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

Rationale: Little is known regarding the impact of ambient ultrafine particles (<0.1 μm) (UFPs) on childhood asthma development. Objective: To examine the association between prenatal and early postnatal life exposure to UFPs and development of childhood asthma. Methods: A total of 160,641 singleton live births occurring in the City of Toronto, Canada between April 1st 2006 and March 31st 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- and multi-pollutant models accounting for co-exposures to PM2.5 and NO2. Measurements and Main Results: We identified 27,062 children with incident asthma diagnosis during the follow-up. In adjusted models, second trimester exposure to UFPs (Hazard Ratio (HR) per interquartile (IQR) increase = 1.09, 95% CI: 1.06 - 1.12) was ...