Association of Annual Exposure to Air Pollution Mixture on Asthma Hospitalizations in the United States

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 used weighted quantile sum regression to assess the cumulative effects of 15 particle components, including organic compounds and metals, together with NO₂ and O₃, on counts of inpatient asthma hospitalizations for children 0–18 years of age and adults 19–64 years of age. Methods: We conducted two separate weighted quantile sum models for each age group, with weights constrained between 0 and 1 while summing up to 1, q = 10 deciles, and 100 bootstrap samples. Measurements and Main Results: Inpatient records for asthma hospitalizations from 2002 to 2016 were collected from 11 U.S. state inpatient databases. We also included temperature and variables from the U.S. census to control for socioeconomic status. All variables were aggregated to the annual ZIP code level. We observed an increase of 10.6% (95% confidence interval, 10.0–11.2%) and 8.0% (95% confidence interval, 7.7–8.4%) in the number of asthma inpatient hospitalizations each year for each decile increase of the pollutant mixture in children 0–18 years of age and adults 19–64 years of age, respectively. Nickel, vanadium, sulfate, nitrate, bromine, and ammonium contributed the most weight to the association found. 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 are needed to assess short-term exposure.