1. 1 Department of Infectious Diseases, Parasitology and Tropical Medicine , Medical University – Sofia , Bulgaria
2. 2 Infectious Disease Hospital “Prof. Ivan Kirov” – Sofia , Bulgaria
3. 3 National Laboratory “Influenza and ARD” , Department of Virology, National Centre of Infectious and Parasitic Diseases – Sofia , Bulgaria
4. 4 Multiprofile Hospital “Sv. Ivan Rilski” – Dupnitsa , Bulgaria
5. 5 Department of Medical Oncology , Medical University of Sofia, University Hospital “Tsaritsa Yoanna” – Sofia , Bulgaria