1. Gertrude H. Sergievsky Center, College of Physicians and Surgeons, Columbia University, New York, New York;
2. Center for AIDS Prevention Studies, Department of Medicine, University of California, San Francisco;
3. Empilweni Services and Research Unit, Rahima Moosa Mother and Child Hospital, Department of Paediatrics and Child Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa;
4. Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York;
5. Centre for HIV and STIs, National Institute for Communicable Diseases, Johannesburg, South Africa;
6. ICAP, Mailman School of Public Health, and
7. Department of Pediatrics, College of Physicians & Surgeons, Columbia University, New York, New York.