1. National Institute for Public Health and the Environment (RIVM), Bilthoven, the NetherlandsDutch Association for Public Health Services, Utrecht, the Netherlands
2. University Medical Centre, St. Radboud, Nijmegen, the Netherlands
3. National Institute for Public Health and the Environment (RIVM), Bilthoven, the NetherlandsEuropean Centre for Disease Prevention and Control, Stockholm, Sweden
4. Health Protection Agency, London, UK
5. National Institute for Public Health and the Environment (RIVM), Bilthoven, the Netherlands