• DezmanZachary D WZDWDepartment of Emergency Medicine, University of Maryland School of Medicine, Baltimore, Md; Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Md. Electronic address: zdezman@som.umaryla, Benoit Stryckman, Kori S Zachrison, Ryan M Conrad, David Marcozzi, Laura Pimentel, Margaret Samuels-Kalow, and Charles B Cairns.
• Department of Emergency Medicine, University of Maryland School of Medicine, Baltimore, Md; Department of Epidemiology and Public Health, University of Maryland School of Medicine, Baltimore, Md. Electronic address: zdezman@som.umaryland.edu.
• Am. J. Med. 2021 Oct 1; 134 (10): 1247-1251.

BackgroundMasking, which is known to decrease the transmission of respiratory viruses, was not widely practiced in the United States until the coronavirus disease 2019 (COVID-19) pandemic. This provides a natural experiment to determine whether the percentage of community masking was associated with decreases in emergency department (ED) visits due to non-COVID viral illnesses (NCVIs) and related respiratory conditions.MethodsIn this observational study of ED encounters in a 11-hospital system in Maryland during 2019-2020, year-on-year ratios for all complaints were calculated to account for "lockdowns" and the global drop in ED visits due to the pandemic. Encounters for specific complaints were identified using the International Classification of Diseases, version 10. Encounters with a positive COVID test were excluded. Linear regression was used to determine the association of publicly available masking data with ED visits for NCVI and exacerbations of asthma and chronic obstructive pulmonary disease (COPD), after adjusting for patient age, sex, and medical history.ResultsThere were 285,967 and 252,598 ED visits across the hospital system in 2019 and 2020, respectively. There was a trend toward an association between the year-on-year ratio for all ED visits and the Maryland stay-at-home order (parameter estimate = -0.0804, P = .10). A 10% percent increase in the prevalence of community masking was associated with a 17.0%, 8.8%, and 9.4% decrease in ED visits for NCVI and exacerbations of asthma exacerbations and chronic obstructive pulmonary disease, respectively (P < .001 for all).ConclusionsIncreasing the prevalence of masking is associated with a decrease in ED visits for viral illnesses and exacerbations of asthma and COPD. These findings may be valuable for future public health responses, particularly in future pandemics with respiratory transmission or in severe influenza seasons.Copyright © 2021 Elsevier Inc. All rights reserved.

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