“…The following information was extracted from each study: first author, title, journal name, publication date, study periods, regions, sample size, demographic data (e.g., gender, age), chronic medical conditions (e.g., comorbidities, smoking history), clinical features (e.g., fever, headache), laboratory results (e.g., leukocytes, neutrophils), and radiographical features (e.g., ground-glass opacity, bilateral pulmonary infiltration). Three components, including selection, comparability, and exposure or outcome, were assessed for each study using the Newcastle-Ottawa Scale (Jaiswal et al, 2018;Xu and Lu, 2019). This consisted of eight items with a full score of nine stars (Stang, 2010).…”