Quantifying the associations of the air pollutant SO 2 on outpatient visits for conjunctivitis in Hangzhou, China

The aim of this study is to further investigate the single and cumulative associations of SO 2 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 SO 2 and outpatient visits for conjunctivitis using PM 2.5 and NO 2 as covariates. Of the 539,649 outpatients for conjunctivitis recruited for analysis, 58.1% were female. Obvious single associations of SO 2 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 SO 2 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 RR 95th vs 25th = 1.30 (1.24, 1.37), and RR 90h vs 25th = 1.23 (1.18, 1.28). Furthermore, the results showed that old people may be more sensitive to the associations of SO 2 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 SO 2 exposure, suggesting that people especially elders had better to decrease outdoor activities when the SO 2 concentration is above safe level.