[1] Tygerberg Hosp, Dept Paediat & Child Hlth, Cape Town, South Africa
[2] Stellenbosch Univ, Cape Town, South Africa
[3] Family Ctr Res Ubuntu FAMCRU, Cape Town, 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, Dept Med, La Jolla, CA USA
[7] Univ Cape Town, Desmond Tutu HIV Ctr, Cape Town, South Africa
[8] Tygerberg Hosp, Dept Paediat & Child Hlth, POB 241, ZA-8000 Cape Town, South Africa
[9] Stellenbosch Univ, POB 241, ZA-8000 Cape Town, South Africa