A recent review of research suggests that the proportion of all hospitalized COVID-19 patients who also have asthma is similar to the prevalence of asthma in the general population.
In their latest advice, the Centers for Disease Control and Prevention (CDC) warns that people with moderate to severe asthma may be at increased risk of developing severe COVID-19.
However, a review of the research conducted by scientists at the University of Colorado in Denver found no evidence of a higher prevalence of asthma among hospitalized COVID-19 patients compared to the prevalence of the disease in the general population.
Furthermore, they found that hospitalized COVID-19 patients who had asthma were no more likely to be intubated than other patients.
In a research letter appearing in the Annals of the American Thoracic Society , the authors report:
“The CDC places people with asthma at higher risk of COVID-related hospitalization,” says lead author Dr. Fernando Holguin. “However, many international studies show a low number of asthmatics among hospitalized COVID-19 patients. These findings challenge the assumption about asthma as a risk factor.”
In a research letter appearing in the Annals of the American Thoracic Society , the authors report:
"Despite initial concerns about disproportionately high morbidity and mortality for people with asthma, the data presented here and elsewhere show minimal evidence of a clinically significant relationship."
Prevalence comparison
For their analysis, the researchers identified 15 studies published in English before May 7, 2020, that reported on the prevalence of asthma among hospitalized COVID-19 patients. The studies were conducted in Brazil, China, South Korea, the United Kingdom, and the United States.
When they compared these figures with the prevalence of asthma in each population, the figures were very similar.
Although the prevalence of asthma among hospitalized patients with COVID-19 varied widely from study to study, the overall prevalence was around 7%.
Conversely, the authors found that people with asthma accounted for more than 20% of all those hospitalized with influenza in the US.
Finally, they analyzed whether patients admitted to the University of Colorado Hospital with COVID-19 were more likely to be intubated if they had asthma. After adjusting for patients' age, sex, and body mass index (BMI), they found no evidence that this was the case.
In conclusion, they write:
“While there is a variable prevalence of asthma among published COVID-19 studies, it appears similar to the prevalence in the general population and certainly much lower than would be expected during seasonal influenza. The results of this study suggest that asthma does not appear to be a significant risk factor for developing severe COVID-19 requiring hospitalization or intubation.”
ACE2 receptors
The authors speculate that people with asthma who use inhaled corticosteroids may have fewer ACE2 receptors in the lining of their respiratory tract. These are the receptors the virus uses to enter its host cells.
They add that people with asthma in general, and allergic asthma in particular, may have fewer ACE2 receptors.
However, they write that the effect of ACE2 receptor numbers on a person's risk of COVID-19 and disease severity remains unclear and warrants further investigation.
They also acknowledge that their study had some limitations.
For example, the prevalence of asthma among hospitalized COVID-19 patients varied widely across studies, suggesting a lack of consistency in the reporting of comorbid conditions. Furthermore, some studies did not describe how researchers collected data on asthma diagnoses.
The authors also note that their sample size may not be large enough to draw definitive conclusions. They call for more research on the risk of severe COVID-19 for people with asthma.