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Exposure to Traffic-related Particles and Endotoxin during Infancy Is Associated with Wheezing at Age 3 Years

¹ Department of Environmental Health, and ² Department of Internal Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio; and ³ Department of Allergy and Immunology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio

Correspondence and requests for reprints should be addressed to Patrick H. Ryan, Ph.D., 3223 Eden Ave, PO Box 670056, Cincinnati, OH 45267-0056. E-mail: patrick.ryan{at}uc.edu

Rationale: Murine models demonstrate a synergistic production of reactive oxygen species on coexposure to diesel exhaust particles and endotoxin.

Objectives: It was hypothesized that coexposure to traffic-related particles and endotoxin would have an additive effect on persistent wheezing during early childhood.

Methods: Persistent wheezing at age 36 months was assessed in the Cincinnati Childhood Allergy and Air Pollution Study, a high-risk birth cohort. A time-weighted average exposure to traffic-related particles was determined by applying a land-use regression model to the homes, day cares, and other locations where children spent time from birth through age 36 months. Indoor levels of endotoxin were measured from dust samples collected before age 12 months. The relationship between dichotomized (</75th percentile) traffic-related particle and endotoxin exposure and persistent wheezing, controlling for potential covariates, was examined.

Measurements and Main Results: Persistent wheezing at age 36 months was significantly associated with exposure to increased levels of traffic-related particles before age 12 months (OR = 1.75; 95% confidence interval, 1.07–2.87). Coexposure to endotoxin had a synergistic effect with traffic exposure on persistent wheeze (OR = 5.85; 95% confidence interval, 1.89–18.13) after adjustment for significant covariates.

Conclusions: The association between traffic-related particle exposure and persistent wheezing at age 36 months is modified by exposure to endotoxin. This finding supports prior toxicological studies demonstrating a synergistic production of reactive oxygen species after coexposure to diesel exhaust particles and endotoxin. The effect of early versus later exposure to traffic-related particles, however, remains to be studied because of the high correlation between exposure throughout the first 3 years of life.

Key Words: particles • diesel • land-use regression • wheeze • endotoxin

AT A GLANCE COMMENTARY Scientific Knowledge on the Subject Prior studies suggest that exposure to diesel exhaust particles (DEP) results in the production of reactive oxygen species (ROS). Previous studies of traffic-related pollution and wheezing during childhood have not examined exposure during early infancy to traffic-related particles in combination with indoor endotoxin, which may lead to increased persistent wheezing in at-risk children. What This Study Adds to the Field This study provides evidence that exposure to traffic-related particles is associated with childhood wheeze and that a synergistic relationship exists between coexposure to traffic-related particles and endotoxin during infancy and persistent wheezing at age 3 years.

 

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