1. Infectious Diseases Unit, Vita-Salute San Raffaele University, 20132 Milan, Italy
2. Infectious Diseases Unit, San Raffaele Scientific Institute, 20132 Milan, Italy
3. Infection Control, Chief Medical Office, San Raffaele Scientific Institute, 20132 Milan, Italy
4. Laboratory of Clinical Microbiology, Virology and Bioemergencies, L. Sacco University Hospital, 20122 Milan, Italy