Air pollution and stroke hospitalization in the Beibu Gulf Region of China: A case-crossover analysis

BACKGROUND: The relationship between air pollution and stroke has been extensively studied, however, the evidence regarding the association between air pollution and hospitalization due to stroke and its subtypes in coastal areas of China is limited. OBJECTIVE: To estimate the associations between air pollution and hospitalizations of stroke and its subtypes in the Beibu Gulf Region of China. METHODS: We conducted a time-stratified case-crossover study in 15 cities in Beibu Gulf Region in China from 2013 to 2016. Exposures to PM(1), PM(2.5), PM(10), SO(2), NO(2), O(3), and CO on the case and control days were assessed at residential addresses using bilinear interpolation. Conditional logistic regressions were constructed to estimate city-specific associations adjusting for meteorological factors and public holidays. Meta-analysis was further conducted to pool all city-level estimates. RESULTS: There were 271,394 case days and 922,305 control days. The odds ratios (ORs) for stroke hospitalizations associated with each interquartile range (IQR) increase in 2-day averages of SO(2) (IQR: 10.8 µg/m(3)), NO(2) (IQR: 11.2 µg/m(3)), and PM(10) (IQR: 37 µg/m(3)) were 1.047 (95 % CI [confidence interval]: 1.015–1.080), 1.040 (95 % CI: 1.027–1.053), and 1.018 (95 % CI: 1.004–1.033), respectively. The associations with hospitalizations of ischemic stroke were significant for all seven pollutants, while the association with hemorrhagic stroke was significant only for CO. The associations of SO(2), NO(2), and O(3) with stroke hospitalization were significantly stronger in the cool season. CONCLUSIONS: Short-term increase in SO(2), NO(2), and PM(10) might be important triggers of stroke hospitalization. All seven air pollutants were associated with ischemic stroke hospitalization, while only CO was associated with hemorrhagic stroke hospitalization. These results should be considered in public health policy.