Quantifying the associations of the air pollutant SO2 on outpatient visits for conjunctivitis in Hangzhou, China

The aim of this study is to further investigate the single and cumulative associations of SO2 on outpatient visits for conjunctivitis. Data from outpatient visits, air pollutants, and meteorology was collected by the Eye Center of the Second Affiliated Hospital of the Zhejiang University School of Medicine, the Environmental Protection Department of Zhejiang Province, and the Meteorological Administration of Zhejiang Province from July 1, 2014, to November 30, 2019. A Poisson generalized linear regression model (PGLM), combined with a distributed lag nonlinear model (DLNM), was employed to analyze the association between SO2 and outpatient visits for conjunctivitis using PM2.5 and NO2 as covariates. Of the 539,649 outpatients for conjunctivitis recruited for analysis, 58.1% were female. Obvious single associations of SO2 were observed in outpatient visits for conjunctivitis, which is consistent with our previous results using a time-stratified case crossover design. A delay in the associations of -SO2 on outpatient visits for conjunctivitis was further confirmed, with the longest lag being 12 days. The strongest lag effect was found at lag 0-11 with RR95th vs (25th) = 1.30 (1.24, 1.37), and RR90h vs (25th) = 1.23 (1.18, 1.28). Furthermore, the results showed that old people may be more sensitive to the associations of SO2 than adults and the younger ones. Our study provides the first evidence that outpatient visits for conjunctivitis are positively associated with both single and cumulative air pollutant SO2 exposure, suggesting that people especially elders had better to decrease outdoor activities when the SO2 concentration is above safe level.