Timing and Duration of Traffic-related Air Pollution Exposure and the Risk for Childhood Wheeze and Asthma.

RATIONALE The timing and duration of traffic-related air pollution (TRAP) exposure may be important for childhood wheezing and asthma development. OBJECTIVES We examined the relationship between TRAP exposure and longitudinal wheezing phenotypes and asthma at age 7 years. METHODS Children completed clinical examinations annually from age 1 year through age 4 years and age 7 years. Parental-reported wheezing was assessed at each age, and longitudinal wheezing phenotypes (early-transient, late-onset, persistent) and asthma were defined at age 7 years. Participants' time-weighted exposure to TRAP, from birth through age 7 years, was estimated using a land-use regression model. The relationship between TRAP exposure and wheezing phenotypes and asthma was examined. MEASUREMENTS AND MAIN RESULTS High TRAP exposure at birth was significantly associated with both transient and persistent wheezing phenotypes (adjusted odds ratio [aOR] = 1.64; 95% confidence interval [CI], 1.04-2.57 and aOR = 2.31; 95% CI, 1.28-4.15, respectively); exposure from birth to age 1 year and age 1 to 2 years was also associated with persistent wheeze. Only children with high average TRAP exposure from birth through age 7 years were at significantly increased risk for asthma (aOR = 1.71; 95% CI, 1.01-2.88). CONCLUSIONS Early-life exposure to TRAP is associated with increased risk for persistent wheezing, but only long-term exposure to high levels of TRAP throughout childhood was associated with asthma development.