1. Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, Zurich, Switzerland.
2. Department of Social and Preventive Medicine, University of Berne, Berne, Switzerland.
3. Division of Infectious Diseases, Kantonsspital St. Gallen, St. Gallen, Switzerland.
4. Division of Infectious Diseases, Hospital of Lugano, Lugano, Switzerland.
5. Division of Infectious Diseases, University Hospital Berne, Berne, Switzerland.
6. Division of Infectious Diseases, University Hospital Lausanne, Lausanne, Switzerland.
7. Division of Infectious Diseases, University Hospital Geneva, Geneva, Switzerland.