## 2 Materials and Methods  
We conducted this case-control study by extracting data from a consecutive registry of adult patients with evidence of SARS-CoV-2 infection admitted to the ED of our hospital between March 2020 and January 2021. The Agostino Gemelli University Hospital, one of the largest in Rome (Italy), is a tertiary center with > 80,000 visits to the ED every year. The registry was created by consulting the electronic health records of two different health information systems, the former specific for ED and the latter for hospitalized patients.  
The inclusion criteria were: age \(\geq\) 18 years, ED admission for symptoms compatible with COVID-19, and evidence of SARS-CoV-2 infection obtained by a molecular nasopharyngeal swab performed after hospital arrival.  
We searched the registry for all individuals with asthma, who, as for all other comorbidities, were identified on the basis of the International Classification of Diseases, Tenth Revision (ICD-10) codes recorded in the medical records. For each COVID-19 asthma patient, we identified one COVID-19 non-asthma patient comparator, matched by age, sex, race, and enrollment period (within 14 days).We collected the following data from all individuals: demographic variables, smoking habits, body mass index (BMI), main comorbidities (diabetes mellitus, arterial hypertension, significant cardiopathies such as chronic heart failure and/or ischemic heart disease, and COPD), ongoing treatment with inhaled or oral corticosteroids (ICS or OCS), PaO\({}_{2}\) ratio/FiO\({}_{2}\) upon arrival, C-reactive protein (CRP), and AEC. As widely adopted, multimorbidity was defined as the presence in the same individual of \(\geq\)2 chronic diseases [20]. In addition, we registered the principal pharmacological treatments for COVID-19 administered to hospitalized patients.  
Incomplete data and unavailability of the molecular swab report for SARS-CoV-2 made after arrival in our ED were exclusion criteria. The end-points explored were: hospitalization, intensive care unit (ICU) admission, pharmacological treatment for COVID-19, need for high-flow nasal cannula oxygenation (HFNCO), non-invasive ventilation (NIV), continuous positive airway pressure (CPAP), mechanical ventilation (MV), death, and length of stay (LOS). LOS was calculated since arrival at the ED until hospital discharge/demise. We classified as critical COVID-19 all individuals with any of the following: need for ventilatory support through CPAP and/or NIV and/or MV and/or ICU admission and/or death related to COVID-19. In addition, we consulted the electronic health records of our hospital to assess whether individuals included in the present study and discharged to home after the first contact had returned to the ED within 1 month of enrollment.  
Primary outcomes were the proportion of patients requiring hospitalization and those with critical COVID-19. Need for HFNCO, in-hospital mortality, and LOS were also compared between the two groups. Finally, in patients with asthma, we assessed the relationship between AEC and the primary outcomes.  
We reported the data as percentages for categorical variables and as mean (standard deviation) for continuous variables. We compared categorical variables by \(\chi\)2 test or Fisher exact test, and continuous variables by independent t-test or Mann-Whitney U test. We used multivariate logistic regression analysis to assess whether asthma was independently associated with hospitalization and critical COVID-19. All variables showing \(p\) value \(\leq\) 0.1 during univariate analysis were included in the multivariate model. We performed the statistical analysis using IBM SPSS 26 software (IBM Corp., Armonk, NY, USA); \(p\)-values \(<\) 0.05 were considered statistically significant.  
The present study was approved by the Ethics Committee of the Fondazione Policlinico Universitario Agostino Gemelli--IRCCS, Rome, Italy (approval number 0014840/22).