Daily gaseous air pollution and pediatric conjunctivitis: A case-crossover study across ten cities in China's southeastern coastal region.

The evidence on associations between ambient gaseous pollutants and conjunctivitis remains inconclusive, and limited research is available, particularly regarding children. Based on a case-crossover study conducted in ten Chinese cities from 2013 to 2023, we documented 418,027 outpatient visits for conjunctivitis in children. Of these visits, 256,525 were for boys and 161,502 for girls. A one standard deviation (SD) increase in daily concentrations of carbon monoxide (CO) was related to a 1.20 % rise in same-day outpatient visits for pediatric conjunctivitis (OR = 1.012, 95 % CI: 1.005, 1.018). Similar associations were found for nitrogen dioxide (NO2: 2.90 % increase; OR = 1.029, 95 % CI: 1.019, 1.040), sulfur dioxide (SO2: 1.70 % increase; OR = 1.017, 95 % CI: 1.007, 1.028), and ozone (O3: 1.30 % increase; OR = 1.013, 95 % CI: 1.006, 1.021). The positive associations remained significant in two-pollutant and mixed-effects models. Notably, we observed stronger associations in girls compared to boys, among children at 1-5 years of age compared to other age groups, and the relationships were more pronounced during the summer months. This study reveals a link between exposure to common gaseous air pollutants and increased risks of conjunctivitis in children, indicating the potential benefits of public health interventions.