1. a Centre for Infectious Disease Control , National Institute for Public Health and the Environment (RIVM) , Bilthoven , The Netherlands
2. b Municipal Health Service , The Hague , The Netherlands
3. c Municipal Public Health Service , Rotterdam-Rijnmond , The Netherlands
4. d European Centre for Disease Prevention and Control (ECDC) , Stockholm , Sweden
5. e Center for Infection and Immunity Amsterdam, Academic Medical Centre , University of Amsterdam , Amsterdam , The Netherlands
6. f Health Service , Amsterdam , The Netherlands