Influence Of Acute Air Pollution Exposure On Infant Bronchiolitis Clinical Encounters

Abstract

Introduction: Particulate matter less than 2.5µm in diameter (PM2.5) can alter immune function making individuals, especially infants, more susceptible to illness. The objective of this analysis is to determine if short-term exposure to PM2.5 is associated with risk of a clinical encounter for infant bronchiolitis. Methods: We analyzed 26,861 first time bronchiolitis clinical encounters among infants less than 12 months of age born between 2000 -2009. We used case-cross over conditional logistic regression models adjusted for temperature, humidity, atmospheric pressure, and holiday using a semi-symmetric bidirectional referent design. We examined the influence of PM2.5 on (1) symptom exacerbation using very short exposure lags of 0 and 1 day and (2) susceptibility to infection using longer exposure lags of 4 and 7 days. PM2.5 exposure was modeled using daily satellite remote sensing data based on geocoded birth address. We assessed effect modification by gestational age, birth weight, fetal growth, season of diagnosis, and bronchiolitis frequency to determine susceptibility. Results: We found that a 10 µg increase of PM2.5 was positively associated with bronchiolitis clinical encounter risk 1 and 4 days after exposure (lag1 Odds Ratio (OR) =1.05; 95% Confidence Interval (CI): 1.02, 1.08; lag 4 OR=1.04; 95%CI: 1.01, 1.06). The association between PM2.5 exposure and bronchiolitis clinical encounters was significantly different between cold and warm seasons (lag1 p=0.004; lag 4 p= 0.009) with positive associations in cold seasons but not in warm seasons. We did not observe strong evidence of effect modification by gestational age, birth weight, fetal growth, or clinical encounter frequency. Conclusions: We observed an increased risk of bronchiolitis diagnosis one and four days prior to acute PM2.5 exposure. This suggests that exposure to PM2.5 may play a role in both bronchiolitis susceptibility and symptom exacerbation.