[1] Univ Copenhagen, Dept Publ Hlth, Oster Farimagsgade 5, DK-1014 Copenhagen, Denmark
[2] Manicaland Ctr Publ Hlth Res, Biomed Res & Training Inst, Harare, Zimbabwe
[3] London Sch Hyg & Trop Med, Dept Global Hlth & Dev, London, England
[4] Imperial Coll London, Dept Infect Dis Epidemiol, London, England