1. University Medical Center Groningen, Groningen, the Netherlands;
2. University of Linz, Linz, Austria;
3. Vrije Universiteit Brussel, Brussels, Belgium;
4. University Hospital for Infectious Diseases, Zagreb, Croatia;
5. Charles University, Prague, Czech Republic;
6. Statens Serum Institut, Copenhagen, Denmark;
7. Health Protection Surveillance Centre, Dublin, Ireland;
8. Consorzio Mario Negri Sud, Chieti, Italy;
9. Ha'Emek Medical Center, Afula, Israel;
10. Institute of Hygiene, Vilnius, Lithuania;
11. Directorate of Health, Luxembourg, Luxembourg;
12. St Luke's Hospital, G'Mangia, Malta;
13. National Institute of Public Health, Warsaw, Poland;
14. Max Planck Institute for Demographic Research, Rostock, Germany;
15. Comenius University, Bratislava, Slovakia;
16. University Medical Centre, Ljubljana, Slovenia;
17. Instituto de Salud Carlos III, Madrid, Spain;
18. Karolinska Institutet, Göteborg, Sweden;
19. Nottingham City Hospital, Nottingham, United Kingdom