1. Departments of Medical Microbiology1 and
2. Pediatrics,2 University Hospital Nijmegen, 6500 HB Nijmegen,
3. Inspectorate for Health Protection, Food Inspection Service, 7200 GN Zutphen,3
4. Veterinary Public Health Inspectorate, 6800 DR Arnhem,4 and
5. Department of the Science of Food of Animal Origin, Utrecht University, 3508 TD Utrecht,5 The Netherlands