1. Department of Sexually Transmitted Diseases, Royal Free and University College Medical School, Mortimer Market Centre, off Capper Street, London
WC1E 6AU, UK
2. Department of Infectious Diseases and Microbiology, Imperial College, London, UK
3. Department of Sexually Transmitted Diseases, Royal Free and University College Medical School, Mortimer Market Centre, off Capper Street,
London WC1E 6AU, and HIV/STI Division, PHLS Communicable Disease Surveillance Centre, 61 Colindale Avenue, London NW9 5EQ, UK