[1] St Marys Hosp, Imperial Coll, Sch Med,Dept GU Med & Communicable Dis, Jefferiss Trust Res Labs, London W2 1NY, England
[2] Chelsea & Westminster Hosp, HIV Epidemiol Unit, London SW10 9TH, England
[3] Univ Edinburgh, Sch Med, Dept Med Microbiol, Edinburgh EH8 9AG, Midlothian, Scotland