1. Università Politecnica Marche, Virology Unit, Department of Biomedical Sciences and Public Health, Ancona, Italy
2. Azienda Ospedaliero-Universitaria Ospedali Riuniti di Ancona, Infectious Disease Unit, Department of Gastroenterology and Transplantation, Ancona, Italy
3. National Institute of Infectious Diseases L.Spallanzani, Rome, Italy
4. Istituto Superiore di Sanitá, Rome, Italy