Outdoor Aeroallergen Impacts on Asthma Exacerbation Among Sensitized and Nonsensitized Philadelphia Children

This study aimed to estimate the association between pollens and molds and the risk for asthma exacerbation in patients with and without allergen sensitizations.The study population included children younger than 18 years diagnosed with asthma in the Children’s Hospital of Philadelphia from 2011 to 2016 who were living in Philadelphia at the time of the study.This study was a case-crossover design study examining outdoor allergen levels in relation to the odds of having an asthma exacerbation, defined by a diagnosis code of asthma and a systemic steroid prescription at the same visit. Data such as skin prick testing (SPT) results, age, type of insurance, atopic history, and medications was extracted from the patients’ electronic medical record. Aeroallergens were measured outdoors by the Asthma Center in Philadelphia on most weekdays from March through October using the Burkard volumetric spore trap, and spore counts were converted into air concentrations. An aeroallergen was included in the study if it appeared on more than 25% of the days. The relative odds of a patient having an asthma exacerbation was measured using a conditional logistic regression.Among the 13 891 children studied, there were a total of 28 540 asthma exacerbations, but only 5.5% of these children had a SPT reported. Of these, 60% had a positive test result to at least 1 outdoor aeroallergen. Asthma exacerbations were more likely to occur in male individuals, Black non-Hispanic children, those older than 5 years, children with private insurance, and those who had eczema and allergic rhinitis. Tree pollen was significantly associated with higher odds of asthma exacerbation in all patients, with larger odds in the early pollen season (March to June). In contrast, there was no association between grass pollen and exacerbation, even in sensitized children. Early weed pollens (August to October) correlated positively with exacerbations in sensitized individuals at the highest levels of pollen. Late weed pollens were not associated with exacerbations. In terms of molds, early-season (March to July) exposure did not show a consistent association with exacerbations overall; however, a nonmonotonic exposure-response pattern was seen with moderate mold levels only. In contrast, late-season (August to October) mold exposure was strongly associated with asthma exacerbations in sensitized children.Overall, the study concluded that children who were sensitized to specific allergens (tree pollens and molds) had higher odds of exacerbation following exposure to that particular allergen, as compared with nonsensitized and untested children. Allergens such as grasses and ragweed were not associated with asthma exacerbations, possibly due to low ambient levels or variability in the pollen counts in the area.This study reinforces the importance of SPT testing to identify potential environmental aeroallergens in children with asthma and highlights how sensitization status may influence the risk of asthma exacerbations during certain times of the year. A clinician’s knowledge of a patient’s sensitization status may facilitate tailored strategies for the management and prevention of asthma exacerbations, particularly during high-risk seasons.