Prevalence of organophosphate poisoning in Nepal: A Meta-Analysis

Strengths and limitations of this study

1. Introduction

Organophosphate (OP) [broader term organophosphorus] poisoning predominantly occurs in agriculture-based countries, where these substances are easily accessible. Exposure to OP can result from occupational or accidental contact with pesticides, intentional self-harm, or chemical warfare and terrorist attacks.^1,2 OP is responsible for approximately two-thirds of the estimated 60% of pesticide poisoning-related deaths from self-harm that occur annually in rural Asia.³ Suicide remains a serious public health issue, affecting approximately 79% of cases occurring in low- and middle-income nations, frequently due to pesticide self-poisoning.^4,5 The fatality rate of OP poisoning is as high as 25%, surpassing that of other types of poisoning.⁶

OP poisoning is commonly observed in Nepal, China,⁷ Taiwan,⁸ India,⁹ Bangladesh,¹⁰ and other parts of the world.⁴ In this study, data from 108 countries illustrated that pesticide self-poisoning deaths comprised 13.7% of all global suicides.⁴ Pesticides are widely accessible in Nepal, which is located in South Asia where most Nepalese work in agriculture and farming, making them the most common cause of poisoning. Commonly used OP compounds in Nepal include malathion, metacids, dichlorphos, cypermethrin, defox, and chlorpyriphos.¹¹ However, the Nepalese government does not have exact data regarding the prevalence of OP poisoning. The absence of strict market inspections and widespread availability of OP have further exacerbated their misuse in agriculturally dominant areas.

This study aimed to explore the prevalence of OP poisoning in Nepal by including all relevant articles available in major databases such as PubMed, Web of Science Core Collection (WoSCC), Cochrane Library, Ovid, and Springer. By analyzing a broader range of research data, we seek to provide stronger evidence on this critical public health issue in Nepal.

2. Methods

3. Results

3.1 Study retrieval results

Through an extensive review and strict compliance with the inclusion criteria, 11 articles met the inclusion criteria and were included in this study ( Figure 1). A total of 4809 participants were included. Basic information for each study is presented in Table 2 (refer to extended data). All included studies were published between 2016 and 2024 on the Nepalese population from different places in Nepal.

Figure 1. Flow diagram of literature screening.

Organophosphate (OP) poisoning in Nepal.

3.2 Results of meta analysis

Table 3 (refer to extended data) shows the results of quality assessment of the included studies. It was found that Subedi et al.¹¹ had a low risk of bias; however, other studies had a moderate risk of bias according to the JBI appraisal checklist.

The heterogeneity test showed that the P value was <0.100. As a result, we chose the pooled prevalence rate from the results of the random effects model. The overall prevalence of OP poisoning was 36.7% (95% CI: 24.99-49.34) in Nepal ( Figure 2).

Figure 2. Meta-analysis forest plot of the prevalence OP poisoning.

Using random effects model (I²=99.3%) 36.7% (95% CI: 24.99-49.34). CI, confidence interval.

In the sensitivity analysis, we divided the studies into hospital- and community-based studies. It was found that pooled prevalence rate of hospital-based studies was 36.9% (95% CI: 24.2-50.6), and that of the community-based studies was 35.22% (95% CI: 2.8-79.1) (Table 4 refer to extended data).

In the sensitivity analysis, we divided studies into Other cities-based and Kathmandu-based studies. It was found that pooled prevalence rate of Other cities-based studies was 43.38% (95% CI: 28.95-58.39) and pooled prevalence rate of Kathmandu-based studies was 35.41% (95% CI: 19.5-53.2) (Table 4 refer to extended data).

3.3 Assessment of publication bias

A funnel plot was used to evaluate publication bias of the included studies. The funnel plot was asymmetric on both sides ( Figure 3), indicating that publication bias should not be ignored.

Figure 3. Funnel plot of the relationship of 11 articles.

4. Discussion

To the best of our knowledge, this is the first meta-analysis to report on the prevalence of OP poisoning in Nepal. Our findings revealed that the overall prevalence of OP poisoning in Nepal is 36.7%. The prevalence of OP poisoning varies significantly worldwide, with rates reported at 3% in Serbia,¹³ 26.9% in China,⁷ and 4.6% in India.⁶ This implies that the prevalence of OP poisoning in Nepal may be substantially higher than in other regions. Our meta-analysis also highlighted sex differences in OP poisoning cases. Most studies showed a higher female-to-male ratio, such as 2.9:1 by Subedi et al.,¹¹ 1.4:1 by Basnet et al.,³ 1.5:1 by Pandey et al.,¹⁴ 2.1:1 by Bhusal et al.,¹⁵ and 1.9:1 by Aryal et al.¹⁶ In contrast, Khan et al.¹⁷ reported a higher male-to-female ratio (0.8:1). Similarly, a study conducted in China from to 2012-2016 involving 5009 patients reported a higher female ratio (1.2:1), with 56.7% of cases arising from suicide attempts.⁷

Significant heterogeneity was observed among the included studies, prompting subgroup analyses of hospital and community-based studies to determine the potential sources of heterogeneity. From the data of the included individual studies, it was found that the prevalence rates were higher in hospital-based studies than in community-based studies, which may be partly attributed to the fact that patients in hospital settings are more likely to undergo relevant diagnostic evaluations than those in community settings. In this meta-analysis, all authors of the included papers researched the Nepalese population and determined its prevalence. The authors of the included papers conducted research across various districts of Nepal with a primary focus on Kathmandu, ensuring that the analysis was not confined to a single district or region. Most studies were conducted in Kathmandu, where a large population resides. However, in this meta-analysis we found that Other cities-based studies shows more prevalence of OP poisoning than Kathmandu based, potentially due to larger sample size in the published papers from other cities. In terms of study design, Dea Haagensen Kofod¹⁸ performed community-based tests and Rakesh Ghimire⁵ performed both hospital- and community-based tests. However, the remaining studies were hospital-based.^{3,11,14,15,17,19–21}

Our study has several limitations. First, only 11 studies were retrieved from the major literature databases. Second, significant heterogeneity and publication bias were observed, likely due to the bias of small-sample studies and study sites with different OP poisoning prevalence rates. Third, limited data were available from certain districts of Nepal, which prevented a complete understanding of national prevalence. To address these gaps, future research should include high-quality cohort and case-control studies from a broader geographical range within Nepal.

5. Conclusions

Our study provides valuable insights into the prevalence of OP poisoning in Nepal, with an overall rate of 36.7%. Hospital-based studies have reported a higher pooled prevalence rate than community-based studies, and studies conducted in other cities have shown a higher prevalence than those conducted within Kathmandu. More studies, particularly those from underrepresented regions, are necessary to obtain more accurate and comprehensive data on OP poisoning in Nepal.

Author contributions

Nitesh Shrestha designed the framework of the manuscript, performed the meta-analysis, and drafted and revised the manuscript. Tao Wei performed the meta-analysis and revised the manuscript accordingly. Rui Liao drafted and revised the manuscript accordingly. Qiang Xue, Jia Hu, Xia Zhao, and Qin Huang searched for relevant literature, and reviewed and revised the manuscript accordingly.

Ethics and consent

Ethical approval and consent were not required.