Ambient Particulate Matter Concentrations and Hospital Admissions in 26 of China's Largest Cities: A Case-Crossover Study

Background: Few studies have evaluated the short-term impacts of ambient particulate matter (PM) pollution on morbidity in China. The aims of this study were to examine the short-term association between hospital admissions and ambient PM and also to explore whether PM2.5 at levels below current regulatory limits also increases the risk of hospitalizations in 26 Chinese cities. Methods: We identified 14,569,622 all-cause, 2,008,786 cardiovascular, and 916,388 respiratory admissions during 2014-2015. We employed conditional logistic regression to estimate the association between hospital admissions and ambient PM. Results: A 10 g/m(3) increase in PM2.5 at lag 0 day corresponded to increases of 0.19% (95% confidence interval [CI] = 0.18%, 0.20%) in all-cause, 0.23% (95% CI = 0.20%, 0.26%) in cardiovascular, and 0.26% (95% CI = 0.22%, 0.31%) in respiratory admissions. For PM10, the values were 0.12% (95% CI = 0.11%, 0.13%) for all-cause, 0.15% (95% CI = 0.13%, 0.17%) for cardiovascular, and 0.21% (95% CI = 0.17%, 0.24%) for respiratory admissions. The associations held at PM2.5 levels below the current Chinese and European/WHO standards. Among individuals with exposure levels below 25 g/m(3), increasing PM2.5 levels from below 15 g/m(3) to above 15 g/m(3) was associated with increases of 1.8% (odds ratio, 1.018; 95% CI = 1.015, 1.022) in all-cause admissions and 2.5% (odds ratio, 1.025; 95% CI = 1.017, 1.034) in cardiovascular admissions. Conclusions: Short-term PM exposures were associated with increased hospitalizations, even for exposure levels not exceeding the current regulatory limits.