Attributable risks of emergency hospital visits due to air pollutants in China: A multi-city study.

Air pollution is associated with risks of mortality in China, but the evidence is still limited for morbidity. This study aims to examine overall effects of ambient air pollutants on emergency hospital visits (EHVs) at the national level in China and calculate corresponding attributable risks. We collected daily data for EHVs from 33 largest hospitals in China between Oct 2013 and Dec 2014, as well as daily measurements of particulate matter (PM10 and PM2.5: particles with aerodynamic diameter < 10 μm and 2.5 μm, respectively), nitrogen dioxide (NO2) and sulphur dioxide (SO2) from 31 cities where the hospitals were located. Firstly, quasi-Poisson regression with a constrained distributed lag model (CDLM) was employed to examine city-specific associations of EHVs with each pollutant. Then, the effects at the national scale were pooled with a random-effect meta-analysis. Daily EHVs was significantly associated with a 10 μg/m3 increase in PM2.5 at lag 0-2 days [cumulative relative risk (RR) and 95% confidence intervals (CI): 1.006 (1.002, 1.009)], PM10 at lag 0-1 days [1.004 (1.002, 1.006)], NO2 at lag 0-1 days [1.015 (1.010, 1.019)] and SO2 at lag 0-2 days [1.022 (1.014, 1.030)]. The effect estimates were not modified by sex, but stronger effects were observed among children than adults. Overall, 3.34% of EHVs may result from exposure to ambient PM2.5, 3.96% to PM10, 5.90% to NO2 and 5.38% to SO2. Exposure to outdoor air pollution has acute effects on EHVs. Effective measures to control air pollution levels in China could potentially reduce demands for emergency hospital services.