[1] UCL Hosp, Patrick Mason Unit, NHS Trust, London WC1E 6AU, England
[2] Royal Free & Univ Coll, Sch Med, Dept Histopathol, London, England
[3] UCL, Royal Free & Univ Coll Med Sch, Ctr Sexual Hlth & HIV Res, Dept Primary Care & Populat Sci, London WC1E 6JJ, England
[4] Mortimer Mkt Ctr, Camden PCT, Dept Genitourinary Med, London WC1E 6AU, England