1. Center for HIV and STIs, National Institute for Communicable Diseases, National Health Laboratory Service, Johannesburg, South Africa
2. School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3. Centre for the AIDS Programme of Research in South Africa (CAPRISA), KwaZulu Natal, South Africa
4. Department of Epidemiology, Columbia University, New York, New York, USA
5. Division of Medical Virology, Institute of Infectious Disease and Molecular Medicine, University of Cape Town, Cape Town, South Africa