1. University of Bern; Institute of Social and Preventive Medicine (ISPM); Finkenhubelweg 11 Bern Switzerland CH-3012
2. University of Tartu; Department of Public Health; Tartu Estonia
3. University of Amsterdam; Department of General Practice and Family Medicine; Amsterdam Netherlands
4. Imperial College London; Department of Infectious Disease Epidemiology; London UK
5. Department of Public Health Programmes; Skovlyvej 1, 8930 Randers Denmark
6. Rotterdam-Rijnmond Public Health Service; Department of Infectious Disease Control; PO Box 70032 3000 LP Rotterdam Rotterdam Netherlands