Spatiotemporal Variations in Ambient Ultrafine Particles and the Incidence of Childhood Asthma.

Abstract

<b>Rationale:</b> Little is known regarding the impact of ambient ultrafine particles (UFPs; <0.1 μm) on childhood asthma development. <b>Objectives:</b> To examine the association between prenatal and early postnatal life exposure to UFPs and development of childhood asthma. <b>Methods:</b> A total of 160,641 singleton live births occurring in the City of Toronto, Canada between April 1, 2006, and March 31, 2012, were identified from a birth registry. Associations between exposure to ambient air pollutants and childhood asthma incidence (up to age 6) were estimated using random effects Cox proportional hazards models, adjusting for personal- and neighborhood-level covariates. We investigated both single-pollutant and multipollutant models accounting for coexposures to particulate matter ≤2.5 μm in aerodynamic diameter (PM_2.5) and NO₂. <b>Measurements and Main Results:</b> We identified 27,062 children with incident asthma diagnosis during the follow-up. In adjusted models, second-trimester exposure to UFPs (hazard ratio per interquartile range increase, 1.09; 95% confidence interval, 1.06-1.12) was associated with asthma incidence. In models additionally adjusted for PM_2.5 and nitrogen dioxide, UFPs exposure during the second trimester of pregnancy remained positively associated with childhood asthma incidence (hazard ratio per interquartile range increase, 1.05; 95% confidence interval, 1.01-1.09). <b>Conclusions:</b> This is the first study to evaluate the association between perinatal exposure to UFPs and the incidence of childhood asthma. Exposure to UFPs during a critical period of lung development was linked to the onset of asthma in children, independent of PM_2.5 and NO₂.