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B1663
Title: Acute exposure to ambient particulate matter and pulmonary exacerbations: A case-crossover simulation study Authors:  Stephen Colegate - Cincinnati Children's Hospital Medical Center (United States) [presenting]
Cole Brokamp - University of Cincinnati (United States)
Rhonda Szczesniak - Cincinnati Children Hospital Medical Center (United States)
Marepalli Rao - University of Cincinnati (United States)
Abstract: Cystic fibrosis (CF) is an autosomal recessive disorder characterized by chronic lung infections and recurrent respiratory symptoms called pulmonary exacerbations (PEx). Individual PEx symptoms may substantially vary according to changes in lung function, nutrition and other clinical factors, and there is no consensus on timely treatment initiation. The Early Intervention in Cystic Fibrosis Exacerbation Study (eICE) determined whether early treatment of PEx events with home monitoring devices is beneficial. We implemented a case-crossover design to evaluate whether PEx events were associated with daily ambient fine particulate matter (PM2.5). The results indicate an increase in PEx cases with higher PM2.5, although this association depends on the selection of a suitable washout period between two consecutive PEx events. We simulate data based on our applied eICE study to estimate the bias and precision of the odds ratio (OR) estimate for various washout periods. Our case-crossover simulation shows how a short washout period introduces bias while also demonstrating how a conservative washout period affects the precision of the OR estimate. We strongly recommend a washout period of 14 days for the case-crossover design modeling PEx outcomes. The simulation study illustrates a broader implication for the development and application of the case-crossover design.