1. Centre for Infectious Diseases Control Netherlands, National Institute for Public Health and the Environment, PO Box 1, 3720 BA Bilthoven, the Netherlands
2. Division Veterinary Public Health, Institute for Risk Assessment Sciences, Utrecht University, PO Box 80175, 3508 TD Utrecht, the Netherlands
3. Department of Medical Microbiology and Infection Control, Free University Medical Centre, P.O. Box 7057, 1007 MB Amsterdam, the Netherlands
4. Department of Infectious Diseases and Immunology, Faculty of Veterinary Medicine, Utrecht University, PO Box 80163, 3508 TD Utrecht, the Netherlands
5. Central Veterinary Institute, PO Box 65, 8200 AB Lelystad, the Netherlands
6. Institute of Medical Microbiology, University of Göttingen, D-37075 Göttingen, Germany
7. Veterinary Laboratories Agency, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom