[1] KEMRI Wellcome Trust Res Programme, Hlth Serv Unit, Nairobi, Kenya
[2] London Sch Hyg & Trop Med, Dept Med Stat, Fac Epidemiol & Populat Hlth, London WC1E 7HT, England
[3] London Sch Hyg & Trop Med, Dept Populat Hlth, Fac Epidemiol & Populat Hlth, London, England
[4] Kilimanjaro Christian Med Univ Coll, Dept Epidemiol & Biostat, Moshi, Tanzania
[5] Univ Oxford, Ctr Trop Med & Global Hlth, Nuffield Dept Med, Oxford, England