Weather, Air Pollution, and Seasonality: Predictors of Pathogen-Associated Conjunctivitis Outbreaks in Kathmandu Valley, Nepal.

Conjunctivitis outbreaks can herald pandemics. However, their relationships with weather and air pollution factors are not well understood. Kathmandu in Nepal has defined wet-dry seasons and lies in a bowl-shaped valley that traps air pollutants with levels many-folds higher than recommended by World Health Organization (WHO). From 2021 to 2023, we collected conjunctival samples from patients with presumed infectious conjunctivitis in Kathmandu, Nepal, for pathogen identification. With publicly available weather and air quality databases, we assessed the relationship between environmental factors and the prevalence of different pathogen types by performing binary logistic regression model building and cosinor regression analysis. High precipitation was associated with an increased odds of RNA virus infection (odds ratio [OR] = 1.82; 95% CI = 1.24-2.72; P = 0.003), whereas higher ozone levels were associated with decreased odds of RNA virus infections (OR = 0.46; 95% CI = 0.29-0.69; P <0.001). The odds of bacterial infection increased 4.2-fold for every 1 SD µg/m3 increase in ozone (SD = 11 µg/m3; 95% CI = 1.75-11.67; P <0.001), and the odds of fungal infection increased 1.62-fold for every 1 SD µg/m3 increase in nitric oxide (SD = 0.97 µg/m3; 95% CI = 1.02-2.49; P = 0.041). Cases associated with different taxa peaked at different times: pre-monsoon season for bacteria, during monsoon season for RNA viruses, and post-monsoon season for fungi. Our results suggest the importance and varying influence of local climate and air quality conditions on the etiology of conjunctivitis.