1. 1Centre for Prevention and Health Services Research, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
2. 2Centre for Infectious Disease Control, National Institute for Public Health and the Environment, P.O. Box 1, 3720 BA Bilthoven, The Netherlands
3. 3Department of Public Health, Erasmus Medical Centre, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands
4. 4Institute for Risk Assessment Sciences, Utrecht University, P.O. Box 80178, Utrecht, The Netherlands