1. Department of Medical Microbiology, Medical Faculty, Medical University Sofia, Sofia, Bulgaria.
2. MICOER Institute, Munich, Germany.
3. Medical Institute, Ministry of the Interior, Sofia, Bulgaria.
4. Second Multiprofile Active Treatment Hospital, Sofia, Bulgaria.
5. Emergency Medical Institute “Pirogov,” Sofia, Bulgaria.
6. Varna University Hospital, Varna, Bulgaria.
7. Department of Microbiology, Medical University, Pleven, Bulgaria.