antibiotic agent; anticoagulant agent; antivirus agent; endogenous compound; glucocorticoid; hydroxychloroquine; immunomodulating agent; interleukin 6 receptor; adult; artificial ventilation; body mass; capillary; capillary density; cohort analysis; comorbidity; conference abstract; continuous positive airway pressure; controlled study; coronavirus disease 2019; demography; drug therapy; female; human; human cell; imaging software; Italy; laser; major clinical study; male; optical coherence tomography angiography; oxygen therapy; rheumatologist; risk factor; scintigraphy; skin; survivor; thrombosis; Venturi mask; video microscopy; videocapillaroscopy