LAUSR

BACKGROUND Short-term changes in ambient fine particulate matter (PM2.5) increase the risk for unplanned hospital readmissions. However, this association has not been fully evaluated for high-risk patients or examined to determine if the readmission risk differs based on time since discharge. Here we investigate the relation between ambient PM2.5 and 30-day readmission risk in heart failure (HF) patients using daily time windows and examine how this risk varies with respect to time following discharge. METHODS We performed a retrospective cohort study of 17,674 patients with a recorded HF diagnosis between 2004 and 2016. The cohort was identified using the EPA CARES electronic health record resource. The association between ambient daily PM2.5 (μg/m3) concentration and 30-day readmissions was evaluated using time-dependent Cox proportional hazard models. PM2.5 associated readmission risk was examined throughout the 30-day readmission period and for early readmissions (1-3 days post-discharge). Models for 30-day readmissions included a parametric continuous function to estimate the daily PM2.5 associated readmission hazard. Fine-resolution ambient PM2.5 data were assigned to patient residential address and hazard ratios are expressed per 10 μg/m3 of PM2.5. Secondary analyses examined potential effect modification based on the time after a HF diagnosis, urbanicity, medication prescription, comorbidities, and type of HF. RESULTS The hazard of a PM2.5-related readmission within three days of discharge was 1.33 (95% CI 1.18-1.51). This PM2.5 readmission hazard was slightly elevated in patients residing in non-urban areas (1.43, 95%CI 1.22-1.67) and for HF patients without a beta-blocker prescription prior to the readmission (1.35; 95% CI 1.19-1.53). CONCLUSION Our findings add to the evidence indicating substantial air quality-related health risks in individuals with underlying cardiovascular disease. Hospital readmissions are key metrics for patients and providers alike. As a potentially modifiable risk factor, air pollution-related interventions may be enacted that might assist in reducing costly and burdensome unplanned readmissions.