National decline in asthma exacerbations in United States during coronavirus disease 2019 pandemic.

Infection with coronavirus disease 2019 (COVID-19) has led to more than 4 million deaths worldwide, challenging our health care systems. At the same time, it has led to an increased use of nonpharmaceutical interventions (NPIs) to minimize disease spread. COVID-era NPIs such as physical distancing are associated with an unprecedented decrease of non–COVID-19 viral respiratory diseases.1, 2, 3

Viral respiratory infections are a common cause for asthma exacerbations that lead to emergency department (ED) and hospital use. There are now several reports suggesting the rates of asthma hospitalizations and ED visits have decreased during COVID-19.4, 5, 6 In this letter, we present the trends of ED and hospital use for asthma exacerbations in a sample of people from across the United States.

We used the Optum Labs Data Warehouse, a database of health care claims for more than 200 million privately insured and Medicare Advantage enrollees, to build the cohort, starting with all enrollees who had a diagnosis of asthma using diagnostic codes from 2007 to 2020. We defined ED and hospitalization events owing to asthma as those in which asthma was in the first diagnostic position for the claim or secondary position if the first diagnosis was respiratory infection. We reported asthma exacerbation rates per 100 people with asthma and analyzed them in 2007 to 2017, 2018 to March 2020, and March 2020 to December 2020 to correspond to 2007 release of National Heart, Lung, and Blood Institute updated asthma guideline, 2018 long acting β-agonist black box removal, and the March 2020 onset of the COVID-19 pandemic in the United States. We conducted a simple general linear model to compare the mean number of exacerbations between each time period and checked with Poisson regression using a spline for time and knots at guideline release, black box warning removal, and COVID-19 pandemic start.

We observed a general decline in the number of claims-computable asthma exacerbations (ED or hospitalization) from 2007 to 2020, with the largest decline occurring after March 2020. The mean exacerbation rates per 100 people with asthma were 0.92 (95% confidence interval [CI], 0.87-0.97), 0.62 (95% CI, 0.56-0.67), and 0.36 (95% CI, 0.27-0.44) for 2007 to 2017, 2018 to March 2020, and March 2020 to December 2020 (P < .001), respectively. Hospitalization rates per 100 people with asthma were 0.48 (95% CI, 0.22-0.74), 0.21 (95% CI, 0.19-0.22), and 0.12 (95% CI, 0.10-0.14) for 2007 to 2017, 2018 to March 2020, and March 2020 to December 2020 (P = .003), respectively. The results from the Poisson regression confirmed a statistically significant decline in asthma exacerbations (P < .001) after the COVID-19 pandemic onset, and the pseudo R-squared values for the regression of 0.85 suggested that the model matches the data well.

Our findings suggest that the decline in asthma exacerbations during the COVID-19 pandemic is not unique to specific hospital systems or geographic locations. A study in Philadelphia, Pennsylvania, found an 84% decrease in the emergency and inpatient settings, a study in Orange County, California, found a 78% decrease in hospitalization and 90% decrease in emergency visits, and a prospective study in multiple US locations found a 41% reduction in asthma exacerbations using composite, patient-informed definition.8, 9, 10

The significant decline in asthma exacerbations during the COVID-19 pandemic suggests, but does not prove, a causal relationship between physical distancing practices and reduced asthma exacerbations. Our results do not exclude the possibility that patients and families chose to avoid ED and hospital care for asthma during the COVID-19 pandemic. Nevertheless, Salciccioli et al describe a similar trend in a prospective study that captured both remote and in-person asthma exacerbations, making it less likely for the result to be influenced by health care system avoidance. Moreover, when they controlled for medication use and air quality values, the decrease in asthma exacerbation rates was still observed. Similarly, another study found that increased asthma medication adherence during the COVID-19 pandemic was not observed, at least in that population. Although we cannot exclude the possible influence of health care avoidance, air quality, or medication-taking behavior, these other studies suggest that these factors are unlikely to be primary drivers of the decrease in asthma exacerbations rates. Our data, finding this trend in a large sample in the United States, are consistent with previous studies revealing this trend and further extend previous observations by comparing rates to 13 previous years and by using participants who were not enrolled in research studies.

Our findings, together with other related studies, call for further research to better understand which NPIs may be most effective at reducing asthma exacerbations. Prospective trials of different NPI approaches (eg, wearing facemasks during fall-winter respiratory infection season) could isolate interventional effects and potentially provide new management options for our patients with asthma.