[1] Harvard Univ, Sch Publ Hlth, Dept Global Hlth & Populat, Boston, MA 02115 USA
[2] Univ KwaZulu Natal, Africa Ctr Hlth & Populat Studies, Mtubatuba, South Africa
[3] Univ Michigan, Sch Med, Ann Arbor, MI USA
[4] Univ Michigan, Sch Publ Hlth, Dept Epidemiol, Ann Arbor, MI 48109 USA
[5] Massachusetts Gen Hosp, Ctr Global Hlth, Boston, MA 02114 USA
[6] UCL Inst Child Hlth, Ctr Paediat Epidemiol & Biostat, London, England