Ambient Particulate Matter Concentrations and Hospitalization for Stroke in 26 Chinese Cities

Background and Purpose— Little is known about the short-term health impacts of particulate matter (PM) on stroke in China. We, therefore, conducted a time-stratified case-crossover study to examine the association between ambient PM and hospital admissions for stroke in 26 Chinese cities. Methods— We identified hospital admissions for stroke by using electronic hospitalization summary reports from January 1, 2014 through December, 31 2015. We applied conditional logistic regression to explore the association between PM and hospital admissions for stroke. We also assessed the effect modification of stroke risk by geographical region, sex, and age. Results— Hospital admissions for ischemic (n=278 980) and hemorrhagic (69 399) strokes were examined separately. For ischemic stroke, both PM 2.5 and PM 10 had the strongest effect at lag 3 days, with an interquartile range increase in PM 2.5 (47.5 μg/m 3 ) and PM 10 (76.9 μg/m 3 ) significantly associated with a 1.0% (95% confidence interval, 0.7%–1.4%) and 0.8% (95% confidence interval, 0.3%–1.3%) increase in admissions for ischemic stroke, respectively. In northern China where PM pollution is more severe, the risk estimates for both PM 2.5 and PM 10 were larger than those in southern China in all lag structures. An interquartile range increase in PM 2.5 and PM 10 in northern China corresponded to a 1.0% (95% confidence interval, 0.7%–1.4%) and 0.7% (95% confidence interval, 0.3%–1.2%) increase in ischemic stroke admissions at lag 3 days, respectively. For hemorrhagic stroke, no significant association was observed with PM in the 26 cities. Conclusions— This study suggests that short-term elevations in PM may increase the risk of ischemic but not hemorrhagic stroke. The associations of PM with ischemic stroke are stronger in northern China than in the south.