Association between ambient air pollution and hospitalization for ischemic and hemorrhagic stroke in China: A multicity case-crossover study

- First multicity study in China about the effect of air pollution on stroke morbidity.
- PM10, NO2, SO2, CO, and O3 exposures were positively associated with ischemic stroke.
- NO2 exposure may account for increased hemorrhagic stroke hospitalizations.

There is growing interest in the association between ambient air pollution and stroke, but few studies have investigated the association in developing countries. The primary objective of this study was to examine the association between levels of ambient air pollutants and hospital admission for stroke in China. A time-stratified case-crossover analysis was conducted between 2014 and 2015 in 14 large Chinese cities among 200,958 ischemic stroke and 41,746 hemorrhagic stroke hospitalizations. We used conditional logistic regression to estimate the percentage changes in stroke admissions in relation to interquartile range increases in air pollutants. Air pollution was positively associated with ischemic stroke. A difference of an interquartile range of the 6-day average for particulate matter less than 10 μm in aerodynamic diameter, sulfur dioxide, nitrogen dioxide, carbon monoxide, and ozone corresponded to 0.7% (95% CI: 0%, 1.4%), 1.6% (95% CI: 1.0%, 2.3%), 2.6% (95% CI: 1.8%, 3.5%), 0.5% (95% CI: −0.2%, 1.1%), and 1.3% (95% CI: 0.3%, 2.3%) increases in ischemic stroke admissions, respectively. For hemorrhagic stroke, we observed the only significant association in relation to nitrogen dioxide on the current day (percentage change: 1.6%; 95% CI: 0.3%, 2.9%). Our findings contribute to the limited scientific literature concerning the effect of ambient air pollution on stroke in developing countries. Our findings may have significant public health implications for primary prevention of stroke in China.

Percentage change (95% CI) in hospital admissions for ischemic stroke and hemorrhagic stroke associated with a difference of an interquartile range (IQR) of PM10 (85.7 μg/m3), NO2 (25.4 μg/m3), SO2 (38.3 μg/m3), CO (0.81 mg/m3), and O3 (67 μg/m3) for different lag structures in 14 Chinese cities, 2014-2015. PM10, particulate matter less than 10 μm in aerodynamic diameter; NO2, nitrogen dioxide; SO2, sulfur dioxide; CO, carbon monoxide; O3, ozone.183