1. Institute of Infectious Diseases, University of Sassari, Sassari, Italy.
2. Epidemiology Unit, Department of Infectious Diseases, Istituto Superiore di Sanità, Rome, Italy.
3. Medical Center, Comunità di S. Patrignano, Rimini, Italy.
4. Clinic of Infectious Diseases, University of Bari, Bari, Italy.
5. Infectious Diseases Unit, Belcolle Hospital, ASL Viterbo, Italy.
6. Department of Medicine, University of Cagliari, Cagliari, Italy.
7. Infectious Diseases Unit, Vito Fazzi Hospital, Lecce, Italy.