Post-Discharge Exposure to Ambient Sulfur Dioxide is Associated with Increased Risk of Stroke Recurrence

Background and Purpose: Ambient air pollution is an established risk factor for incident stroke, but whether post-discharge pollutant exposure influences stroke recurrence remains unknown. We investigated the association between post-discharge exposure to six ambient air pollutants and stroke recurrence in patients with acute ischemic stroke. Methods: We analyzed data from 27,346 patients in the CRCS-K-NIH nationwide multicenter registry of acute ischemic stroke patients (2014-2021) with confirmed ischemic stroke, residential address data, and matched air quality records. The primary exposure was the 3-month post-discharge average concentration of PM10, PM2.5, NO2, SO2, CO, and O2, assessed at the district level using inverse-distance weighted interpolation. The primary outcome was stroke recurrence from 3 to 15 months post-discharge. Cause-specific Cox proportional hazards models accounting for the multilevel data structure were used, with all-cause mortality as a competing risk. Restricted cubic splines assessed nonlinear dose-response relationships. Results: During follow-up (median 364.8 days), 765 patients experienced stroke recurrence and 471 died. Among the six pollutants, only SO2 showed a statistically significant association with recurrence (P for overall association in the restricted cubic spline analysis = 0.024). A potential threshold was identified at approximately 8.2 ppb, above which recurrence risk increased progressively (P for non-linearity = 0.095). 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), consistent with maritime shipping emissions. No significant associations were observed for the other five pollutants. Conclusions: Elevated post-discharge SO? exposure is associated with increased stroke recurrence risk, particularly in harbor regions and among older adults and women. These findings support incorporating ambient air quality monitoring into secondary stroke prevention strategies.