PM2.5 and 30-Day Readmission in Medicare Beneficiaries with Alzheimer’s Disease and Related Dementias: Effect Modification by Neighborhood Green and Blue Space

Hospital readmissions are a major concern among people living with Alzheimer’s disease and related dementias (ADRD), contributing to substantial burden on patients, caregivers, and health care systems. We evaluated whether short-term exposure to fine particulate matter (PM2.5) was associated with 30-day all-cause readmission among older adults with ADRD and whether residential green and blue space modified this association. We conducted a nationwide time-stratified case-crossover study using Medicare fee-for-service inpatient claims from 2000 to 2016 in the contiguous United States. We identified 30-day all-cause readmissions following the first index admission with ADRD. Daily modeled PM2.5 concentrations were linked to residential ZIP Codes, and exposure windows up to lag 2 days were examined. Measures of green and blue space were derived from Landsat and Google Street View data. Conditional logistic regression was used to estimate associations between PM2.5 and readmission with interaction terms used to evaluate effect modification by levels of green and blue space. Among 6,098,836 beneficiaries with an index admission with ADRD, 759,128 (12.4%) experienced a 30-day all-cause readmission. An interquartile range (IQR; 7.2 μg/m3) increase in PM2.5 averaged over lag 0 to 2 days was associated with a higher risk of readmission (odds ratio: 1.010; 95% confidence interval: 1.006, 1.015). Associations were higher for beneficiaries with longer intervals to readmission (>7 days). Effect modification by green or blue space was not conclusive. These findings suggest that short-term PM2.5 exposure may increase the risk of 30-day all-cause hospital readmission among Medicare beneficiaries with ADRD. Reducing ambient PM2.5 exposure may help prevent avoidable readmissions and lessen burden on patients, caregivers, and health care systems.