1. Radboud University Medical CentreNijmegen, the Netherlands
2. Academic Medical CentreAmsterdam, the Netherlands
3. Erasmus Medical CentreRotterdam, the Netherlands
4. Leiden University Medical CentreLeiden, the Netherlands
5. University Medical CentreUtrecht, the Netherlands
6. University Medical Centre GroningenGroningen, the Netherlands
7. Maastricht University Medical CentreMaastricht, the Netherlands
8. VU University Medical CentreAmsterdam, the Netherlandsand
9. National Institute of Public Health and the EnvironmentBilthoven, the Netherlands