1. Medical Faculty, Sofia University St. Kliment Ohridski, Kozyak 1 Str., 1407 Sofia, Bulgaria
2. Department of Gastroenterology, University Hospital Lozenetz, 1407 Sofia, Bulgaria
3. Department of General and Clinical Pathology, Medical University of Plovdiv, 15A Vasil Aprilov Bul. 4000 Plovdiv, Bulgaria
4. Medical Center Neovitro OOD, 20 Petko Yu. Todorov Bul., 1408 Sofia, Bulgaria
5. Department of Anesthesiology and Intensive Care, University Hospital Lozenetz, 1 Kozyak Str., 1407 Sofia, Bulgaria