Particulate Matter and Hospital Admissions for Stroke in Beijing, China: Modification Effects by Ambient Temperature

Background-—The impact of particulate matter (PM) on stroke may vary by particle size, stroke subtype, and patient characteristics and temperature. We examined the association of stroke admissions with PM in different subgroups in Beijing, China, during 2013–2014. Methods and Results-—A time-stratified case-crossover design was used to assess the relation between PM of different particle sizes and hospital admissions for ischemic and hemorrhagic stroke. Stratified analyses were performed by age, sex, and temperature. In total, there were 147 624 stroke admissions during the study period. In the whole-period analysis, both PM_2.5 and PM₁₀ were positively associated with ischemic stroke admissions on the day of hospital admission and negatively associated with ischemic stroke at lag2 and lag3 day. In warm days (>13.5°C), the odds ratios of ischemic stroke admissions were 2.071 (95% CI 1.959–2.190), 1.470 (95% CI 1.391–1.554), and 1.590 (95% CI 1.493–1.694) per IQR increase in the same-day PM_2.5 (82.0 lg/ m³), PM_2.5–10 (36.6 lg/m³), and PM₁₀ (93.5 lg/m³), respectively. For hemorrhagic stroke, the corresponding values were 1.941 (95% CI 1.658–2.273), 1.590 (95% CI 1.366–1.851), and 1.527 (95% CI 1.278–1.826). The positive associations were also observed in the other lag structures and were higher than in cold days (≤13.5°C). Conclusions-—This study suggests that the associations of PM_2.5, PM_2.5–10, and PM₁₀ with stroke admissions differed across levels of temperature. Short-term exposure to PM_2.5, PM_2.5–10, and PM₁₀ was positively associated with hospital admissions for ischemic and hemorrhagic stroke on warm days (>13.5°C).