Participants and definition
Patients were included from 18 European hospitals between March 22nd and June 3rd, 2020. The COVID-19 diagnosis was based on nasal swabs and virus identification with reverse transcriptase polymerase chain reaction (RT-PCR). Some patients benefited from serology (IgM and IgG). The patients had nasal swabs after presenting COVID-19 related symptoms. They were categorized in mild, moderate, severe and critical COVID-19 patients according to the COVID-19 Disease Severity Scoring of the World Health Organization.6 Mild patients consisted of home-managed patients without evidence of viral pneumonia or hypoxia. Moderate COVID-19 patients were defined as individuals with clinical findings of pneumonia (e.g. fever, cough, dyspnea, or tachypnea) but no sign of severe pneumonia (including SpO2≥90% on room air). The disease was categorized as severe when patients showed clinical findings of pneumonia associated with one of the following features: respiratory rate >30 breaths/min; severe respiratory distress; or SpO2<90% on room air. Subjects with critical disease had acute respiratory distress syndrome, sepsis or septic shock. These patients were admitted into intensive care units (ICU).