1. Unit of Hygiene, Epidemiology and Public Health; University of Brescia; Brescia Italy
2. Infectious Diseases Service; Department of Medicine; University Hospital and University of Lausanne; Lausanne Switzerland
3. Department of Infectious Diseases; University of Goteborg; Goteborg Sweden
4. Division of Clinical Pathology; University Hospitals; Geneva Switzerland
5. Division of Gastroenterology and Hepatology; University Hospitals; Geneva Switzerland
6. Clinic of Gastroenterology; Department of Medicine; University of Verona; Verona Italy