1. Centre for HIV and STI National Institute for Communicable Diseases Johannesburg South Africa
2. School of Public Health University of the Witwatersrand Johannesburg South Africa
3. Biostatistics Unit South African Medical Research Council Cape Town South Africa
4. Biostatistics Unit South African Medical Research Council Pretoria South Africa
5. Department of Statistics University of Pretoria Pretoria South Africa
6. Centers for Disease Control and Prevention Pretoria South Africa
7. Division of Virology School of Pathology University of the Witwatersrand Johannesburg South Africa