1. Faculty of Medicine, University of Belgrade, Dr Subotica Starijeg 8, 11000 Belgrade, Serbia
2. Clinic for Gastroenterology and Hepatology, University Clinical Center of Serbia, Koste Todorovica No 2, 11000 Belgrade, Serbia
3. Department of Internal Medicine, General Hospital Novi Pazar, Generala Zivkovica 1, 36300 Novi Pazar, Serbia
4. Department of Internal Medicine, General Hospital Jagodina, Karadjordjeva 4, 35000 Jagodina, Serbia
5. Faculty of Dental Medicine, University of Belgrade, Rankeova 4, 11000 Belgrade, Serbia
6. Department of Gastroenterology, Clinical and Hospital Center “Dr Dragisa Misovic–Dedinje”, Heroja Milana Tepica 1, 11020 Belgrade, Serbia
7. Clinic for Pulmology, University Clinical Center of Serbia, Dr Koste Todorovica No 6, 11000 Belgrade, Serbia