The Relationship between Pollen, Air Pollution, and Asthma Exacerbations in Children in Allegheny County, Pennsylvania: A Case-Crossover Analysis

Abstract

Background: Asthma is a common chronic disease among children in the US. Outdoor air pollutants have been linked to asthma exacerbations but fewer studies have been conducted to examine the association between outdoor levels of pollens and asthma outcomes in children.Methods: Time-stratified case-crossover design with conditional logistic regression was used to study the short-term effects of three major pollens (grass, tree, and weed) and four criteria pollutants (PM 2.5, Ozone, SO2, and NO2) on asthma Emergency Department (ED) visits in children age 5-17 reported in Allegheny County, Pennsylvania from April to October 2003-2011. Multivariable models controlling for all pollens, all pollutants, and apparent maximum temperature were conducted to investigate the effects of pollen and pollutant levels on the day of the ED visit, lags of day 1, 2, 3, 4, and 5, and averages of day 0-2 and day 0-5.Results: A total of 8,711 asthma ED visits were reported during the study period. In multivariable models, tree and weed pollen were significant positive predictors of asthma ED visits across multiple lags when controlling for temperature and air pollutants. Strongest effects were reported on the average of lag days 0-2 for tree pollen (Odds Ratio = 1.016, 95% CI 1.007-1.024) and the average of lag days 0-5 for weed pollen (Odds Ratio = 1.044, 95% CI 1.026-1.062). PM 2.5 and NO2 were also significantly positively associated with ED visits across multiple lags, whereas SO2 was negatively associated with ED visits at several lags.Conclusions: This study reported that higher tree and weed pollen levels were associated with increased odds of asthma ED visits in children, independent of air pollution levels. Implementing methods to control allergen exposure during particular seasons may prevent adverse asthma outcomes.