[1] Univ London London Sch Hyg & Trop Med, Dept Infect & Trop Dis, MRC, Trop Epidemiol Grp, London WC1E 7HT, England
[2] Mahidol Univ, Sexually Transmitted Infect Clin, Dept Dermatol, Bangkok 10700, Thailand
[3] Univ Sherbrooke, Ctr Int Hlth, Quebec City, PQ, Canada
[4] Mahidol Univ, Dept Microbiol, Bangkok 10700, Thailand
[5] Inst Child Hlth, Ctr Int Child Hlth, London, England
[6] Minist Publ Hlth, Div Epidemiol, Bangkok, Thailand
[7] Mahidol Univ, Dept Obstet & Gynaecol, Bangkok 10700, Thailand
[8] London Sch Hyg & Trop Med, Dept Epidemiol & Populat Hlth, London WC1, England