1. Department Viroscience, Erasmus University Medical Center, Rotterdam, the Netherlands
2. Centre for Infectious Disease Control, National Institute for Public Health and the Environment, Bilthoven, the Netherlands
3. General practitioner participating in the Primary Care Database sentinel surveillance coordinated by NIVEL Netherlands institute for health services research, Utrecht, the Netherlands
4. Coordinator NIVEL Primary Care Database sentinel surveillance, NIVEL Netherlands institute for health services research, Utrecht, the Netherlands
5. Municipal Health Services ‘Gooi en Vechtstreek’, Bussum, the Netherlands
6. Central Bacteriology and Serology Laboratory, Tergooi Hospitals, Hilversum, the Netherlands