The effect of ambient fine particulate matter (PM2.5) on respiratory diseases in China: a systematic review and meta-analysis

Only a few recent systematic reviews and meta-analysis studies have quantitatively assessed the effect of short-term exposure to ambient fine particular matter with an aerodynamic diameter of less than 2.5 μm (PM2.5) on respiratory disease (RD) mortality and RD hospital outpatient visits in the Chinese population. A total of 46 articles were selected from Web of Science, PubMed, China National Knowledge Infrastructure and Wanfang databases. Generic inverse variance method was employed to pool individual effect estimates. Pooled estimates represented the increased risk of daily RD mortality and RD outpatient visits per 10 µg/m3 increase in PM2.5 concentrations. Positive associations were identified between short-term PM2.5 exposure and RD in China. The risk of RD mortality and RD outpatient visits increased by 0.48% (95% CI 0.40%, 0.55%) and 0.90% (95% CI 0.62%, 1.18%), respectively, per 10 µg/m3 increase in PM2.5 concentrations. A low increased risk of RD outpatient visits (0.62%, 95% CI 0.57%, 0.66%) was identified at a high level of annual mean PM2.5 concentrations (41.36–110.80 µg/m3) with 1.82% (95% CI 1.72%, 1.92%) at a low level of annual mean PM2.5 concentrations (29.86–40.20 µg/m3) through subgroup analysis. Short-term exposure to PM2.5 was associated with increased risks of RD mortality and RD outpatient visits. The increased risk of RD outpatient visits was pronounced at a low level of annual mean PM2.5 concentrations, but the exact mechanisms of this phenomenon require further investigation. Evidence demonstrated in this study could appeal to Chinese policymakers to improve air quality and alleviate the adverse health impact of PM2.5 pollutions.