[1] Univ London Imperial Coll Sci Technol & Med, Dept Infect Dis & Microbiol, London, England
[2] Univ London Imperial Coll Sci Technol & Med, Dept Infect Dis Epidemiol, London, England
[3] UCL Royal Free & UCL Med Sch, Dept Primary Care, Ctr Sexual Hlth & HIV Res, London, England
[4] UCL Royal Free & UCL Med Sch, Dept Populat Sci, Ctr Sexual Hlth & HIV Res, London, England
[5] UCL Royal Free & UCL Med Sch, Dept Populat Sci, Ctr Sexual Hlth & HIV Res, London, England
[6] HLth Protect Agcy, HIV & STI Dept, Ctr Communicable Dis Surveillance, London, England