The relationship between pollen, air pollution, and asthma exacerbations in children in Allegheny County, PA from 2003-2011: a case-crossover analysis

Background: Asthma is a common chronic disease among children in the US. Prevalence is increasing, and asthma exacerbations have major impacts on the lives of children and their families. Understanding the role of outdoor pollen as an asthma trigger is important to developing clinical and public health interventions to improve asthma outcomes. 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 for children age 5-17 in Allegheny County from April to October 2003-2011. Since the effects of environmental triggers on asthma may occur over several days, we investigated the effects of pollen and pollution levels on the day of the ED visit, as well as lags of 1, 2, 3, 4, and 5, and averages of day 0-2 and day 0-5. We examined single pollutant and single pollen models adjusted for apparent maximum temperature, as well as multivariable models controlling for all pollens, pollutants, and apparent maximum temperature. Results: During the study period there were 8,711 asthma ED visits. 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 for the average of lag days 0-2 for tree pollen (OR = 1.016, 95% CI 1.007-1.024) and the average of lag days 0-5 for weed pollen (OR = 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. Discussion: This research builds on previous work in Allegheny County demonstrating the impact of air pollution on asthma ED visits. By further considering pollen levels, we demonstrated that high tree and weed pollen levels appear to be associated with asthma ED visits in children, independent of air pollution levels. The public health significance of these findings is that implementing methods to control allergen exposure during particular seasons may prevent adverse asthma outcomes