1. Department of Infectious Diseases, Institute of Infectious Diseases and Public Health, University of Ancona, I-60121 Ancona,1
2. Department of Hygiene, Institute of Infectious Diseases and Public Health, University of Ancona, I-60100 Ancona,2 and
3. Department of Infectious Diseases, San Salvatore Hospital, I-60121 Pesaro,3 Italy