PM2.5 Exposure and Risk of Hospitalization for Infant Bronchiolitis

Abstract

SM4-PD-08 Introduction: We recently reported a positive association between lifetime PM2.5 exposure and risk of infant bronchiolitis in a high-pollution region of the United States. We sought to further examine this question, as well as differing exposure windows, in a U.S. population with moderate particulate matter pollution as part of the Border Air Quality Study. Methods: Subjects were derived from linked birth record-hospital discharge records of infants born in 1997 to 2002. Cases (a hospital discharge record for bronchiolitis in infancy) were randomly matched to 10 controls without this diagnosis based on date of birth, length of birth hospitalization, and gestational age. Short-term (7, 14 days), subchronic (30, 60 days), and lifetime mean exposures referenced prior to the case diagnosis date were assessed based on regulatory network monitoring data (proximal monitor within 20 km). Risk estimates for an increase in PM2.5 of 10 μg/m3 and quartiles of exposure were estimated using conditional logistic regression. Results: A total of 770 case infants and 24,009 controls were assigned exposure. Their mean (SD) distance to a PM2.5 monitor was 8.1 km (4.7). The 7-, 14-, 30-, and 60-day and lifetime mean (SD) concentrations of PM2.5 were 11.9 (5.3), 12.1 (4.5), 12.3 (4.0), 12.8 (3.8), and 12.3 (3.3) μg/m3, respectively. We found no statistically significant increased risk for infant bronchiolitis with any of the exposure windows investigated, after adjustment for confounders (sex, mother smoking during pregnancy, mother's education, parity, insurance and benefits type, infant race/ethnicity). Risk estimates were highest for lifetime exposure (OR; 95% CI per 10 μg/m3 increase, 1.07; 0.83–1.36). This estimate increased with restriction to subjects with monitors within 5 km (1.25; 0.72-2.17) or to subjects with a diagnosis of bronchiolitis due to respiratory syncytial virus (RSV), specifically (1.17; 0.88–1.56). Discussion and Conclusions: For North American infants, bronchiolitis is the leading cause of hospitalization and RSV is the most important etiologic agent. In contrast to our findings in a high pollution region, this study did not find a statistically significant association with chronic PM2.5 exposure. Discrepancies may reflect differences in concentrations and composition of particulate matter and monitoring network density in the 2 regions. Sensitivity analyses based on refined exposure assessment (closer monitors) and case definition (RSV) were consistent with previous findings of higher risk estimates for chronic exposure windows compared with shorter-term exposures. Our next steps include using spatial modeling of traffic and woodsmoke exposure to improve the assessment of chronic particulate air pollution in this study population.