Int J Epidemiol 2014 Jun 22;43(3):887-96. Epub 2014 Jan 22.
Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland, Department of Infectious Diseases, Bern University Hospital and University of Bern, Bern, Switzerland, Institute of Medical Virology, University of Zurich, Zurich, Switzerland, Laboratory of Virology, University Hospital Geneva, Geneva, Switzerland, Division of Immunology and Allergy, University Hospital Lausanne, University of Lausanne, Lausanne, Switzerland, Department Biomedicine, University of Basel, Basel, Switzerland, Division of Infectious Diseases, Geneva University Hospital, Geneva, Division of Immunology, University Hospital Lausanne, Lausanne, Switzerland, Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel, Basel, Division of Infectious Diseases, Cantonal Hospital St Gallen, St Gallen, Switzerland and Division of Infectious Diseases, Regional Hospital Lugano, Lugano, Switzerland.