[1] Univ Brighton, Div Primary Care & Publ Hlth, Brighton & Sussex Med Sch, Brighton BN1 9PH, E Sussex, England
[2] MRC Gen Practice Res Framework, London, England
[3] Med & Healthcare Prod Regulatory Agcy, London, England
[4] Agcy Ctr Infect, Dept Microbiol & Epidemiol STIs & HIV, London, England
[5] UCL, Res Dept Infect & Populat Hlth, Ctr Sexual Hlth & HIV Res, London WC1E 6BT, England