[1] Univ Witwatersrand, Charlotte Maxeke Johannesburg Acad Hosp, Dept Internal Med, 7 York Rd, ZA-2193 Johannesburg, South Africa
[2] Univ Witwatersrand, Fac Hlth Sci, 7 York Rd, ZA-2193 Johannesburg, South Africa
[3] Hlth Sci Res Off, 7 York Rd, ZA-2193 Johannesburg, South Africa
[4] Fac Hlth Sci, Sch Publ Hlth, Div Epidemiol & Biostat, 7 York Rd, ZA-2193 Johannesburg, South Africa
[5] Univ Witwatersrand, 7 York Rd, ZA-2193 Johannesburg, South Africa