[1] Natl Inst Communicable Dis, Ctr HIV & STI, 1 Modderfontein Rd, ZA-2192 Johannesburg, South Africa
[2] Univ Witwatersrand, Sch Publ Hlth, Johannesburg, South Africa
[3] South African Med Res Council, Biostat Unit, Cape Town, South Africa
[4] South African Med Res Council, Biostat Unit, Pretoria, South Africa
[5] Univ Pretoria, Dept Stat, Pretoria, South Africa
[6] US Ctr Dis Control & Prevent, Div Global HIV AIDS & TB, Sci, Pretoria, South Africa
[7] US Publ Hlth Serv Commissioned Corps, Rockville, MD USA
[8] US Ctr Dis Control & Prevent, Div Global HIV AIDS & TB, Pretoria, South Africa
[9] Univ Witwatersrand, Sch Pathol, Div Virol, Johannesburg, South Africa