Study design and participants

Patients with moderate and severe COVID-19 who were admitted to Imam Khomeini Hospital Complex during 20 February to 29 March 2020 were enrolled in this prospective cohort study. The hospital is one of the major hospitals for admission and care of patients with COVID-19 in Tehran, capital of Iran. According to the national committee of COVID-19, the admission indications were the presence of one or more of the subsequent conditions: (1) peripheral oxygen saturation (SpO2) less than 93% in ambient air (2) respiratory rate more than 30 breath per minute (3) lung infiltration highly suspicious for COVID-19 in chest imaging. Discharge criteria included all of the following: (1) improvement in clinical signs and symptoms based on decision making of physician (2) afebrile status for 72 h without antipyretics (3) SpO2 more than 93% in ambient air without supplemental oxygen.

According to the disease severity and WHO definitions [6], the patients were categorized to moderate or severe group. Patients in the moderate group had primary symptoms of pneumonia (dyspnea, cough and fever) and SpO2 ≥ 90% in ambient air and patients in the severe group had profound pneumonia and SpO2 < 90%.

The sampling for diagnosis of infection was performed according to the WHO interim guidance [7]. The diagnosis was according to positive reverse transcriptase- polymerase chain reaction (RT-PCR) of nasopharyngeal secretions (197 patients) or clinical data plus chest CT scan findings that were highly suggestive for COVID-19 (16 patients).

Ethics Committee of Tehran University of Medical Sciences approved the study (approval ID: IR.TUMS.VCR.REC.1398.1058). Written informed consents were obtained from the patients or one of the first-degree family members if patient was unconscious. The study protocol was also registered as IRCT20100228003449N30.