Introduction:  
The role of comorbid conditions in susceptibility to SARS-CoV-2 infection and the severity of its associated disease, COVID-19, has been an area of ongoing investigation since the start of the pandemic. It is well known that viral infections are a common cause for asthma exacerbations requiring hospitalization, and previous studies have shown associations between infections with common respiratory viruses as well as coronaviruses (OC43 and 229E) and asthma exacerbations in both pediatric and adult patients.1,2 Given that SARS-CoV-2 is a respiratory illness which causes viral pneumonia as a primary manifestation, experts initially suspected the virus might exert a similar effect and that those with underlying respiratory illnesses, such as asthma, might be at higher risk for poor outcomes from infection with the virus. As such, at the onset of the pandemic, both the Centers for Disease Control and Prevention (CDC) and World Health Organization (WHO) advised that patients with asthma may be at greater risk for severe illness.
Despite this initial hypothesis, the published data regarding the effect of comorbid asthma on clinical outcomes have been discrepant. Although findings vary regionally, asthma prevalence in patients hospitalized with COVID-19 appears to be lower than in the general populations of Brazil, China, Italy, Russia, Saudi Arabia and Sweden.3 In addition, several systematic reviews have reported no increased risk for COVID-19 infection and hospitalization in asthmatics.4-6 Conversely, in cohorts of COVID-19 patients within the United States, recent studies have revealed the asthma prevalence to be up to 11% greater than the national average,7 while also suggesting that asthma may be a risk factor for poor clinical outcomes. A retrospective, single-center review of patients who tested positive for SARS-CoV-2 in Washington, D.C., documented an increased risk for intubation in patients with asthma as compared to those without asthma.8 However, in a separate study from Denver, Colorado, there was no association between asthma and risk for intubation.9 More recently, a large cohort study from the United Kingdom showed asthmatics aged 16-49 were more likely to receive critical care.10 However, the authors note that asthmatics did not necessarily have more clinically severe disease, so the increased rates of critical care for these patients may have been due to other factors, such as provider preference for closer monitoring given underlying respiratory disease. This same study also showed increased mortality for severe asthmatics, although the definition of severe asthma was based on patient self-reports of maintenance medications taken in the two weeks prior to hospital admission.
Previous studies have also suggested that patients with a non-allergic asthma phenotype may be at increased risk for severe COVID-19 disease when compared to patients with allergic asthma.11,12The angiotensin converting enzyme 2 (ACE-2) receptor has previously been identified as the cellular receptor for SARS-CoV-2 and reduced ACE-2 expression has been reported in patients with allergic asthma, which would support a possible protective effect of an allergic asthma phenotype on COVID-19 disease severity.13 A single-center retrospective analysis of patients presenting to the ED at a tertiary academic center in the Bronx, New York, supported the role of pre-existing eosinophilia (AEC ≥150 cells/μL, a biomarker of allergic inflammation) as a protective characteristic against hospitalization with COVID-19. 14 Taken together, these findings suggest the nuanced role of asthma phenotypes in predicting clinical outcomes of COVID-19. Therefore, the aim of this study was to evaluate all patients who tested positive for SARS-CoV-2 to determine the impact of asthma and asthma phenotypes on disease severity and outcomes in COVID-19 patients.