There is increasing recognition of the importance of early exposures in asthma development. Although outdoor air pollution has been identified as an asthma trigger, it is unclear whether exposure influences incident disease. We exploit the infrastructure of the Border Air Quality study to examine this question in an existing population-based cohort where follow up for respiratory health in the infant year has recently been reported.
Materials and Methods:
The birth cohort includes all children born in Southwestern British Columbia from 1999 to 2002. Incidence of asthma, wheeze, and related respiratory conditions at age 2 to 4 years will be assessed using hospitalization and outpatient records. Sex, birth weight, birth complications, number of siblings, maternal smoking during pregnancy, and socioeconomic status are available as covariates. Exposure to ambient air pollution has been estimated using high-resolution pollution surfaces that were developed using measurements from government monitoring stations or land use regression models adjusted for temporal variation. Poisson regression analyses will be used to estimate risk based on early life exposure. Subanalyses are planned to determine if changes in exposure due to relocation within the region affect the incidence or severity of respiratory conditions.
The total birth cohort includes 119,345 children. Follow-up data were available through 2003; 8280 (7%) received 2 outpatient diagnoses of asthma or 1 hospital diagnosis (our asthma case definition). Individuals were linked to the pollution surface by residential 6-digit postal code. Complete residential history was available for 70%. Thirty-five percent moved at least once within the follow up. Exposures were estimated for CO, NO, NO2, PM10, PM2.5, O3, SO2, black carbon, and woodsmoke.
This study makes efficient use of an existing large cohort and state of the art air pollution exposure assessment to explore the role of ambient air pollution in early life on development of wheezing phenotypes and asthma.