The Effects of Fine Particle Components on Respiratory Hospital Admissions in Children

Background: Epidemiologic studies have demonstrated an association between acute exposure to ambient fine particles and both mortality and morbidity. Less is known about the relative impacts of the specific chemical constituents of particulate matter < 2.5 μm in aerodynamic diameter$({\rm PM}_{2.5})$on hospital admissions. Objective: This study was designed to estimate the risks of exposure to${\rm PM}_{2.5}$and several species on hospital admissions for respiratory diseases among children. Data and methods: We obtained data on daily counts of hospitalizations for children < 19 and < 5 years of age for total respiratory diseases and several subcategories including pneumonia, acute bronchitis, and asthma for six California counties from 2000 through 2003, as well as ambient concentrations of${\rm PM}_{2.5}$and its constituents, including elemental carbon (EC), organic carbon (OC), and nitrates (NO₃). We used Poisson regression to estimate risks while controlling for important covariates. Results: We observed associations between several components of${\rm PM}_{2.5}$and hospitalization for all of the respiratory outcomes examined. For example, for total respiratory admissions for children < 19 years of age, the interquartile range for a 3-day lag of${\rm PM}_{2.5}$, EC, OC, NO₃, and sulfates was associated with an excess risk of 4.1% [95% confidence interval (CI), 1.8-6.4], 5.4% (95% CI, 0.8-10.3), 3.4% (95% CI, 1.1-5.7), 3.3% (95% CI, 1.1-5.5), and 3.0% (95% CI, 0.4-5.7), respectively. We also observed associations for several metals. Additional associations with several of the species, including potassium, were observed in the cool season. Conclusion: Components of${\rm PM}_{2.5}$were associated with hospitalization for several childhood respiratory diseases including pneumonia, bronchitis, and asthma. Because exposure to components (e.g., EC, OC, NO₃, and K) and their related sources, including diesel and gasoline exhaust, wood smoke, and other combustion sources, are ubiquitous in the urban environment, it likely represents an identifiable and preventable risk factor for hospitalization for children.