1. Sexually Transmitted and Blood Borne Virus Laboratory, Central Public Health Laboratory, London NW9 5HT, UK.
2. Sexually Transmitted and Blood Borne Virus Laboratory, Central Public Health Laboratory, London NW9 5HT, UK. and Institute of Public Health, Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK.
3. PHLS Antiviral Susceptibility Reference Unit, Division of Immunity and Infection, University of Birmingham Medical School, Birmingham, UK