Nationwide Study of Short-term Exposure to Fine Particulate Matter and Cardiovascular Hospitalizations Among Medicaid Enrollees

Background: Fine particulate matter (PM2.5) has been consistently linked to cardiovascular disease (CVD). Although studies have reported modification by income, to our knowledge, no study to date has examined this relationship among adults in Medicaid, which provides health coverage to low-income and/or disabled Americans. Methods: We estimated the association between short-term PM2.5 exposure (average of PM2.5 on the day of hospitalization and the preceding day) and CVD admissions rates among adult Medicaid enrollees in the continental United States (2000-2012) using a time-stratified case-crossover design. We repeated this analysis at PM2.5 concentrations below the World Health Organization daily guideline of 25 mu g/m(3). We compared the PM2.5-CVD association in the Medicaid >= 65 years old versus non-Medicaid-eligible Medicare enrollees (>= 65 years old). Results: Using information on 3,666,657 CVD hospitalizations among Medicaid adults, we observed a 0.9% (95% CI = 0.6%, 1.1%) increase in CVD admission rates per 10 mu g/m(3) PM2.5 increase. The association was stronger at low PM2.5 levels (1.3%; 95% CI = 0.9%, 1.6%). Among Medicaid enrollees >= 65 years old, the association was 0.9% (95% CI = 0.6%, 1.3%) vs. 0.8% (95% CI = 0.6%, 0.9%) among non-Medicaid-eligible Medicare enrollees >= 65 years old. Conclusion: We found robust evidence of an association between short-term PM2.5 and CVD hospitalizations among the vulnerable subpopulation of adult Medicaid enrollees. Importantly, this association persisted even at PM2.5 levels below the current national standards.