1. Health Systems Research Unit, South African Medical Research Council, Cape Town, South Africa
2. Division of Social and Behavioural Sciences in the School of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa
3. Perinatal HIV Research Unit, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
4. Department of Behavioral and Social Sciences, Brown University School of Public Health, Providence, RI, USA