Acute exposures to air pollutants and asthma hospitalization in the Medicaid population

Abstract

BACKGROUND AND AIM: Few studies have investigated roles of air pollutants on asthma among disadvantaged population. It is also unclear whether some sub-populations or communities experience disproportionate risk from air pollutants. METHODS: We estimated risk of asthma hospitalization associated with moving average exposures to particulate matter (PM2.5), ozone (O3), and nitrogen dioxide (NO2) over lag 0 to 6 days among all individuals enrolled in Medicaid, the largest health coverage to Americans with low income or disabilities, 2000–2012, using a time-stratified case-crossover design. To assess the risk at low levels, we restricted the analysis to hospitalizations with exposure below increasingly stringent thresholds, including those well below the national standards. Further, we performed subgroup analyses by individual- and community-level characteristics. RESULTS:We found positive associations between acute PM2.5, O3, and NO2 exposures and risk of asthma hospitalization: 1-µg/m3 increase in PM2.5, 1-part per billion (ppb) increase in O3, and 1-ppb increase in NO2 was associated with 0.31% (95% confidence interval [CI], 0.27%–0.36%), 0.11% (95% CI, 0.07%−0.15%), and 0.28% (95% CI, 0.25%−0.32%) increase in risk of asthma hospitalization, respectively. At low exposure levels, we found greater risk associated with PM2.5 and NO2. Further, we found consistently higher risk for the three exposures among beneficiaries with only one hospitalization during study period and communities with lower population density, higher average BMI, and longer distance to the nearest hospital. CONCLUSIONS:Our study adds to the existing body of research on acute effects of air pollutants on asthma, bridges the gaps in environmental health disparities, and is useful in informing policy. We found increased risk of asthma hospitalization associated with acute exposures to PM2.5, O3, and NO2 among Medicaid beneficiaries, even at levels well below the national standards. Subgroup analyses suggest that beneficiaries with mild to moderate symptoms and those living in disadvantaged communities experienced disproportionately higher risk from the pollutants. KEYWORDS: Mixtures, Short-term exposure, Asthma, Environmental disparities, Socio-economic factors