Atopy at age 1 and traffic-related Air pollution: an investigation of exposure measures in the Canadian Health Infant Longitudinal Development (CHILD) birth coh

Abstract

Background: The evidence for increased risk of sensitization in children due to traffic related air pollution (TRAP) exposure is equivocal and information from birth cohorts with spatiotemporal exposure assessment is rare. Aims: We used atopy data at age 1 from an ongoing birth cohort (CHILD) and land use regression (LUR) estimates of individual exposure to nitrogen dioxide (NO2) to examine the association between TRAP and sensitization in four Canadian cities. Methods: We identified 885 children who were ? one year old on July 31st, 2012 and with measurement of atopy for inhalant (Alternaria, Der p, Der f, Cat, Dog, Cockroaches) and food-related allergens (soybean, milk, peanuts, eggs). Participants with epicutaneous skin test 2mm greater than negative control were defined as atopic.Exposure was estimated from city-specific LUR models with and without bi-weekly temporal adjustment based on fixed-site monitoring network data. We examined sex, study center, SES, maternal smoking/atopy/asthma, siblings, pets, mold, and secondhand smoke exposure as covariates. Those showing significant associations with atopy were offered in mixed models evaluating TRAP exposure during pregnancy and the first year of life. Results: Within-city contrasts in TRAP exposure in utero and during the first year of life was positively associated with sensitization to inhalant allergens at age one (adj. OR [95%CI]: 2.16 [1.17 -4.04], 2.15[1.21 -3.71] per 10 ppb increase, for in utero and year 1, respectively). Temporal adjustments of LUR estimates led to increased odds ratios for both time windows with a more pronounced effect during the first year of life (2.6 [1.4 -4.8] and 3.3 [1.7 – 6.7], for in utero and year 1, respectively). Conclusion: Early-life TRAP exposure was associated with risk of sensitization. Increased specificity in exposure assessment increases effect estimates.