVID-19 ward (CW2); (3) outside the
entrance to the medical intensive care unit (ICU); (4) at a staff workstation in the
emergency department (ED); and (5) at a nursing staff workstation of a ward not
designated for the care of COVID-19 patients
In total 8 samples were positive:
2 for Fine (≤ 2.5 μm) particles
and 3 each for Coarse (10.0–2.5 μm)
and Large (> 10.0 μm)
Stern RA 2021
(b)
The study used custom-designed Harvard Micro-Environmental Cascade
Impactors (Demokritou et al., 2002) to collect simultaneous samples in three
distinct size fractions: fine (≤2.5 μm aerodynamic diameter), coarse (2.5–10 μm),
and large (≥10 μm)
In total 13 samples were positive:
3 for Fine (≤ 2.5 μm) particles
and 7 for Coarse (10.0–2.5 μm)
and 3 for Large (> 10.0 μm). The
proportion of samples found
positive was greatest for the
symptomatic patient rooms (6/24
samples or 25%) with the highest
viral concentration in these
rooms (25 copies/m3)
Zhang X 2022Aerosols of 0.5 to 10 μm in diameter were collected using SASS 2300 Wetted Wall
Cyclone Samplers (Research International, Inc. Monroe, WA, USA) operating at a
flow rate of 325 liters per minute (L/min)
Aerosol particles of 0.5 to 10 μm
in diameter were detected

We found 69 different descriptions of air samplers deployed: the two most frequently used samplers were the MD8 sampler, Sartorius, Goettingen, Germany (n=12 studies) and the National Institute for Occupational Safety and Health (NIOSH) Aerosol sampler (n=10 studies). Several studies used different methods, and there were variations in the flow rate used and associated methods that affect sampling techniques (see Extended data: Appendix 510).

Hospital/Health Center. There were 90 studies conducted in healthcare settings: Of these, 362/3079 air samples in hospital ward environments from 75 studies (median 8%, IQR=0% to 23%) and 74/703 (median 17%, IQR=0% to 38%) air samples in the ICU setting from 23 studies reported RT-PCR positive results. (See Figure 3).

9ad1e537-1b7b-4130-8ba5-352576faa348_figure3.gif

Figure 3. Proportion and distribution of SARs-CoV-2 RT-PCR positive Air samples in Hospitals and Intensive Care Unit (ICU) environments (n=80 studies).

Twenty studies reported sampling results in the hospital environment (non-ICU) and the ICU. Figure 4 shows that ICU environments were approximately twice as likely to detect SARS-COV-2 RNA in air samples, OR 2.07 (95% CI, 1.23 - 3.47, I2 =0%, n = 20 studies, 1300 air samples).

9ad1e537-1b7b-4130-8ba5-352576faa348_figure4.gif

Figure 4. Forest plot showing the risk of presence of positive air samples of SARS-CoV-2 in hospitals.

We found eleven studies conducting air sampling both in hospitals and in other environments. Ben-Shmuel et al. sampled within the hospital environment and in a quarantine hotel. Lotta-Maria et al. sampled the air and surfaces from the surroundings of 23 hospitals and eight home-treated patients. Ma J 2020 et al. reported on an unventilated quarantine hotel toilet room from 26 samples taken and Moharir SC 2022 et al. sampled in hospital, the ICU and in patients’ homes. Ong SWX 2021 et al. reported air samples from airborne-infection isolation rooms and a community isolation facility housing COVID-19 patients. Stern RA 2021 (b) et al. sampled 30 locations in a hospital and also a COVID-19 quarantine facility.

Liu Y & Ning Z 2020 et al. reported 4/13 public areas were RT-PCR positive; Zhang D 2020 et al. sampled the outdoor environment of three hospitals. Mallach G 2021 et al. sampled in rooms with COVID-19 positive patients and in long term care homes. Similarly, Mouchtouri VA 2020 et al. sampled a hospital, a nursing home, and Long-Term Care Facility, but also included a ferryboat. Passos RG 2021 et al. reported environmental and hospital air sampling from May to August 2020.

Masoumbeigi H 2020 et al. sampled in a military hospital. Lednicky JA 2020(b) et al. sampled in a respiratory infection evaluation area of a student healthcare centre and reported one positive sample with a CT of 39 (virus genome equivalent of 0.87 virus genomes L–1 air).

Four studies reported on Exhaled Breath Condensate (EBC). Ma J 2020 et al. reported 14/52 EBC samples as RT-PCR positive and Feng B 2020 et al. reported 2/8 positive EBC samples. Zhou L 2020 et al. collected samples of exhaled breath of patients ready for discharge and air samples. Adenaiye OO 2021 et al., sampled in a university campus and in the community and collected 30-minute exhaled breath samples while vocalizing into a Gesundheit-II sampler.

Community. Thirty-eight studies reported data in the community and did not sample in hospitals (see table of characteristics and Figure 1). Eight were done outdoors and/or in the community [Chirizzi D 2020, Kayalar O 2021, Kwon KS 2020, Linillos-Pradillo 2021, Pivato A 2021, Ramuta MD 2022, Setti L 2020, Dziedzinska R 2021]; five studies sampled buses [Di Carlo P 2020, Hoffman JS 2020, Luo K, 2020, Shen Y 2020 and Moreno T 2020 that also included sampling in subway trains). Four studies sampled in student rooms or university buildings [Adenaiye OO 2021: university campus and community; Pan J 2022: student rooms; Zhang X 2022: non clinical areas of University buildings and Lednicky JA 2020b: a student Healthcare centre.

Three studies sampled apartments/blocks of flats [Lin G 2020, Kang M 2020 and Nannu Shankar S 2021] and three nursing homes [De Man P 2020, Dumont-Leblond N 2021, Linde KJ 2022]. Two studies each sampled choir practices [Charlotte N 2020, and Hamner L 2020]; meat processing plants [de Rooij MMT 2021 and Günther T 2021]; restaurants [Li Y & Qian H 2020 and Lu J 2020]; quarantined households [Dohla M 202 and Horve PF 2021] that also included an isolation dormitory.

Seven studies sampled one setting each: a car [Lednicky JA 2021]; dental clinics [Bazzazpour S 2021]. an employee building [Li X 2022], a fitness centre [Li H 2021] a home residence [Wong JCC 2020] an indoor community setting [Conte M 2021] and a wastewater treatment plant [Gholipour S 2021].

Viral culture. Twenty-six studies attempted viral culture [Adenaiye OO 2021, Ang AX 2021, Ben-Shmuel 2020, Binder 2020, Coleman KK 2021, Dohla M 2020, Dumont-Leblond N 2020, Hu J 2020, Kotwa 2021, Lednicky JA 2020a, Lednicky JA 2020b, Lednicky 2021, Li X 2022, Linde KJ 2022, Lotta-Maria AH 2021, Mallach G 2021, Moharir SC 2022, Nannu Shankar S 2021, Nissen K 2020, Ong SWX 2021, Pan J 2022, Ruffina de Sousa 2022, Santarpia JL 2020a, Santarpia JL 2020b, Winslow R 2021, Zhou J 2020]. In 18 of these studies, infectious virus could not be isolated and cytopathic effects could not be observed [Ang AX 2021, Ben-Shmuel 2020, Binder 2020, Coleman KK 2021, Dohla M 2020, Dumont-Leblond N 2020, Hu J 2020, Kotwa 2021, Li X 2022, Lotta-Maria AH 2021, Mallach G 2021, Nissen K 2020, Ong SWX 2021, Pan J 2022, Ruffina de Sousa 2022, Santarpia JL 2020b, Winslow R 2021, and Zhou J 2020] (see Table 6).

Table 6. Live culture results (n =26).

Study
(n=64)
SettingMethodAir Samples positive
n/d for SARs-CoV-2
RNA
Live cultureNotes
Adenaiye
OO 2021
University
campus and
community
COVID-19 cases series. Fomite
(phone) swabs, and 30-minute
exhaled breath samples
No mask
coarse = 15/78
fine = 22/78
With mask
coarse = 10/71
fIne = 14/71
No mask
coarse = 0/38
fIne = 0/75
Mask
coarse = 0/16
fine = 2/66
None of the fine-aerosol samples collected while not wearing
face masks were culture-positive. Two exhaled breath samples
and fine-aerosol samples collected from participants while
wearing face masks were culture-positive.
Ang AX
2021
HospitalAir and surface samples were
collected from one isolation ward
and two open-cohort wards housing
laboratory-confirmed COVID-19
patients
13/270/27High-flow rate air samplers, which provided higher sensitivity
in detecting environmental SARS-CoV-2 in air when conducting
surveillance in such indoor settings.
Ben-Shmuel
2020
hospital &
quarantine
hotel.
Surface and air sampling at two
COVID-19 isolation units and in a
quarantined hotel.
2/6
quarantine hotel 1/1
0/3Relatively high CT values (>34) in the samples.
Binder 2020HospitalAn observational case series of
20 patients hospitalized with
coronavirus disease
3/195 samples from 3
patients
0/3 viable virus
Coleman KK
2021
HospitalExhaled breath emitted by COVID-19
patients
13/22 participants
25/66 samples
0/13 participants
0/25 samples
Overall viral RNA loads were relatively low, they differed
significantly between breathing, talking, and singing,
Dohla M
2020
Quarantined
households
An observational study of 43
adults and 15 children living in 21
households; air (also surface and
wastewater) samples taken.
0/15Infectious virus could
not be isolated.
26/43 adults were positive for RT-PCR. 10/ 66 wastewater
samples and 4/119 surface swab samples were RT- PCR positive
Dumont-
Leblond N
2020
HospitalAn observational study in acute care
hospital rooms over the course of
nearly two months
11/100 from 6 patient
rooms
Viral cultures were
negative
Hu J 2020HospitalAn observational study: indoor and outdoor air
samples in ICUs and CT
rooms
8/38 ICUs
1/6 CT rooms
Samples from medical
staff rest areas and
corridors were all
negative (denominator
not clear)
All positive aerosol
samples were
negative
5/24 surface swabs in the ICU were PCR positive. After
rigorous disinfection, no viral RNA was detected in a second
batch sample from the same places. Positive rates for the
mask samples were relatively high compared with the aerosol
or surface samples.One mask from a critically ill patient was
positive.
Kotwa, 2021HospitalAir and surfaces samples in rooms of
COVID-19 patients
3/1460/3The three positive air samples were taken from 3 different
rooms at 1 m from the patient
Lednicky JA
2020a
HospitalObservational: air samples were
collected, and virus culture
attempted
4/4 air samples without
a HEPA filter
0/2 samples using a
HEPA filter
Virus-induced CPE
was observed for
4/4 RNA-positive air
samples.
Plaque assays could not be performed due to a nationwide
nonavailability of some critical media components (due
to COVID-19 pandemic-related temporary lockdown of
production facilities), so TCID50 assays were performed in
Vero E6 cells to estimate the percentage of the collected virus
particles that were viable. Estimates ranged from 2 to 74
TCID50 units/L of air
Lednicky JA
2020b
Student
Healthcare
centre
Observational, air samples collected,
and virus culture attempted
1/2 air samplesGeneral virus-induced
cytopathic effects
were observed within
two days post-
inoculation
PCR tests for SARS-CoV-2 vRNA from cell culture were negative.
Three respiratory viruses were identified using the Biofire RVP:
Influenza A H1N1, Influenza A H3N2, and Human coronavirus
OC43
Lednicky JA
2021
Car Journey SARS-CoV-2 in a car driven by a
COVID-19 patient. The PCIS sampler
was attached to the sun-visor on
the passenger side of the car,
approximately 3 feet from the
patient’s face and with the intake
port pointing toward the roof of the
car, with the pump assembly placed
on the front passenger seat.
4/51/4The Cq of the culture positive sample was 29.65 days post-
inoculation of Vero E6 cells. A Cq value of 12.46 was attained
3 days post-inoculation of the cells.The patient had minimal
symptoms, and no viral concentration or infectiousness was
established. The sampler was approximately 3 feet from the
patient’s face.
Li X 2022Employee
building
COVID-19 outbreak with two
fast food employees infected,
using environmental sampling,
epidemiological tracing, viral RNA
sequence, and surveillance method.
3/20
female washrooms n=2
0/3
Linde KJ
2022
Nursing homesAir samples were collected at three
locations in the patient’s room: 1)
near the head of the patient within
approximately 0.5 metres of the
patient, 2) near the feet of bedridden
patients, approximately 1.5 meters
from the head or approximately
1.5 meters from mobile patients
sitting in a chair, and 3) near the
location often used by healthcare
workers more than 2 meters away
from the patient such as the sink, all
positioned at 1.5m height.
Total: 94/213
Positive Oropharyngeal
Swab (OPS) 93/184
Negative OPS 1/29
7/259 settling dust
samples in three wards
1/10All four air sampling techniques detected SARS-CoV-2 RNA and
showed high rates of positivity in the rooms of patients with
positive OPS
CPE was observed in three OPS and one active air sample and
confirmed by immunofluorescent staining.
The active air sample from the CDC-NIOSH sampler (>4µm size
fraction) had the lowest Ct of all environmental samples (29.5)
and was from the room of the patient with the lowest OPS
Ct-value (19.8).
There was no information on the distance of the positive
culture. However, the study reports that ‘ultra-fine particles
(<1μm), which can travel further, do not seem to be the key
vehicle of SARS-CoV-2 transmission. The vast majority of
settling dust and surface swab samples from common areas
were negative, suggesting SARS-CoV-2 transmission is more a
local phenomenon than widespread.’
Lotta-Maria
AH 2021
Hospital &
Home
Air and surface samples from the
surroundings of 23 hospitalized
and eight home-treated COVID-19
patients
33/259
(12/29 air collections)
0/33Seven different air collection methods were used.
Mallach G
2021
Hospital &
Long term care
home
Particulate air sampling in rooms
with COVID-19 positive patients in
hospital ward ICU rooms, long-term
care homes and a correctional
facility experiencing an outbreak.
ICU 4/23
Ward 7/92
LTC 3/15
Correctional facility 1/8
0/15
Moharir SC
2022
Hospital &
homes
Air, samples from different locations
occupied by coronavirus disease
(COVID-19) patients
Total 45/115
Hospital 40/80
(ICU 10/220
Closed rooms 5/17
homes 10/18
1/3 from the home
setting
No details are provided for the culture results and no details
on the viral concentrations beyond ‘that had relatively lower Ct
values’
Nannu
Shankar S
2021
ApartmentsAir and surfaces in bedrooms
of two 20-year-old persons with
symptomatic COVID-19 were
sampled as self-isolating persons.
Volunteer A
NIOSH 1/3
PTFE 0/3
Volunteer B
NIOSH 4/6
PCIS 4/10
volunteer B
Oct 2 4/8
Oct 6 0/8
Volunteer B was co-infected with HAdV B3, which outgrew
SARS-CoV-2 in our Vero E6 cells. Adenovirus B3 causes acute
respiratory infections and likely contributed to the respiratory
symptoms experienced by volunteer B.
Nissen K
2020
HospitalObservational: surface swabs and
fluid samples were collected, and
experimental: virus culture was
attempted.
7/19 filters
11 days later, 4/19
positive for both
genes.
No significant CPE
after three passages
on Vero E6 cells
Ct values varied between 35.3 and 39.8 for the N and E genes.
Virus culture was attempted: RNA was detected in sequential
passages, but CPE was not observed.
Ong SWX
2021
Hospital &
Community
Air samples from airborne-infection
isolation rooms and a community
isolation facility housing COVID-19
patients
6/120/6Virus cultures were negative after 4 blind passages.
Pan J 2022Student roomsSurface swab samples and heating,
ventilation, and air conditioning
(HVAC) filters from 24 rooms
occupied by students positive for
COVID-19,
15/21 HVAC
4/6 bathroom exhaust
grilles
Cultured those with
a Ct value < 33, and
none contained
culturable virus.
No denominator for viral culture supplied
Ruffina de
Sousa 2022
HospitalAir samples from rooms occupied
by COVID-19 patients in a major
hospital.
patient rooms 9/22;
adjoining anterooms
10/22
PFU recovery
patient room 3/9;
anteroom 8/10
Average Ct: patient rooms 38.3 and anterooms 38.3
Infectious viruses could not be isolated in Vero E6 cells from
any environmental sample.
Santarpia JL
2020a
HospitalObservational: size-fractionated
aerosol samples collected;
experimental: virus culture was
attempted.
6/6 patient rooms.In 3 aerosol samples
(<1 μm), cell culture
resulted in increased
viral RNA.
The presence of SARS-CoV-2 was observed via western blot for
all but one of the samples (<1 um, with statistically significant
evidence of replication, by rRT-PCR (Figure 2). The intact virus
was observed via TEM in the submicron sample from Room.
Viral replication of aerosol was observed in the 1 to 4 μm size
but did not reach statistical significance.
Santarpia JL
2020b
Healthcare
centre
Observational: high-volume (50 Lpm)
and low-volume (4 Lpm) personal
air samples (& surface samples)
collected from 13 Covid-19 patients;
experimental: virus culture was
attempted.
63% of in-room air
samples were positive
(denominator unclear)
Due to the low
concentrations
recovered in the
samples, cultivation
of the virus was not
confirmed in these
experiments. *
Partial evidence of virus replication from one air sample. In the
NBU, for the first two sampling events performed on Day 10,
the sampler was placed on the window ledge away from the
patients and was positive for RNA (2.42 copies/L of air). On Day
18 in NBU Room B, occupied by Patient 3, one sampler was
placed near the patient, and one was placed near the door
greater than 2 metres from the patient’s bed while the patient
was receiving oxygen (1L) via nasal cannula. Both samples
were positive by PCR, with the one closest to the patient
indicating a higher airborne concentration of RNA (4.07 as
compared to 2.48 copies/L of air).
Winslow R
2021
HospitalProspective observational study
of 30 low SATS Covid-19 cases
who received either supplemental
oxygen, CPAP or HFNO
4/901/51 nasopharyngeal
sample
One nasopharyngeal sample from an HFNO participant (E
gene Ct 21.99) could demonstrate the presence of viable
(infective) virus
All other samples, including environmental samples, were
negative. Samples were either positive or suspected positive
for viral RNA and were cultured.
Zhou J 2020HospitalObservational: (air & surface)
samples collected from a hospital
with a high number of Covid-19
inpatients.
2/31 air samples
positive
12/31 suspected
0/14We defined samples where both of the PCRs performed from
an air or surface sample detected SARS-CoV-2 RNA as positive,
and samples where one of the two PCRs performed from an
air or surface sample detected SARS-CoV-2 RNA as suspected

Of the remaining eight studies, Adenaiye OO 2021 found culture-positive SARS-CoV-2 from two exhaled breath samples from participants while they were wearing face masks. None of the fine aerosol samples collected when the participants were not wearing face masks tested positive on culture.

Lednicky JA 2020b reported that general virus-induced cytopathic effects were observed within two days post-inoculation. The amount of virus present in 390 L of sampled air was very low (approximately 340 virus genome equivalents). RT-PCR for SARS-CoV-2 RNA from the cell cultures were negative, but three other respiratory viruses were identified: Influenza A H1N1, Influenza A H3N2, and human coronavirus OC43.

Lednicky JA 2020a observed presumed virus-induced CPE for 4/4 RNA-positive hospital air samples. The authors report that plaque assays could not be performed due to a nationwide non-availability of some critical media components in the United States. They also report that it took 6 to 11 days post-inoculation before rounding of the cells was observed with material collected by the air sampler and there is no report of a serial subculture of the positive air samples to demonstrate propagation of a competent replicating virus.

Lednicky JA 2021 reported positive culture in one out of four samples collected from inside a car driven by a SARS-CoV-2 positive patient. The passenger was sitting approximately 3 feet from the sampler.

Linde KJ 2022 reported positive cultures in one out of 10 air samples taken from the rooms of patients who were SARS-CoV-2 positive. The authors did not specify the distance from the patient from where the sample was collected.

Moharir SC 2022 reported positive cultures in one out of three air samples taken from the homes of patients who were SARS-CoV-2 positive. The authors did not specify the distance from the patient from where the sample was collected.

Nannu Shankar S 2021 reported positive culture in four out of 16 air samples taken from the home of a patient who was SARS-CoV-2 positive. However, the patient was co-infected with HAdV B3, which outgrew SARS-CoV-2 in Vero E6 cells. The authors stated that adenovirus B3 likely contributed to the respiratory symptoms experienced by the patient.

Santarpia JL 2020a reported 3/39 aerosol samples (particle size <1 μm) that cell culture resulted in increased SARS-CoV-2 RNA at very low levels. A virus-like particle was observed via transmission electron microscopy in the submicron sample from one room. This study was published as a preprint (checked 5 March 2021) and is subject to methodological criticisms. Serial RT-PCR of cell culture supernatant was unclear and incongruent with the statement that some increase in viral RNA may have occurred. No size-fractionation techniques were used to determine the size range of SARS-CoV-2 droplets and particles.

Table 7 sets out several methodological issues relating to viral culture).

Table 7. Methodological issues in viral culture studies.

StudyMethodological
Adenaiye OO
2021
  •   Logistical considerations required freezing samples between collection and culture, with the potential loss of
infectiousness.
  •   Used a Gesundheit-II (G-II) exhaled breath sampler does not necessarily represent the real-world situation as
samples are collected directly from patients, not the environment
Ang AX 2021  •   Sample collection and subsequent analysis were subject to the availability of the trained medical staff, consent of
patients, and the capacity of the BSL-3 processing laboratory.
Ben-Shmuel
2020
  •   There was a delay between the onset of symptoms and the actual sampling in patients' rooms. Therefore, at the
time of sampling, these patients might not have shed viable virus,
Binder 2020   •   This study separated particles by three sizes: >4 µm, 1-4 µm, and <1 µm and used multiple sampling sites which
is a robust sampling methodology.
  •   The median day’s post symptom was reported as 10 with a range of 1 to 34 days, and only one patient had a
cycle threshold for the N gene < 20. This limits the finding of any cultivatable virus and the conclusions.
Coleman KK
2021
  •   Used a Gesundheit-II (G-II) exhaled breath sampler (see Adenaiye 2021)
  •   Low viral load in the samples compared with those generally found in culturable clinical samples. Sampling
methodology yielded viral RNA loads below 103.8 genome copies per sample,
Hu J   •   All positive masks were subject to cell culture and inoculated with Vero-E6 cells after blind passage for three
generations which is a robust approach.
  •   One mask from a critically ill patient was positive for the virus but no details on which passage and at what
quantitative burden.
  •   The masks could have been contaminated by saliva or nasal secretions and the conclusion stated that masks
blocked the release of viable virus in the air exhaled from the patient cannot be confirmed.
Kotwa, 2021  •   The median time between the onset of illness and air sampling was 11 days (IQR, 7–14); the time between the
onset of illness and sampling date for all 3 PCR-positive air samples was 4 days.
  •   Air samples were excluded from the genomic sequence analyses due to poor quality sequences.
Lednicky 2020a  •   it is not clear why plaque assays could not be performed due to a nationwide nonavailability of some critical
media components in the US. Three serial 3-hr air samplings were performed.
  •   Over the 9 hours, patients likely would have moved about and may have been close to the samplers. The
method does not mention particle sizing for the sampler (ie < or > 5 microns ) and the sampled particles could
be any size hence it is difficult to state they were true aerosols.
  •   No data are provided about health workers who may have been in the room and might have handled the air
samplers.
  •   Samples were not done at 0.5 m to 1 metre to see if there was a gradient effect. It was noted it took 6 to 11 days
post-inoculation before rounding of the cells with material collected by air sampler and there is no report of a
serial subculture of the positive air samples to demonstrate propagation of a healthy and propagating virus.
  •   Nothing is presented about testing the air sampling isolates in susceptible animal models.
Lednicky JA
2020b
  •   Estimated concentration of 0.87 virus genomes L–1 air. The amount of virus present in 390 L of sampled air was
low (approximately 340 virus genome equivalents).
  •   The PCR tests for SARS-CoV-2 vRNA from cell culture were negative, highlighting the essential requirement to
test for other pathogens when general virus cytopathic effects are observed.
  •   Three respiratory viruses were identified: Influenza A H1N1, Influenza A H3N2, and Human coronavirus OC43
Lednicky JA
2021
  •   Two days after the diagnostic sample was obtained, the patient agreed to have the PCIS placed in her car (an
older model Honda Accord) for the drive from the clinic to her home.
  •   The PCIS was attached to the sun-visor on the passenger side of the car, approximately 3 feet from the patient’s
face and with the intake port pointing toward the roof of the car, with the pump assembly placed on the front
passenger seat. During the 15-min drive, the patient was not wearing a mask.
  •   Early CPE consistent with SARS-CoV-2 were observable by 3 days in cells inoculated with material collected onto
PCIS filter D; by day 5, foci of infection were apparent for cells inoculated with material from filter D, with no
signs of virus infection in cells inoculated with material collected by PCIS filters B, C, and E.
  •   For further confirmation, an aliquot (20 μL) of the virus collected 5 days post-inoculation of material from filter D
was passaged in Vero E6 cells, wherein an rRT-PCR Cq value of 12.46 was attained 3 days post-inoculation of the
cells.
Li X 2022  •   Two air samples collected on Dec. 20 and 21 from the female washroom without ventilation even after the
disinfection were positive for SARS-CoV-2 with an estimated concentration level of 5640–7840 SARS-CoV-2 RNA
copies m–3
Linde KJ 2022  •   Among the 78 positive OPS, cyclone-based samples, impingement-based samples, surface swab samples, 44
had an RdRp Ct-value ≤35 and were investigated by virus culture.
  •   CPE was observed in three OPS and one active air sample and confirmed by immunofluorescent staining.
  •   The active air sample from the CDC-NIOSH sampler (>4µm size fraction) had the lowest Ct-value of all
environmental samples (29.5) and was from the room of the patient with the lowest OPS Ct-value (19.82).
  •   If the virus-induced cytopathic effect was observed, immunofluorescent detection of nucleocapsid proteins was
performed to confirm the presence of SARS-CoV-2
  •   Limited information on the virus culture was reported
Lotta-Maria AH
2021
  •   Seven different air collection methods were used.
  •   Only conducted environmental sampling at a single time point.
Mallach G 2021  •   were careful to always sample two or more meters from COVID-19 patients, to ensure detection of the virus only
at distances traditionally considered to be consistent with the airborne transmission.
  •   The mean Ct values were just over and under 34 for the N and E proteins, respectively. The Ct value was <34 for
the N protein in only one room, and <34 for the E protein in eight rooms
  •   No direct sampling of patients was performed to determine their infectiousness, and we did not have access to
patient history
  •   Almost all hospitalized patients were admitted at least five days after symptom onset, when they are less likely to
be shedding infectious virus,
Moharir SC
2022
  •   Many of the air samples from hospitals and closed room experiments showed PCR signal for one of the SARS-
CoV-2 genes or had very high Ct values.
  •   No details on culture results or on samples beyond the three from the home setting
Nannu
Shankar S 2021
  •   "Virus-induced CPE were observed in Vero E6 cells inoculated with air and surface samples collected from
volunteer B’s room within 4 days of their inoculation. Since the Cq value was high (>34) when nucleic acids
extracted from the cell growth media of the cell cultures were tested by RT-qPCR for SARS-CoV-2.
  •   The study authors suspected an additional respiratory virus was present, as previously observed in Lednicky
et al., 2020b and Pan 2017)
  •   Volunteer B was co-infected with HAdV B3, which outgrew SARS-CoV-2 in our Vero E6 cells. Adenovirus B3
causes acute respiratory infections and likely contributed to the respiratory symptoms experienced by volunteer
B.
  •   There was an Inconsistent use of samplers and no measurements on aerosol size distribution.
Ong SWX 2021  •    Selected patients early in their illness course and with a lower Ct value because they hypothesized this would
maximize the possibility of successfully isolating viable viruses.
  •   Most patients had only mild disease,
  •   Sampling was conducted in a naturally ventilated community isolation facility, and airborne-infection isolation
hospital rooms (designed to limit transmission of airborne infections)
Pan J 2022  •   Viral load estimates were made by extrapolating information on the amount of RNA found on the rooms' HVAC
filters.
  •   Results suggest that SARS-CoV-2 decays within the amount of time between the student vacating the room and
sampling in this study (ranging from 6 h to 4 days).
Ruffina de
Sousa 2022
  •   Patients were entering their second week of the disease, and SARS-CoV-2 titers in the upper respiratory tract
tend to peak in the first week of disease - Median days since onset (IQR) 11.5 (7–14)
  •   No CPE was observed
  •   Average Ct in the patient rooms 38.3 and anterooms 38.3 was too high for viable viral culture
Santarpia JL
2020a and b
  •   For Santarpia 2020 (a) we could only find a preprint publication. A large number of samples were collected.
Serial PCR of cell culture supernatant was unclear and incongruent with the statement that some increase in
viral RNA may have occurred. Increased viral RNA presence is a surrogate and subject to many interpretations
and should not be considered equal to the cultivation of replication and infection competent virus on cell culture
which was not identified. Western blot assay was not done in cell supernatant samples with non-statistically
significant evidence of replication, which would have acted as a control to ensure the findings were not spurious.
Western blots are very weak, with no positive control or size markers and the signal doesn't necessarily come
from a replicating virus, there's no "before culture" analysis.
  •   The presence of virus-like particles on TEM is not proof that these are replicating viruses or necessarily even
SAR-CoV-2. No comparisons to control TEM photomicrographs of the live virus from fresh Vero cells are
presented to discuss.
  •   No information is provided about activity by either patients or the doffing by health workers which may have
contributed to hallway air samples being PCR positive..The contamination identified may have accumulated
over the extended periods of occupancy and may represent the high frequency of reported PCR positive sites,
Floor samples were most heavily reported which supports this finding. The numbers don't match up, Ct values
were converted to pseudo TCID50 values based on an equation that obscures what Cts were actually recorded.
Reporting 100% or 200% increases in RNA levels is actually only 2–3 fold, and not the way viruses replicate (i.e.
exponentially).
  •   Neither plaque assay nor serial passage was attempted in the study. The statistical inferences are very difficult
to interpret in Figure 1 when you look at the error bars. The broad sweeping conclusions that SARS-CoV-2 RNA
exists in respired aerosols less than 5 µm in diameter; that aerosols containing SARS-CoV-2 RNA exist in particle
modes that are produced during respiration is difficult to justify based on the findings presented.
  •   In Santarpia 2020 (b) There are “six patients in five rooms in two wards on three separate days in April of 2020”
reported in the text. Table S1 reports are 6 rooms (2 are 7A and 7B and 4 are 5A-D). The abstract reports SARS-
CoV-2 RNA was detected in all six rooms – It is therefore not clear whether there are 6 rooms or 5 – One room
had 2 patients so the total could be 7 not 6 patients
  •   There is no information in the patients and sampling is done 2–24 days post 1st covid test and looks like 4 were
sampled less than 3 days post first covid test but there is no information of symptom onset. No ct values were
provided on the testing of the pts when first done. A Ct of 45 for E gene is not considered a usual standard and
is much higher than what most labs use and accept and a lot of background “noise” as a result
  •   It is likely an equation was used to calculate the concentration of the virus, however, it is more robust to measure
the virus directly than use an equation. EM also does not confirm live virus and does not indicate active viral
replication as the authors suggest – where are the comparisons control EM photomicrographs
Winslow R 2021  •   The authors remark they found no significant differences with the environmental variables.
  •   There was no relationship between days unwell at the time of sampling, or nasopharyngeal Ct values between
those who did and did not have viral RNA in air samples.
  •   Participants in our study were on average in their second week of illness when admitted to the hospital (mean
9-days) and when sampled (mean 12-days).
  •   Plated specimens in the presence of antibiotics and antimycotics and after incubation of 5 days plaques were
subjected to RT-PCR for agent identification. A good, well-reported descriptive study. Very low evidence of
environmental contamination and only one NP specimen showed infectivity.
  •   No evidence that CPAP or any of the other procedures raised the risk of infectiousness. The report shows a
breakdown of Ct by gene and comments on CPE, with confirmatory PCR. Shows correlation between symptoms
and Ct and air samples in the range of 35–40 Ct.
  •   Samples with at least one log increase in copy numbers for the E gene (reduced Ct values relative to the original
samples) after 5–7 days propagation in cells compared with the starting value were considered positive by viral
culture.
Zhou J 2020  •   No indication of any particle size-fractionation techniques were used to determine the size range of droplets and
particle differentiation in air sampling. No information on patients is provided and it is possible they were in the
later stages of illness when no virus could be reliably cultivated.
  •   All surface and air samples from the hospital environment had a Ct value >30, in a range where it is extremely
difficult to cultivate the virus. No attempt was made to ensure the sampler was placed at a specific distance from
the individuals.

Discussion

We identified 128 primary observational studies that showed RT-PCR SARS-CoV-2 RNA can be detected in airborne samples in a variety of settings both indoors and outdoors. Several studies did not detect RNA positivity. Some of the reasons for this may be methodological weaknesses in the study design, the lack of validated methods and/or the location and variable distance of the sampling methods. Control sampling for concomitant bacterial or fungal organisms (which can also produce cytopathic effects on cell monolayers) was not generally done, which would serve as useful controls. In one study which looked for multiple bacteria, fungi, and viruses, including SARS-CoV-2, using qPCR assays, they found much higher burdens of nucleic acids from multiple species of commonly encountered pathogenic and non-pathogenic bacteria (e.g., coagulase negative staphylococci and enterococcus and some Gram-negative bacilli), Candida species and Herpes simplex virus and on all sampling days in comparison to the small quantities of SARS-CoV-2 RNA in their airborne samples15. These findings suggest that the presence of bioaerosolized DNA or RNA from multiple microbes in hospitals is commonplace, and none of these commonly-encountered organisms are considered to be transmitted by the airborne route.

Past attempts to detect infectious particles have proved difficult: aerosols are dilute, and culturing fine particles is problematic. In a NEJM editorial, Roy et al. report ‘the only clear proof that any communicable disease is transmitted by aerosol came from the famous experiment by Wells, Riley, and Mills in the 1950s, which required years of continual exposure of a large colony of guinea pigs to a clinical ward filled with patients who had active tuberculosis16.’ A 2019 review reported that viral RNA or DNA, depending on the virus, could be found in the air near patients with influenza, respiratory syncytial virus, adenovirus, rhinovirus, and other coronaviruses but rarely reported viable viruses17. For coronaviruses including SARS-CoV-1 and MERS-CoV, previous review evidence supporting the airborne route of transmission is weak18; The majority of the studies included in our systematic review and reported in the tables, do not find evidence to support the airborne transmission route. An included US study performed active case finding from two index patients and 421 exposed HCWs [Bays D 2020]. Eight secondary infections in HCWs were reported, but despite multiple aerosol-generating procedures, there was no evidence of airborne transmission. No transmission events were found in multiple high-risk exposures from five symptomatic COVID-19 health care workers with low Ct values [Mponponsuo K 2020]; and Wong SCY et al. reported that none of 120 contacts of a patient with initially undetected COVID-19 subsequently became infectious.

Strengths and limitations

There is a current dearth of well-conducted high-quality studies addressing airborne transmission. To our knowledge, this is the most comprehensive review assessing airborne transmission of SARS-CoV-2. We extensively searched the literature, and we accounted for the reporting quality of the included studies, including the methods used for air sampling and viral culture. However, we recognize several limitations. The findings of our review are limited by the low-quality of the included studies that lack standardised protocols, methods, reporting and outcomes. The small sample sizes, the absence of study protocols and the lack of replication further limit any firm conclusions to be drawn from the findings. Sporadic isolation of viral RNA may be due to problems with sampling techniques. Furthermore, while our search was comprehensive, we may have missed some studies. The lack of standardised reporting means it can be difficult to find essential study details about the methods and the results.

Implications for research

Evidence from the referenced systematic reviews we found noted the need to improve the quality of the primary studies. Anderson et al. reported the need for further data collection under differing temperature and humidity conditions19. Carducci et al. considered no studies had sufficient confirmatory evidence, and airborne transmission remains hypothesis-driven20, Schünemann et al. noted direct studies in COVID-19 are limited and poorly reported21, and Mousavi et al. noted the need for rigorous and feasible lines of research in the area of air filtration and recirculation in healthcare facilities22.

Future studies are warranted to verify findings before definitive conclusions can be reached about modes of transmission and including important knowledge regarding the minimal infectious dose for a specific mode of transmission. Because of the heterogeneity of the settings, the case-mix limitations, the timing between symptom onset and sampling, the sampling techniques used, the lack of clear descriptions and variable study protocols, it is difficult to make meaningful comparisons of air sampling positivity or viral concentrations between settings. Many factors, including relative humidity, temperature, aerosolization medium, exposure period, the chemical composition of the air, seasonality, sampling methods, and ultraviolet light exposure, can affect the potential infectivity of airborne viruses. While sampling techniques have improved greatly over time, the lack of standardisation requires attention as it limits the development of general recommendations for the sampling of airborne viruses23.

One essential question is whether observed epidemiologic associations are causal24,25. Establishing transmission modes requires integrated epidemiological and mechanistic approaches to narrow uncertainty9. Transmission evidence should be context-specific to particular settings (i.e., indoor or outdoor), environment-specific (i.e., the presence of UV light. ventilation etc.) and should ensure that there is evidence of exposure to a transmissible agent. Methodological issues of the culture methods used, as well as knowledge of the infectiousness of the patient, hinder interpretation and suggest that the results should be interpreted with caution. Identifying those circumstances that promote transmission using all relevant evidence that would be more likely to promote viral transmission is important, as well as for identifying interventions. Any study based on epidemiological associations regarding infectious agents should ideally have confirmation from whole genome sequencing. Sequencing has repeatedly shown that outbreaks initially thought to share a single origin were, in fact, the product of multiple independent infection events26.

It is worthy to note that when conducting environmental sampling only a small fraction of the detectable nucleic acids is necessarily incorporated into virus particles, and not all the particles are intact and infectious. It can also take variable numbers of infectious virions to initiate an infection, with this “minimal infectious dose” varying depending upon many factors including the disease agent, route of infection, the host, host age, underlying health conditions, and host immune status. Even a relatively straightforward measurement like particles-to-PFU varies widely among different viruses27. Of special importance is data from a recent human challenge trial28 where an intranasal dose of 10 TCID50 (~7 PFU) virus yielded 53% attack rates. Given that one PFU corresponds to ~160,000 genome copies in human clinical specimens29 one can then estimate that an exposure to >1 million genome copies might be required to yield a ~50% chance of infection. Given the high Ct values detected in the majority of air samples, and the poorly designed and reported virological assays, further research and standardisation of the protocols used to measure genome copies and assay for virus are required in clarifying whether air samples of SARS-CoV-2 are truly infectious.

We found that air samples in the same hospital were more likely to be positive in ICU environments than in the non-ICU. These results are homogenous. However, this observation should be interpreted with caution as the lack of information on the individual demographics of the patients (e.g., symptom onset, underlying illness and degree of immunocompromise) and lack of standardisation across the studies limits the complete interpretation of the result. Detection of SARS-CoV-2 RNA in the air cannot confirm transmission, since only infectious virions can cause disease, but it can be a useful tool for surveillance.

Because of the widespread misunderstanding over the role of PCR positivity in assigning transmission causation, we have proposed a framework for reporting studies that assess causality that helps strengthen the methods used for conducting and reporting respiratory virus transmission research30. The reporting of viral RNA concentrations was heterogeneous as were the sampling methods.

Our proposed framework requires serial viral culture, genome sequencing and evidence that the source was sufficiently contaminated (low Ct) with infectious material (cultivatable virus) to transmit infection to another human. Availability of all such evidence provides a high standard of proof of transmission30.

In some studies, the setting fitted within the definition of transmission in a close contact setting. For example, in Lednicky JA 2021 and Linde KJ 2022, the distances between the index patients and the exposure participants (from which positive cultures were reported) were within 3 feet and 6 feet respectively.

None of the included studies definitively demonstrated that replication-competent SARS-CoV-2 can be recovered in the air, which offers the most robust evidence of transmissibility31. CPE alone cannot be relied upon to establish SARS-CoV-2 replication and additional methods are required, including demonstration of viral growth on permissive cell lines, immunofluorescence staining, and confirming the exclusion of other pathogens or contaminants with sequence confirmation.

General virus-induced CPE were observed in Lednicky JA 20202b however, RT-PCR tests for SARS-CoV-2 were negative while three other respiratory viruses were identified: Influenza A H1N1, Influenza A H3N2, and human coronavirus OC43.32. Similarly, Nannu Shankar S 2021 reported positive culture in 4/16 air samples from a patient’s home. However, the patient was co-infected with HAdV B3, which outgrew SARS-CoV-2 in Vero E6 cells. Both studies demonstrate the importance of testing cultured samples for other viruses.

In further versions of this review, we plan to focus solely on those studies that attempted serial viral culture, given its vital role for establishing transmission causality. This is similar to the methods we used to assess the transmission of Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) from pre and asymptomatic infected individuals14. By reviewing only the high-quality studies we were able to provide probable evidence of SARS-CoV-2 transmission from presymptomatic and asymptomatic individuals. This update required writing to authors to clarify methods and obtain missing information this is beyond the scope of this current update. We have published a protocol outlining the additional methods33.

Conclusion

SARS-COV-2 RNA can be detected by RT-PCR in the air in a variety of settings. The lack of definitive consistently recoverable viral culture samples of SARS-CoV-2 prevents firm conclusions to be drawn about the relative contribution of airborne transmission of this virus. Although airborne transmission of SARS-CoV-2 cannot be ruled out, particularly in certain situational settings, further research is required to investigate the plausibility of such transmission. The current evidence is low quality, and there is a need to standardise methods and improve reporting.

Comments on this article Comments (3)

Version 3
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Version 2
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  • Reader Comment 20 Sep 2021
    Étienne Booth, Université du Québec à Chicoutimi, Saguenay, Canada
    20 Sep 2021
    Reader Comment
    Heneghan et al’s submission of SARS-CoV-2 and the role of airborne transmission: a systematic review in an Open Research publishing platform is commendable. It is in my opinion an encouraging ... Continue reading
  • Discussion is closed on this version, please comment on the latest version above.
Version 1
VERSION 1 PUBLISHED 24 Mar 2021
Discussion is closed on this version, please comment on the latest version above.
  • Reader Comment 19 May 2021
    Raymond Tellier, McGill University, Montreal, Canada
    19 May 2021
    Reader Comment
    Regarding the review in Heneghan et al. of Lednicky 2020a [1], which reported successful isolation in cell culture of SARS-CoV-2 from aerosol samples: Heneghan et al. take issues with the ... Continue reading
  • Reader Comment 14 May 2021
    Jose-Luis Jimenez, University of Colorado-Boulder, USA
    14 May 2021
    Reader Comment
    Heneghan et al’s paper is not, as it claims, a systematic review on the role of airborne transmission for SARS-CoV-2 (Heneghan et al. 2021). The mismatch between the paper’s title, ... Continue reading
  • Discussion is closed on this version, please comment on the latest version above.
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Heneghan CJ, Spencer EA, Brassey J et al. SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.12688/f1000research.52091.3)
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
Version 3
VERSION 3
PUBLISHED 19 Oct 2022
Revised
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Reviewer Report 25 May 2023
Jennifer Grant, Faculty of Medicine, The University of British Columbia, Vancouver, British Columbia, Canada 
Approved
VIEWS 50
Thank you for this interesting study. A couple of comments:
  1. It would be nice to know in which way you modified the QUADAS 2 tool if it is possible to put that in an annex or
... Continue reading
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Grant J. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.139143.r172710)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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PUBLISHED 06 Sep 2021
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Reviewer Report 05 Oct 2021
Maosheng Yao, College of Environmental Sciences and Engineering, Peking University, Beijing, China 
Not Approved
VIEWS 86
I just read their responses to my comments. First, a thank you to the authors for taking their valuable time to respond. Unfortunately, I found none of my critiques have been adequately answered. Thus, I feel that I do not ... Continue reading
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Yao M. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.77065.r93516)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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171
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Reviewer Report 16 Sep 2021
David R. Tomlinson, University Hospitals Plymouth NHS Trust, Plymouth, UK 
Not Approved
VIEWS 171
Dear Professor Heneghan and team,

Thank you for responding to my submitted comments following my review of version 1 ‘SARS-CoV-2 and the role of airborne transmission: a systematic review’. I hope that my responses herein to your ... Continue reading
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HOW TO CITE THIS REPORT
Tomlinson DR. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.77065.r93514)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
Version 1
VERSION 1
PUBLISHED 24 Mar 2021
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217
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Reviewer Report 05 May 2021
Maosheng Yao, College of Environmental Sciences and Engineering, Peking University, Beijing, China 
Not Approved
VIEWS 217
Review for Heneghan et al. (2021), SARS-CoV-2 and the role of airborne transmission: a systematic review, F1000Research 2021, 10:232 .

First, I have to declare that this review is provided solely based on scientific evidence and reasoning without ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Yao M. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.55319.r82052)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, Oxford, UK
    06 Sep 2021
    Author Response
    Peer Reviewer #3

    First, I have to declare that this review is provided solely based on scientific evidence and reasoning without any discipline preferences or conflicting interests. Despite not ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, Oxford, UK
    06 Sep 2021
    Author Response
    Peer Reviewer #3

    First, I have to declare that this review is provided solely based on scientific evidence and reasoning without any discipline preferences or conflicting interests. Despite not ... Continue reading
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331
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Reviewer Report 22 Apr 2021
Nancy H. L. Leung, WHO Collaborating Centre for Infectious Disease Epidemiology and Control, School of Public Health, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong, Hong Kong 
Approved with Reservations
VIEWS 331
In this systematic review, Heneghan et al. attempted to summarise the literature on the role of airborne transmission for SARS-CoV-2, with a focus of air sampling studies or epidemiologic studies that may evaluate the aerosol mode of transmission. They described ... Continue reading
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HOW TO CITE THIS REPORT
Leung NHL. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.55319.r82064)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, UK
    06 Sep 2021
    Author Response
    Peer reviewer 2

    1. In this systematic review, Heneghan et al. attempted to summarise the literature on the role of airborne transmission for SARS-CoV-2, with a focus of air sampling studies ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, UK
    06 Sep 2021
    Author Response
    Peer reviewer 2

    1. In this systematic review, Heneghan et al. attempted to summarise the literature on the role of airborne transmission for SARS-CoV-2, with a focus of air sampling studies ... Continue reading
Views
1201
Cite
Reviewer Report 16 Apr 2021
David R. Tomlinson, University Hospitals Plymouth NHS Trust, Plymouth, UK 
Not Approved
VIEWS 1201
Dear Professor Heneghan and team,

I would firstly like to congratulate you for publishing this systematic review on an open access site and for inviting comments. I am grateful for being given the opportunity to respond and ... Continue reading
CITE
CITE
HOW TO CITE THIS REPORT
Tomlinson DR. Reviewer Report For: SARS-CoV-2 and the role of airborne transmission: a systematic review [version 3; peer review: 1 approved, 1 approved with reservations, 2 not approved]. F1000Research 2022, 10:232 (https://doi.org/10.5256/f1000research.55319.r82591)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, UK
    06 Sep 2021
    Author Response
    Peer reviewers’ comments
    Authors’ responses

    Peer Reviewer #1

    Dear Professor Heneghan and team,

    I would firstly like to congratulate you for publishing this systematic review on an ... Continue reading
COMMENTS ON THIS REPORT
  • Author Response 06 Sep 2021
    Carl Carl, University of Oxford, UK
    06 Sep 2021
    Author Response
    Peer reviewers’ comments
    Authors’ responses

    Peer Reviewer #1

    Dear Professor Heneghan and team,

    I would firstly like to congratulate you for publishing this systematic review on an ... Continue reading

Comments on this article Comments (3)

Version 3
VERSION 3 PUBLISHED 19 Oct 2022
Revised
Version 2
VERSION 2 PUBLISHED 06 Sep 2021
Revised
Discussion is closed on this version, please comment on the latest version above.
  • Reader Comment 20 Sep 2021
    Étienne Booth, Université du Québec à Chicoutimi, Saguenay, Canada
    20 Sep 2021
    Reader Comment
    Heneghan et al’s submission of SARS-CoV-2 and the role of airborne transmission: a systematic review in an Open Research publishing platform is commendable. It is in my opinion an encouraging ... Continue reading
  • Discussion is closed on this version, please comment on the latest version above.
Version 1
VERSION 1 PUBLISHED 24 Mar 2021
Discussion is closed on this version, please comment on the latest version above.
  • Reader Comment 19 May 2021
    Raymond Tellier, McGill University, Montreal, Canada
    19 May 2021
    Reader Comment
    Regarding the review in Heneghan et al. of Lednicky 2020a [1], which reported successful isolation in cell culture of SARS-CoV-2 from aerosol samples: Heneghan et al. take issues with the ... Continue reading
  • Reader Comment 14 May 2021
    Jose-Luis Jimenez, University of Colorado-Boulder, USA
    14 May 2021
    Reader Comment
    Heneghan et al’s paper is not, as it claims, a systematic review on the role of airborne transmission for SARS-CoV-2 (Heneghan et al. 2021). The mismatch between the paper’s title, ... Continue reading
  • Discussion is closed on this version, please comment on the latest version above.
Alongside their report, reviewers assign a status to the article:
Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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