[1] Univ Witwatersrand, Fac Hlth Sci, Sch Clin Med, Wits Donald Gordon Med Ctr,Dept Internal Med, 7 York Rd, ZA-2193 Johannesburg, South Africa
[2] Univ Witwatersrand, Fac Hlth Sci, Sch Clin Med, Clin HIV Res Unit, 7 York Rd, ZA-2193 Johannesburg, South Africa
[3] Natl Inst Communicable Dis, Ctr HIV & STIs, 1 Modderfontein Rd,2131 Private Bag X4, ZA-2131 Johannesburg, South Africa
[4] Univ Witwatersrand, Fac Hlth Sci, Sch Pathol, 7 York Rd, ZA-2193 Johannesburg, South Africa