Institute of Social and Preventive Medicine, University of Bern, Switzerland.|Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.|Centre for Infectious Disease Epidemiology and Research, University of Cape Town, South Africa.|Institute of Social and Preventive Medicine, University of Bern, Switzerland.|Institute of Social and Preventive Medicine, University of Bern, Switzerland.|Institute of Social and Preventive Medicine, University of Bern, Switzerland.|Institute of Social and Preventive Medicine, University of Bern, Switzerland.|Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Zurich, Switzerland.