1. PHLS Antiviral Susceptibility Reference Unit, Division of Immunity and Infection, University of Birmingham Medical School, Birmingham,1
2. Department of Genito-Urinary Medicine, Guys and St. Thomas' NHS Trust,2 and
3. Department of Virology, St. Georges Hospital,3 London,
4. Department of Infectious Diseases, Leicester Royal Infirmary, Leicester,4 and
5. Department of Infectious Diseases, Gartnavel Hospital, Glasgow,5 United Kingdom