2 Department of Biometry, Epidemiology and Information Processing WHO-Collaborating Center for Research and Training for Health at the Human-Animal-Environment Interface University of Veterinary Medicine Hannover, Buenteweg 2, 30559 Hannover, Germany. Electronic address: lothar.kreienbrock@tiho-hannover.de.
3 National Institute for Public Health and the Environment (RIVM), P. O. Box 1, 3720 BA Bilthoven, The Netherlands. Electronic address: Engeline.van.Duijkeren@rivm.nl.
4 Institute of Microbiology and Epizootics, Centre of Infection Medicine, Department of Veterinary University, Freie Universität Berlin, Robert-von-Ostertag-Str. 7-13, 14163 Berlin, Germany. Electronic address: stefan.schwarz@fu-berlin.de.