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

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 (NO 2 ), ozone (O 3 ), particulate matter 2.5, and sulfur dioxide (SO 2 ) exposure and 30-day all-cause hospital readmission in US fee-for-service Medicare beneficiaries age ≥65 years hospitalized for ischemic stroke in 2014 to 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 and Medicaid Services risk-standardized 30-day poststroke all-cause readmission measure to determine if the results were independent of performance: low (Centers for Medicare and Medicaid Services rate for hospital <25th percentile of national rate), high (>75th percentile), and intermediate (all others). Results: Of 448 148 patients with stroke, 12.5% were readmitted within 30 days. Except for tropospheric NO 2 (no national standard), average 2-year CO, O 3 , particulate matter 2.5, and SO 2 values were below national limits. Each one SD increase in average annual CO, NO 2 , particulate matter 2.5, and SO 2 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 O 3 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.