Effect of elevated temperature on SARS-CoV-2 viability

Introduction

Coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has inflicted disruptions in many aspects of health systems globally. SARS-CoV-2 is an enveloped, non-segmented, positive sense, single-stranded RNA virus with a genome of approximately 30 kilobases.^1,2 The virus is mainly transmitted by nasopharyngeal droplets of an infected person; however, it could also be transmitted through aerosol.³ The viability of the virus in the environment is influenced by several factors, including climatic parameters such as humidity and temperature.⁴ Temperature has been proposed as a factor that affects SARS-CoV-2 transmission.⁵ Previous studies found that the temperature effected the transmission of the SARS-CoV-2 in which high environmental temperature reduced the number of COVID-19 cases.^6–8 A study in State of Rio de Janeiro, Brazil found that the maximum and average of temperature were correlated negatively with COVID-19 infection.⁶ Data from 117 countries also found a negative association between temperature and COVID-19 transmissibility in which an increase of 1°C could decrease COVID-19 prevalence by approximately 5.4%.⁷ Several other investigations, however, have shown no evidence of a substantial influence of temperature on SARS-CoV-2 transmission.^9,10

Nevertheless data reveals that SARS-CoV-2 is highly susceptible to heat.¹¹ A recent study has shown that the virus could survive for at least 14 days at 4°C while only two days at 37°C and five minutes at 70°C.¹¹ Another study suggested that, at 40°C SARS-CoV-2-infected epithelial cells have reduced viral transcription and replication.¹² Although studies on the effect of elevated temperature on SARS-CoV-2 have been carried out, the temperature ranges used are limited.¹³ In addition, the effect of temperature on viruses originating from Indonesia has not yet been published. As part of our project to optimize the isolation chamber for COVID-19 patients, we determined the effect of temperature on the resistance of SARS-CoV-2 originating from Indonesia by evaluating the viral viability with a range of temperatures from room temperature (21-23°C) to 65°C. Understanding viral survivability is critical for developing a temperature optimized isolation chamber that could minimize the risk of infection to healthcare workers and optimize energy consumption while ensuring comfort for patients. In addition, the information of this study might important for those who are living in the tropics.

Methods

Results

The virus was observed to remain stable from RT to 35°C with an average plaque count of 10¹³ PFU/mL.²³ A reduction in the viral count was observed in the 40°C treatment group at 10⁹ PFU/mL. Increasing the temperature to 45°C resulted in a further reduction of the viral viability resulting in 10⁶ PFU/mL. The last temperature with visible plaque was in the 50°C treatment group with a result of 10² PFU/mL. The reduction of SARS-CoV-2 viability had a temperature-dependent trend within the temperature range of 35 to 50°C (Figure 1). No plaques were visible in the 55, 60 and 65°C treatment groups.

Figure 1. The effect of temperature on severe acute respiratory syndrome coronavirus 2 viability.

RT – (21-23°C).

Discussion

Nosocomial transmission of SARS-CoV-2 has been identified to occur via multiple routes in healthcare facilities¹⁴ indicating that uncomplicated measures like wearing personal protective equipment along with surface cleaning and decontamination¹⁵ could be used effectively to reduce the transmission of infection. Other than that, modification to facilities such as, including isolation chambers with temperature control could help minimize the transmission.^11,16 As noted in a previous study,¹¹ temperature affects the stability of the virus in aerosol or on a surface. When the temperature of the room is not elevated, SARS-CoV-2 could remain stable for up to 72 hours on a surface such as plastic and stainless steel and three hours in aerosols.¹⁶ Based on the findings of this present study, to reduce the viral viability significantly, a higher room temperature might be important. However, according to a previous report, the average maximum temperature for Indonesian people to still feel comfortable falls between 24 and 29°C¹⁷ and to increase the room temperature would probably cause discomfort to the patient.

The administration of heat to the isolation chamber could be conducted prior to patient handling to reduce the likelihood of SARS-CoV-2 transmission. The other possibility is using heat in the isolation chamber as a means of thermotherapy. Thermotherapy is where mild-temperature elevation or hyperthermia (39-42°C) is used as a treatment against SARS-CoV-2 infection.¹⁸ Previous studies assessing the indoor temperature and SARS-CoV-2 were associated inactivation of SARS-CoV-2.^19–21 Following the increase in temperature, heat-shock proteins (HSPs) are released which downregulates the progression of sepsis-induced acute lung injury.²² However, HSPs could become hosts to several viruses (such as human papillomavirus, adenovirus, and dengue virus) promoting their infectivity.²³ In the case of SARS-CoV-2, its infectivity is more likely to be degraded than promoted by the HSPs.¹⁸ Therefore, heat administration to the isolation chamber should not be performed on COVID-19 patients with human papillomavirus, adenovirus, or dengue virus co-infections. In addition, it should not be attempted on patients with severe-to-critical COVID-19 as they would be more likely to have an increased risk of mortality following the thermotherapy or heat administration.²⁴

One of the limitations of this study was we did not assess the role of other factors that might influence the SARS-CoV-2 transmission such as humidity. Therefore, the results of our study should be incorporated with data of the other studies assessing the effects of humidity on SARS-CoV-2 viability. In addition, we assessed the effect of the temperature on SARS-CoV-2 in a liquid state only and this might have influenced the results. Assessing the effect of the temperature on different states might could provide better understanding.

Conclusions

This present study also has proven that increasing indoor temperature to 55°C is sufficient to terminate the virus. Further increment to the temperature would not be necessary and only results in higher energy consumption. Similarly, a previous study also reported the inactivation of 90% of SARS-CoV-2 achieved at 54.5°C after 36 minutes.¹³ However, for use in treatment 55°C, might be too high for patients to tolerate. In that case, we only suggest the use of such temperature to thermally sterilize the isolation chamber prior to its use.

Data availability

Ethics statement

Not applicable.