1 Department of Public and Global Health, Division of Infectious Diseases, World Health Organization Collaborating Centre for Traveller's Health, Epidemiology, Biostatistics and Prevention Institute, University of Zurich, Zurich, Switzerland.
2 Division of Epidemiology, Human Genetics and Environmental Sciences, University of Texas School of Public Health, Houston, TX, USA.
3 Department of Global Health, Boston University School of Public Health, Boston, MA, USA.
4 Section of Infectious Diseases, Department of Medicine, Boston Medical Center, Boston, MA, USA.