[1] London Sch Hyg & Trop Med, Int Ctr Eye Hlth, Dept Infect & Trop Dis, Clin Res Dept, London WC1E 7HT, England
[2] Queens Univ, Sch Med Dent & Biomed Sci, 97 Lisburn Rd, Belfast BT9 7BL, Antrim, North Ireland
[3] Univ Colombo, Dept Sociol, Reid Ave, Colombo 03, Colombo, Sri Lanka
[4] London Sch Hyg & Trop Med, Int Ctr Evidence Disabil, Dept Infect & Trop Dis, Dept Clin Res, London WC1E 7HT, England