Association of Annual Exposure to Air Pollution Mixture on Asthma Hospitalizations in the U.S.

Rationale: Air pollutants have adverse effects on asthma exacerbation in people of all ages. However, fewer studies have examined long-term exposure to particle components in conjunction with nitrogen dioxide (NO2) and ozone (O3) to assess their mixture effects. Objectives: We utilized weighted quantile sum (WQS) regression to assess the cumulative effects of 15 particle components including organ compounds and metals, along with NO2 and O3, on counts of inpatient asthma hospitalizations for children ages 0-18 and adults ages 19-64 years. Methods: We conducted two separate WQS models for each age group with weights constrained between 0-1 while summing up to 1, q=10 deciles, and 100 bootstrap samples. Measurements: Inpatient records for asthma hospitalizations were collected from State Inpatient Databases from 11 U.S. states ranging in years from 2002 through 2016. We also included temperature and variables from the U.S. census to control for socio-economic status. All variables were aggregated to the annual ZIP-code level. Main Results: We observed an increase of 10.6% (95%CI: 10.0%,11.2%) and 8.0% (95%CI: 7.7%,8.4%) in the number of asthma inpatient hospitalizations each year for each decile increase of the pollutant mixture in children ages 0 to 18 and adults ages 19 to 64, respectively. Nickel, Vanadium, sulfate, nitrate, Bromine, and ammonium contributed the most weight to the pollutant mixture. Conclusions: Our results indicate that long-term exposure to pollutant mixtures is associated with increased risk of asthma hospitalization in both children and adults, and daily measurements of particle components data is needed to assess short-term exposure.