A research letter published online in the Annals of the American Thoracic Society concluded that asthma may be an overestimated risk factor for hospitalisation due to coronavirus disease 2019 (COVID-19).
Richard Broadhurst, University of Colorado Anschutz Medical Campus, Aurora, Colorado, and colleagues compared the prevalence of asthma among patients hospitalised for COVID-19, as reported in 15 peer-reviewed studies, with that of the corresponding population’s asthma prevalence. They also correlated the study’s asthma prevalence with the 4-year average asthma prevalence in influenza hospitalisations in the United States. In addition, they analysed the medical records of 436 patients with COVID-19 admitted to the University of Colorado Hospital to evaluate the likelihood of intubation in patients with asthma compared to patients without asthma.
“According to the Centers for Disease Control (CDC), individuals with asthma are also at higher risk for hospitalisation and other severe outcomes from COVID-19; however, the low numbers of asthmatics among hospitalised patients across many international available studies challenges this assumption,” the authors stated.
The researchers performed a focused review of English-language scientific literature in order to identify studies reporting asthma prevalence among patients hospitalised for COVID-19 infection. Three independent reviewers agreed on 15 studies to include in the analysis. Using local data from hospitalised COVID-19 patients, they performed a statistical analysis to determine the relationship between asthma status and intubation, once they took into account patients’ age, gender, and body mass index (BMI).
“The proportion of asthmatics among hospitalised patients with COVID-19 is relatively similar to that of each study site’s population asthma prevalence,” the authors wrote. “This finding is in stark contrast to influenza, in which patients with asthma make up more than 20% of those hospitalised in the United States.”
The researchers noted that 24.1% of people hospitalised with influenza had asthma during the 2019-2020 influenza season, which is slightly higher than the 4-year 21% average from 2016-2020. They added that this is considerably higher than the pooled prevalence estimate across the 15 COVID-19 studies (6.8% (95% CI: [3.7, 10.7]).
“Using data from our hospital, we observed that among COVID-19 patients, those with asthma (12% prevalence), identified using ICD 10 code – J45, do not seem to be more likely than non-asthmatics to be intubated (odds ratio: 0.69 (95% CI: [0.33, 1.45]), after adjusting for age, sex, and BMI,” the authors stated.
The researchers theorised that the corticosteroid inhalers many people with asthma use may decrease ACE2 expression, making it more difficult for coronaviruses to enter their airways. “Additionally, asthma patients in general, and particularly those with a predominantly allergic phenotype, may have significantly lower expression of ACE2,” they said.
“The contribution of ACE2 receptor expression levels to overall COVID-19 susceptibility and disease severity is still unclear, it is certainly worth further investigation,” the authors wrote.
“While there is variable asthma prevalence among COVID-19 published studies, it appears similar to population prevalence, and certainly much lower than what would be expected during seasonal flu. The results of this study suggest that asthma does not appear to be a significant risk factor for developing severe COVID-19 requiring hospitalisation or intubation,” the authors concluded.