The burden of acute conjunctivitis attributable to ambient particulate matter pollution in Singapore and its exacerbation during South-East Asian haze episodes

Abstract

Introduction: Urban air quality in South-East Asia is influenced by local and transboundary sources of air pollutants. Research studies have well characterized the short-term effects of air pollution on cardiovascular and respiratory health but less so on ocular health. We investigated the relationship between air pollution and acute conjunctivitis in Singapore, a tropical city-state located in South-East Asia.

Methods: Assuming a negative-binomial distribution, we examined the short-term associations between all-cause acute conjunctivitis reports from 2009 to 2018 and contemporaneous ambient air pollutant concentrations using a time-series analysis. In separate pollutant models for PM_2.5 and PM₁₀, we fitted fractional polynomials to investigate the linearity between air pollutant exposures and conjunctivitis, adjusting for long-term trend, seasonality, climate variability, public holidays, immediate and lagged exposure effects, and autocorrelation.

Results: There were 261,959 acute conjunctivitis reports over the study period. Every 10 μg/m³ increase in PM_2.5 was associated with a 3.8% (Incidence Rate Ratio (IRR): 1.038, 95% Confidence Interval (CI): 1.029-1.046, p < 0.001) cumulative increase in risk of conjunctivitis over the present and subsequent week. Every 10 μg/m³ increase in PM₁₀ was associated with a 2.9% (Incidence Rate Ratio (IRR): 1.029, 95% Confidence Interval (CI): 1.022-1.036, p < 0.001) cumulative increase in risk of conjunctivitis over the present and subsequent week. Acute conjunctivitis reports exhibited an inverse dependence on ambient air temperature and relative humidity variability. Approximately 3% of all acute conjunctivitis reports were attributable to PM_2.5. Particulate matter attributed acute conjunctivitis was disproportionately higher during transboundary haze episodes.

Conclusion: Our study strengthens the evidence linking particulate matter exposure to an increased risk of conjunctival disease, with a disproportionately higher disease burden during South-East Asia transboundary haze episodes. Our findings underscore the importance of reducing the health impact of indigenous and transboundary sources of ambient particulate matter pollution.

Keywords: Air pollution; Conjunctivitis; Particulate matter; Singapore; Time-series.