1 COVID-19 Unit, GNDA "Agia Varvara" Hospital, Athens, Greece.
2 2nd Respiratory Medicine Department, General University Hospital "Attikon", Medical School, National and Kapodistrian University of Athens, Athens, Greece.
3 Department of Respiratory Medicine, General Hospital G. Papanikolaou, Pulmonary Department of Aristotle University of Thessaloniki, Thessaloniki, Greece.
4 Respiratory Medicine Department, University of Ioannina, Faculty of Medicine, Ioannina, Greece.
5 4th Respiratory Medicine Department, Sotiria Hospital, Athens, Greece.
6 4th Internal Medicine Department, General University Hospital "Attikon", Medical School, National and Kapodistrian University of Athens, Athens, Greece.