1. Empilweni Services and Research Unit, Rahima Moosa Mother and Child Hospital, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
2. ICAP, Mailman School of Public Health, Columbia University, New York, New York3Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York
3. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York4Gertrude H. Sergievsky Center, College of Physicians and Surgeons, Columbia University, New York, New York
4. Center for HIV and STIs, National Institute for Communicable Diseases, Johannesburg, South Africa
5. Department of Biostatistics, Mailman School of Public Health, Columbia University, New York, New York