1. National Reference Confirmatory Laboratory of HIV, National Center of Infectious and Parasitic Diseases, Sofia, Bulgaria
2. National Reference Laboratory of Hepatitis, National Center of Infectious and Parasitic Diseases, Sofia, Bulgaria
3. Specialized Hospital for Active Treatment of Infectious and Parasitic Diseases, Sofia, Bulgaria
4. Department of Infectious Diseases, Medical University, Plovdiv, Bulgaria
5. Department of Infectious Diseases, Medical University, Pleven, Bulgaria
6. Clinic of Infectious Diseases, University Hospital, Stara Zagora, Bulgaria
7. National Reference Laboratory of Immunology, National Center of Infectious and Parasitic Diseases, Sofia, Bulgaria