Associations Between Long-Term Air Pollutant Exposure and 30-Day All-Cause Hospital Readmissions in US Stroke Patients.

Background: Long-term exposure to air pollutants is associated with increased stroke incidence, morbidity, and mortality; however, research on the association of pollutant exposure with poststroke hospital readmissions is lacking. Methods: We assessed associations between average annual carbon monoxide (CO), nitrogen dioxide (NO2), ozone (O3), particulate matter 2.5 (PM2.5), and sulfur dioxide (SO2) exposure and 30-day all-cause hospital readmission in US fee-for-service Medicare beneficiaries age ≥65 years hospitalized for ischemic stroke in 2014-2015. We fit Cox models to assess 30-day readmissions as a function of these pollutants, adjusted for patient and hospital characteristics and ambient temperature. Analyses were then stratified by treating hospital performance on the Centers for Medicare & Medicaid Services (CMS) risk-standardized 30-day poststroke all-cause readmission measure to determine if the results were independent of performance: low (CMS rate for hospital <25th percentile of national rate), high (>75th percentile), and intermediate (all others). Results: Of 448,148 stroke patients, 12.5% were readmitted within 30 days. Except for tropospheric NO2 (no national standard), average 2-year CO, O3, PM2.5, and SO2 values were below national limits. Each one standard deviation increase in average annual CO, NO2, PM2.5, and SO2 exposure was associated with an adjusted 1.1% (95% CI: 0.4-1.9%), 3.6% (95% CI 2.9%-4.4%), 1.2% (95% CI: 0.2%-2.3%), and 2.0% (95% CI 1.1%-3.0%) increased risk of 30-day readmission, respectively, and O3 with a 0.7% (95% CI: 0.0%-1.5%) decrease. Associations between long-term air pollutant exposure and increased readmissions persisted across hospital performance categories. Conclusions: Long-term air pollutant exposure below national limits was associated with increased 30-day readmissions after stroke, regardless of hospital performance category. Whether air quality improvements lead to reductions in poststroke readmissions requires further research.