1 Centre for the AIDS Programme of Research in South Africa, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa.
2 Centre for the AIDS Programme of Research in South Africa, Nelson R Mandela School of Medicine, University of KwaZulu-Natal, Durban, South Africa; Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, NY, USA. Electronic address: quarraisha.abdoolkarim@caprisa.org.