1. Research Unit, Foundation for Professional Development, Pretoria, South Africa
2. Anova Health Institute, Johannesburg, South Africa
3. Department of Medical Microbiology, Faculty of Health Sciences, University of Pretoria, Pretoria, South Africa
4. Department of Epidemiology and Biostatics, School of Public Health and Family Medicine, University of Cape Town, Cape Town, South Africa
5. David Geffen School of Medicine, UCLA, Los Angeles, CA, USA
6. Department of Epidemiology, University of California Los Angeles, Los Angeles, CA, USA
7. School of Public Health and Family Medicine, Faculty of Health Sciences, University of Cape Town, Cape Town, South Africa