1. School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
2. Health Economics and Epidemiology Research Office, Department of Internal Medicine, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
3. Clinical HIV Research Unit, Department of Internal Medicine, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
4. Department of Public Health, School of Health Sciences, Monash University, Johannesburg, South Africa.