A recent review of research suggests that the proportion of all patients hospitalized with COVID-19 who also have asthma is similar to the prevalence of asthma in the wider population.

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Research indicates that people with asthma may not be more at risk of severe COVID-19.

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In their latest advice, the Centers for Disease Control and Prevention (CDC) warn that people with moderate-to-severe asthma may be at greater risk of developing severe COVID-19.

However, a review of research by scientists at the University of Colorado in Denver has found no evidence of an increased prevalence of asthma among patients hospitalized with COVID-19 compared with the condition’s prevalence in the wider population.

In addition, they found that patients hospitalized with COVID-19 who had asthma were no more likely to be intubated than other patients.

“The CDC [place] people with asthma at higher risk [of] COVID-related hospitalization,” says senior author Dr. Fernando Holguin. “However, many international studies show low numbers of [asthmatic people] among hospitalized COVID-19 patients. These findings challenge the assumption about asthma as a risk factor.”

In a research letter that appears in the Annals of the American Thoracic Society, the authors report:

“Despite early concern about disproportionately high morbidity and mortality for those with asthma, data presented here and elsewhere show minimal evidence of a clinically significant relationship.”

For their analysis, the researchers identified 15 studies published in English before May 7, 2020, that reported on asthma prevalence among patients hospitalized with COVID-19. The studies took place in Brazil, China, the Republic of Korea, the United Kingdom, and the United States.

When they compared these figures with the prevalence of asthma in each population, the numbers were broadly similar.

Although the prevalence of asthma among hospitalized COVID-19 patients varied widely from study to study, the overall prevalence was around 7%.

By contrast, the authors found that people with asthma accounted for more than 20% of all those hospitalized with influenza in the U.S.

Finally, they looked at whether or not patients admitted to the University of Colorado Hospital with COVID-19 were more likely to be intubated if they had asthma. After adjusting for the patients’ age, sex, and body mass index (BMI), they found no evidence that this was the case.

In conclusion, they write:

“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 hospitalization or intubation.”

The authors speculate that people with asthma who use inhaled corticosteroids may have fewer ACE2 receptors in the lining of their respiratory tract as a result. These are the receptors that the virus uses to enter its host’s 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 merits further investigation.

They also acknowledge that their study had some limitations.

For example, the prevalence of asthma among patients hospitalized with COVID-19 varied widely between studies, which suggests that there was a lack of consistency in reporting comorbid conditions. Also, some studies did not describe how the researchers gathered 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 into the risk of severe COVID-19 for people with asthma.

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