Institute for Integrative Biology, ETH Zurich, Switzerland.|Division of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, Connecticut, United States of America.|Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, University of Zurich, Switzerland & Institute of Medical Virology, Swiss National Center for Retroviruses, University of Zurich, Zurich, Switzerland.|Institute for Integrative Biology, ETH Zurich, Switzerland.