1. Division of Medicine, Imperial College London, St Mary's Hospital, London W2 1NY, UK
2. Department of Microbiology/Oral Surgery, Eastman Dental Institute, Gray's Inn Road, London W1CX 8LD, UK
3. Central Public Health Laboratory, 61 Colindale Avenue, London NW9 5HT
4. Department of Genitourinary Medicine, St George's Hospital, London SW17 0QT, UK