[1] Family Hlth Int, Res Triangle Pk, NC 27709 USA
[2] Univ KwaZulu Natal, Nelson R Mandela Sch Med, CAPRISA, Durban, South Africa
[3] Univ KwaZulu Natal, Nelson R Mandela Sch Med, Dept Publ Hlth & Family Med, Durban, South Africa
[4] Columbia Univ, Mailman Sch Publ Hlth, Div Epidemiol, New York, NY USA