1. MRC Health Service Research Collaboration, Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Rd, Bristol BS8 2PR and Department
of Public Health Sciences, King's College London, London, UK
2. Department of Public Health Sciences, King's College London, London, UK
3. Department of Sexual Health, King's NHS Healthcare Trust, London, UK
4. Department of Virology, Dulwich PHLS, King's NHS Healthcare Trust, London, UK
5. Young People's Health Project, Lewisham, London, UK
6. Health First, Lambeth, Southwark and Lewisham Health Promotion, London, UK
7. Blackliners, London, UK
8. MRC Health Service Research Collaboration, Department of Social Medicine, University of Bristol, Canynge Hall, Whiteladies Rd,
Bristol BS8 2PR and Department of Public Health Sciences, King's College London, London, UK