1. Epidemiology and Surveillance Unit
2. Laboratory for Infectious Diseases and Perinatal Screening Centre for Infectious Disease Control; National Institute for Public Health and the Environment; Bilthoven
3. Department of Nursing Home Medicine and Department of Public and Occupational Health; VU University Medical Center; EMGO Institute for Health and Care Research; Amsterdam
4. Julius Centre; University Medical Centre Utrecht; Utrecht
5. Department of Public Health and Elderly Care Medicine; Leiden University Medical Centre; Leiden; the Netherlands