Influence of Ambient Air Pollutant Sources on Clinical Encounters for Infant Bronchiolitis

Rationale: Data regarding the influence of ambient air pollution on infant bronchiolitis are few. Objectives: We evaluated the impact of several air pollutants and their sources on infant bronchiolitis. Methods: Infants in the Georgia Air Basin of British Columbia with an inpatient or outpatient clinical encounter for bronchiolitis (n = 11,675) were matched on day of birth to as many as 10 control subjects. Exposure to particulate matter with a diameter of 2.5 mu m or less (PM2.5), PM10, NO2/NO, SO2, CO, and O-3 were assessed on the basis of a regional monitoring network. Traffic exposure was assessed using regionally developed land use regression (LUR) models of NO2, NO, PM2.5, and black carbon as well as proximity to highways. Exposure to wood smoke and industrial emissions was also evaluated. Risk estimates were derived using conditional logistic regression and adjusted for infant sex and First Nations (Canadian government term for recognized aboriginal groups) status and for maternal education, age, income-level, parity, smoking during pregnancy, and initiation of breastfeeding. Measurements and Main Results: An interquartile increase in lifetime exposure to NO2, NO, SO2, CO, wood-smoke exposure days, and point source emissions score was associated with increased risk of bronchiolitis (e.g., adjusted odds ratio [ORadj] NO2, 95% confidence interval [CI], 1.12,1.09-1.16; ORadj wood smoke, 95% CI, 1.08,1.04-1.11). Infants who lived within 50 meters of a major highway had a 6% higher risk (1.06, 0.97-1.17). No adverse effect of increased exposure to PM10, PM2.5, or black carbon, was observed. Ozone exposure was negatively correlated with the other pollutants and negatively associated with the risk of bronchiolitis. Conclusions: Air pollutants from several sources may increase infant bronchiolitis requiring clinical care. Traffic, local point source emissions, and wood smoke may contribute to this disease.