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

¹ Department of Pediatrics, ² Department of Environmental and Occupational Health Sciences, University of Washington, Seattle, Washington; ³ School of Environmental Health, ⁴ School of Population and Health, and ⁵ Centre for Health Services and Policy Research, The University of British Columbia, Vancouver, Canada

Correspondence and requests for reprints should be addressed to Catherine J. Karr, M.D., Ph.D., M.S., Pediatrics/Occupational & Environmental Medicine, University of Washington, 401 Broadway, Box 359739, Seattle, WA 98104. E-mail: ckarr{at}u.washington.edu

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 µm or less (PM_2.5), PM₁₀, NO₂/NO, SO₂, CO, and O₃ 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, PM_2.5, 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 [OR_adj] NO₂, 95% confidence interval [CI], 1.12, 1.09–1.16; OR_adj 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, PM_2.5, 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.

Key Words: bronchiolitis • wood smoke • traffic • air pollution • respiratory disease

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Ambient air pollution has been associated with several adverse respiratory health outcomes in children and adults. Bronchiolitis is the leading cause of hospitalization in the first year of life in North America, yet data regarding the role of ambient air pollution are few. What This Study Adds to the Field This study provides evidence that traffic-derived, industrial-point source, and wood smoke–related exposures may increase the burden bronchiolitis in infants.