Severe asthma exacerbations associated with unconventional natural gas development activity in area of concentrated development.

Introduction: Residential proximity to unconventional natural gas development (UNGD) has been shown to be associated with asthma exacerbations, but there is limited evidence regarding whether exacerbations are associated with a particular distance or phase of well activity.

Objective: To study the impact of proximity to UNGD activity by well phase and buffer distance.

Methods: We included asthma patients 5-90 years old with a primary diagnosis of asthma and at least one order for medications prescribed for asthma residing in one of eight Southwestern Pennsylvania counties between 2011 and 2020. We matched events (severe exacerbation, emergency department visit, hospitalization) by age group, sex, and year to cohort members without an event of the same or greater severity. The primary exposure measure was an inverse distance-weighted index of UNGD activity up to 10 miles of a patient's residence. We fit a series of adjusted multilevel logistic regression models using tertiles of exposure activity by well phase and buffer distance.

Results: Our cohort consisted of 46,676 asthma patients. We found strong evidence for an increased risk specifically during the production phase for all buffer distances examined for all three event types, as based on consistent, statistically significantly elevated odds ratios. Elevations ranged from 2 to 8 times the baseline of no wells within 10 miles of the patient's residence.

Conclusion: This study provides evidence of increased risk of asthma events with the production phase. This should be considered in determining risk communication and assessment for these vulnerable populations, particularly during the production phase.