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 associated with asthma incidence. In models additionally adjusted for PM2.5 and NO2, UFPs exposure during the second trimester of pregnancy remained positively associated with childhood asthma incidence (HR per IQR increase = 1.05, 95% CI: 1.01 – 1.09).

Conclusion — 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 PM2.5 and NO2.