Study settings and definitions:
Severe and critical patients with COVID-19 were defined following Ministry of Health, General Directorate of Public Health COVID-19 (SARS-CoV-2 Infection) Adult Patient Treatment Scientific Advisory Board Study guidelines for diagnosis and treatment (version October 9, 2020). In this guideline, severe patients who should be hospitalized with at least one of the following clinical features in addition to fever, myalgia, cough, sore throat are specified; respiratory rate exceeding 30 breaths/minute at rest, oxygen saturation 90% without oxygen support, and bilateral pneumonia on chest CT.
Corticosteroid treatment was ordered by the attending physician. Low-dose steroid therapy (dexamethasone 8 mg ) was applied to all patients from the first day to discharge. High-dose, short-term corticosteroid therapy was defined as ≥250 mg of methylprednisolone intravenously for three days. Early use of high-dose corticosteroid was defined as corticosteroid therapy within 7 days after hospital admission. Methylprednisolone 40-80mg/day was continued throughout the hospitalization to the patients receive high-dose steroid.