1 University of Zürich Centre for Travel Medicine, WHO Collaborating Centre for Travellers' Health, Epidemiology, Biostatistics and Prevention Institute, 8001 Zürich, Switzerland. Electronic address: pat@ifspm.uzh.ch.
2 EuroTravNet Statistician, Victoria, BC, Canada.
3 University Hospital Institute for Infectious and Tropical Diseases, Aix-Marseille University, Marseille, France.
4 Centre for Tropical Medicine and Travel Medicine, Department of Infectious Diseases, Academic Medical Centre, University of Amsterdam, Amsterdam, Netherlands.