Associations between ambient air pollution, meteorology, and daily hospital admissions for ischemic stroke: a time-stratified case-crossover study in Beijing

Air pollution and ischemic stroke (IS) are both vital factors affecting the health of Beijing citizens. This study aims at exploring the associations between air pollution, meteorology, and the hospital admission of IS (IS HA). Information on 476,659 IS inpatients in secondary and higher hospitals in Beijing from 2013 to 2018 were collected. A time-stratified case-crossover design with the generalized additive model and the distributed lag nonlinear model were used. In the single-pollutant models, an inter-quartile range increase in O 3, SO 2 , CO, and NO 2 resulted in a significant highest increase in IS HA by 2.23% (95% CI : 1.56%, 2.90%), 1.53% (95% CI : 1.12%, 1.95%), 1.05% (95% CI : 0.70%, 1.40%), and 0.51% (95% CI : 0.24%, 0.79%) on the day of pollution, so did PM 2.5 and PM 10 by 1.13% (95% CI : 0.68%, 1.59%) and 1.19% (95% CI : 0.74%, 1.64%) at a lag of 0–5 days. There was a nonlinear relationship between meteorology and IS HA. In the multivariate model, the cumulative relative risks with a maximum lag time of 21 days of PM 2.5 and NO 2 were 1.11 (95% CI : 1.04, 1.19) and 0.88 (95% CI : 0.82, 0.94), while the effects of SO 2 , O 3 , and meteorology were insignificant. The findings suggested that particulate pollutants could increase the risk of IS, and the elderly were more sensitive to it, while the results of gaseous pollutants are still discordant. The control of air pollution and the protection of susceptible populations should receive higher attention from policymakers.