Intraday Exposure to Ambient Ozone and Emergency Department Visits among Children: a Case-Crossover Study in Southern China.

Most existing studies have investigated short-term associations between ozone exposure and acute disease events among children at a daily timescale, which might neglect risk effects happening within several hours after ozone exposure. In this research, we aimed to depict intraday associations between pediatric emergency department visits (PEDVs) and exposure to ozone in order to better detect ultra-short-term effects of ozone exposure on children. We obtained hourly data of all-cause PEDVs, air pollutants, and meteorological factors in Shenzhen and Guangzhou, China, 2015–2018. We applied time-stratified case-crossover design and conditional logistic regression models to estimate odds ratios per 10-μg/m3 rise of ozone concentrations at various exposure periods (e.g., 0–3, 4–6, 7–12, 13–24, 25–48, and 49–72 h) prior to PEDVs, controlling for hourly relative humidity and temperature. Subgroup analyses divided by gender, age, and season were undertaken to identify the potential susceptible population and period. A total of 358,285 cases of PEDVs were included in two cities, and hourly average concentration of ozone was 45.5 μg/m3 in Guangzhou and 58.9 μg/m3 in Shenzhen, respectively. Increased risks of PEDVs occurred within a few hours (0–3 h) after exposure to ozone and remained up to 48 h. Population risks for PEDVs increased by 0.8