Abstract
BACKGROUND: Children's respiratory health demonstrates particular sensitivity to air pollution. Existing evidence investigating the association between short-term ozone (O(3)) exposure and childhood pneumonia remains insufficient and inconsistent, especially in low- and middle-income countries (LMICs). METHOD: To provide more reliable and persuasive evidence, we implemented a multi-city, time-stratified case-crossover design with a large sample size, using data from seven representative children's hospitals across major geographical regions in China. To avoid the impact of the COVID-19 pandemic, individual-level medical records of inpatient children under 6 years of age diagnosed with pneumonia during 2016-2019 were collected. Conditional logistic regression models were fitted for each city, and city-specific estimates were pooled through a meta-analysis using a random-effects model. RESULTS: In total, the study included 137,470 pediatric pneumonia hospital admissions. The highest pooled estimate for O(3) occurred at lag0-1, with a 10 µg/m(3) increase in O(3) associated with a 1.57% (95% CI: 0.67%-2.48%) higher risk of pediatric pneumonia hospital admissions. Stratified analyses indicated that the effects of O(3) were robust across different sexes, age groups, and admission seasons. We also observed a statistically significant increase in risk associated with O(3) concentrations exceeding the World Health Organization Air Quality Guidelines (WHO-AQGs). CONCLUSIONS: This study revealed a significant positive association between O(3) and pediatric pneumonia hospital admissions. Our findings substantially strengthen the evidence base for the adverse health impacts of O(3), underscoring the importance of O(3) pollution control and management in reducing the public health burden of pediatric pneumonia.