1. Division of Clinical Epidemiology, Department of Clinical Research, University Hospital Basel , Basel , Switzerland
2. Division of Clinical Epidemiology, Department of Clinical Research, University of Basel , Basel , Switzerland
3. Department of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich , Zurich , Switzerland
4. Institute of Social and Preventive Medicine, University of Bern , Bern , Switzerland
5. Institute of Medical Virology, University of Zurich , Zurich , Switzerland
6. SolidarMed, Partnerships for Health , Maseru , Lesotho
7. Division of Infectious Diseases and Hospital Epidemiology, University Hospital Basel , Basel , Switzerland