[1] Univ Cape Town, Fac Hlth Sci, Ctr Infect Dis Epidemiol & Res, ZA-7925 Cape Town, South Africa
[2] Chris Hani Baragwanath Hosp, Harriet Shezi Childrens Clin, Johannesburg, South Africa
[3] Univ Witwatersrand, Fac Hlth Sci, Wits Reprod Hlth & HIV Inst, Johannesburg, South Africa
[4] Univ Witwatersrand, Fac Hlth Sci, Dept Mol Med & Haemotol, Johannesburg, South Africa
[5] Natl Hlth Lab Serv, Johannesburg, South Africa
[6] Univ KwaZulu Natal, Africa Ctr Hlth & Populat Studies, Durban, South Africa
[7] Univ Glasgow, Div Dev Med, Glasgow, Lanark, Scotland
[8] Univ Cape Town, Ctr Actuarial Res, ZA-7925 Cape Town, South Africa
[9] UCL, Inst Child Hlth, Ctr Paediat Epidemiol & Biostat, London, England