Air Quality Index and Emergency Department Visits and Hospitalizations in Children with Asthma: A Time-Stratified Case-Crossover Study in Pittsburgh

Introduction: Outdoor air pollution is a known cause of childhood asthma exacerbations.In the United States, the Air Quality Index (AQI) is meant to alert the public to air quality and provide behavioral recommendations to reduce risk of harm.The association between the AQI and severe asthma exacerbations in US children is unknown.Methods: Using medical record data from UPMC Children's Hospital of Pittsburgh for 2010-2018, we conducted a time-stratified case-crossover study of emergency department (ED) visits and hospitalizations with a primary diagnosis code of asthma exacerbation for children aged 6 to 17 years.Environmental Protection Agency air quality data was obtained as daily overall AQI and for each of 5 criteria pollutants.AQI values on the day of event and the preceding 5 days (lag days) were evaluated.Conditional logistic regression was used for analyses, adjusting for meteorological variables.Effect modification was evaluated by stratification.Results: There were 6,573 events from 3,344 unique persons.The average age at time of event was 10 years; 57.2% were Black and 58.7% were male.Most events (n=4,431 (67.4% of total) occurred in 35.9% of persons.Particulate matter <2.5m (PM 2.5 ) was primarily responsible for the overall AQI, followed by ozone, and sulfur dioxide (61%, 29%, and 8% of days with events respectively).Half of all days were in the 'Moderate' category, (49%) followed by 'Good' (41.5%); fewer were in 'Unhealthy for Sensitive Groups' (8.5%) or 'Unhealthy' (1.1%).Overall AQI category in the prior 2 days was associated with increased odds of ED visits/hospitalizations (lag day 2: OR 1.05 95% CI 1.00-1.09p= 0.04) for which PM 2.5 was primarily responsible (OR 1.06 95% CI 1.01-1.11p=0.03).The overall AQI, per 10 unit increase, was associated with increased events on lag days 2 and 3; these were significant for PM 2.5 , PM 10 , and sulfur dioxide.Effect modification was seen for AQI (continuous) for those with >1 event (Lag 2 OR 1.01, 95% CI 1.00-1.03P=0.05), aged 12-17 years (Lag 2: OR 1.02, 95%CI 1.00-1.03p=0.04), and Black children (Lag 2: OR 1.02, 95%CI 1.00-1.03p= 0.009, Lag 3: OR 1.01, 95%CI 1.00-1.03p=0.04,Lag 4: OR 1.02, 95%CI 1.00-1.03p=0.02).Conclusions: The overall air quality index is associated with ED visits and hospitalizations for asthma exacerbations in children in Allegheny County, PA, even for levels in the Good and Moderate ranges.Prospective studies evaluating the efficacy of AQI in preventing severe childhood asthma exacerbations are needed