Department of General and Clinical Pathology;
Medical University;
University Hospital"St George";
Plovdiv 6000;
Bulgari;
Department of Thoraco-abdominal Surgery;
Medical University;
Plovdiv 6000;
Bulgaria;
University Clinic for Digestive Surgery;
Medical Faculty;
Skopje 1000;
Macedonia;
Department of Clinical Immunology;
University Hospital Lozenetz;
Sofia 1407;
Bulgaria;
Medical Faculty;
Sofia University St.Kliment Ohridski;
Sofia 1407;
Bulgaria;
COVID-19; SARS-CoV-2; Surgery; Surgery complications; Mortality rate; Acute respiratory distress syndrome; Thrombosis;