Introduction
The current coronavirus-induced disease 2019 (COVID-19) pandemic due to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is a major burden for the global healthcare infrastructure. Several comorbidities such as diabetes, hypertension, coronary heart disease, obesity and metabolic syndrome confer an increased the risk for SARS-CoV-2 infection and/or severe COVID-19, including COVID-19-associated mortality . In contrast to seasonal influenza, an early cohort reported that the prevalence of asthma among COVID-19 patients in the Tongji Hospital (Wuhan) was 0.9%, lower than that in the adult population of Wuhan (6.4%) . We previously published on the global epidemiology of asthma among COVID-19 patients and found striking geographic differences defining high (eg USA, UK, Ireland and Australia) and low (eg China, Italy, Spain, Israel, Mexico, Brazil, Saudi Arabia, India) asthma COVID-19 zones . However, why these differences were observed was unclear.
Individuals with asthma are more susceptible to respiratory viral infections and the majority of acute asthma exacerbations are preceded by a common cold, which is attributed to rhinoviruses, influenza and respiratory syncytial virus (RSV) among other viruses . Furthermore, asthma has been consistently recognized as a major risk factor for influenza-associated hospitalization across several seasons reviewed in . In regards to COVID-19 infections, data indicate that SARS-CoV-2 infection is not associated with acute asthma exacerbations but the relationship between asthma and severe COVID-19 outcomes is less clear. Early onset asthma is associated with a lower risk of SARS-CoV-2 positive PCR test . Some studies suggest that non-allergic asthma is associated with a greater risk for severe COVID-19 as compared to individuals with allergic/type 2 asthma . Indeed, there is evidence that type 2 mediator IL-13 inhibits SARS-CoV-2 infection of bronchial epithelium and that asthma medication such as inhaled corticosteroids protect from worsening COVID-19 symptoms. Inhaled corticosteroids presumably reduce the expression of angiotensin converting enzyme-2 (ACE-2) and transmembrane protease serine in the lung . Currently, there is no indication that children with asthma are at higher risk for (severe) COVID-19 than children without asthma .
There is little information on the interrelationship between COVID-19 and chronic inflammatory airway disorders studied by international sites using validated and unified criteria. Such reports often correct for age and sex but very rarely adjust for existing comorbidities, which can vary greatly throughout the world. In this context, the objective of our study was to compare asthma prevalence among hospitalized COVID-19 patients in major global hubs across continents as well as associated clinical and laboratory features.