1. Clinical Immunology Laboratory, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
2. Laboratory of Microbiology and Virology, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
3. Department of Pediatrics, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
4. Department of Gastroenterology, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
5. Department of Hemodyalisis, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
6. Intensive Care Unit, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.
7. Department of Surgery, University Hospital “Lozenetz,” Sofia University “St. Kliment Ohridski,” Sofia, Bulgaria.