[1] Natl Inst Communicable Dis, Ctr HIV & STI, Modderfontein Rd Sandringham, ZA-2192 Johannesburg, South Africa
[2] Univ Witwatersrand, Sch Publ Hlth, Johannesburg, South Africa
[3] Ctr Dis Control & Prevent, Div Global HIV & TB, Pretoria, South Africa
[4] Univ Witwatersrand, Sch Pathol, Div Virol, Johannesburg, South Africa