Short-term exposure to ambient PM _2.5 and PM ₁₀ is associated with increased risk of mortality and hospital admissions for stroke. However, there is less evidence regarding the effect of exposure to PM ₁ on stroke incidence. We estimated the incidence risk of stroke and the attributable fractions related to short-term exposure to ambient PM ₁ , PM _2.5 and PM ₁₀ in China.
County-specific incidence of stroke was obtained from health statistics in years 2014-2019. We linked county-level mean daily concentrations of PM ₁ , PM _2.5 and PM ₁₀ with stroke incidence. We used the time stratified case-crossover design to estimate the associations between stroke incidence and exposure to PM ₁ , PM _2.5 and PM ₁₀ . We also estimated the disease burden fractions attributable to PM ₁ , PM _2.5 , and PM ₁₀ .
The study included a total of 2,193,954 stroke, from which 1,861,331 were ischemic and 332,623 were hemorrhagic stroke. PM ₁ , PM _2.5 , and PM ₁₀ levels were associated with increased risks of total stroke and ischemic stroke at when assessing the associations in exposure at lag0-4 days. The increase of 10 μg/m ³ in PM ₁ , PM _2.5 , and PM ₁₀ was associated with total stroke, and the relative risks were 1.012 (95% confidence interval: 1.008, 1.015), 1.006 (1.004, 1.007) and 1.003 (1.002, 1.004), while the associations with ischemic stroke were 1.013 (1.010, 1.017), 1.006 (1.005, 1.008) and 1.003 (1.002, 1.004), respectively. There was no significant association between PM and risk of hemorrhagic stroke. The attributable fractions of total stroke were 6.9% (5.1%, 8.5%), 5.6% (4.2%, 6.8%) and 5.6% (3.9%, 7.1%) for PM ₁ , PM _2.5 , and PM ₁₀ , respectively.
PM ₁ showed a stronger association with stroke, with a larger attributable fraction of outcomes, than PM _2.5 and PM ₁₀ . Clean air policies should target the whole scope of PM, including PM ₁ .