Post-Discharge Ambient Sulfur Dioxide Exposure and Stroke Recurrence After Acute Ischemic Stroke

BACKGROUND AND PURPOSE: Ambient air pollution is an established risk factor for incident stroke, but whether post-discharge pollutant exposure influences stroke recurrence remains unclear. We investigated the association between post-discharge exposure to six ambient air pollutants and stroke recurrence after acute ischemic stroke. METHODS: We analyzed 27,340 patients in the Clinical Research Collaboration for Stroke in Korea-National Institutes of Health nationwide multicenter registry (2014-2021). The 3-month post-discharge district-level mean concentrations of particulate matter ≤10 μm (PM10), ≤2.5 μm (PM2.5), nitrogen dioxide, sulfur dioxide (SO2), carbon monoxide, and ozone were estimated by inverse-distance-weighted interpolation. The primary outcome was stroke recurrence from 3 to 15 months post-discharge. Cause-specific Cox models with cluster-robust standard errors were used, treating death as a competing risk; non-linear dose-response was assessed by restricted cubic splines. RESULTS: During follow-up (median 364.8 days), 764 patients had recurrence and 542 died. Only SO2 showed a significant association with recurrence (P for overall association in the spline model= 0.024), with a graded dose-response; the non-linear (J-shaped) pattern did not reach significance (P for non-linearity=0.095), and quartile contrasts were individually non-significant (Q4 vs. Q1: hazard ratio 1.19, 95% confidence interval 0.94-1.50). The association was numerically stronger among older adults (≥75 years; P for interaction=0.051) and women (P for interaction=0.062). The highest SO2 concentrations were observed in harbor cities (Incheon, Ulsan, Busan). No significant associations were observed for the other five pollutants. CONCLUSIONS: Elevated post-discharge SO2 exposure was associated with increased stroke recurrence, with a graded dose-response, supporting consideration of ambient air quality in secondary stroke prevention.