Background: The positive associations between ambient PM2.5 and cardiorespiratory disease have been well demonstrated during the past decade. However, few studies have examined the adverse effects of PM2.5 based on an entire population of megalopolis. In addition, due to the lack of accurate methods of assessing individual PM2.5 exposure, further studies are still necessary to be launched in China.Methods: The study was conducted in Wuhan, a megacity in central China with about 10.8929 million

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... opulation. Daily hospital admission records, from October 2016 to December 2018, were obtained from Wuhan Information center of Health and Family Planning, which administrates all the hospitals in Wuhan. The daily air pollution concentration and weather variable in Wuhan during the study period were collected. We developed Land use regression model (LUR) to assess individual PM2.5 exposure. Time-stratified case-crossover design and conditional logistic regression models were adopted to estimate cardiorespiratory hospitalization risks associated with short-term exposures to PM2.5. We also conducted stratification analyses by age, sex and season.Results: A total of 2,806,115 hospital admissions records were collected during the study period, from which we identified 332,090 for total cardiovascular diseases and 159,365 for total respiratory diseases. We found short-term PM2.5 exposure was associated with increased risk of cardiorespiratory hospital admission in Wuhan. Per 10 μg/m3 increase of PM2.5 at lag0~2 days was associated with 1.23% (95%CI: 1.01–1.45%) and 1.95% (95%CI: 1.63–2.27%) elevated risk of admission from cardiovascular and respiratory diseases respectively. The elderly were at higher PM-induced risks. The associations appeared to be more evident in the cold season than in the warm season.Conclusions: This study contributed evidence to support the short-term effects of PM2.5 on cardiorespiratory hospital admission, which may be helpful for air pollution control and disease prevention in Wuhan.