[1] Stellenbosch Univ, Tygerberg Hosp, Dept Paediat Child Hlth, Cape Town, South Africa
[2] Stellenbosch Univ, Fac Med & Hlth Sci, Div Epidemiol & Biostat, Cape Town, South Africa
[3] Stellenbosch Univ, Family Ctr Res Ubuntu, Dept Paediat & Child Hlth, Stellenbosch, South Africa
[4] Univ Witwatersrand, Chris Hani Baragwanath Acad Hosp, Fac Hlth Sci, Perinatal HIV Res Unit, Johannesburg, South Africa
[5] Univ Witwatersrand, Fac Hlth Sci, Sch Publ Hlth, Johannesburg, South Africa
[6] Univ Calif San Diego, Sch Publ Hlth, La Jolla, CA USA
[7] Univ Calif San Diego, Sch Publ Hlth, Div Biostat & Bioinformat, La Jolla, CA USA
[8] Univ Cape Town, Desmond Tutu HIV Ctr, Cape Town, South Africa