1. Microbiology and Virology Unit, University Hospital Città della Salute e della Scienza di Torino, 10126 Turin, Italy
2. Department of Public Health and Paediatrics, University of Torino, 10126 Turin, Italy
3. Department of Medical Sciences, Infectious Diseases, University of Turin, 10126 Turin, Italy
4. Unit of Infectious Diseases, Cardinal Massaia, 14100 Asti, Italy