1. 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
2. Department of Global Health, Boston University School of Public Health, Boston, MA, USA
3. Department of Epidemiology, Boston University School of Public Health, Boston, MA, USA
4. Health Systems Research Unit, South African Medical Research Council, Cape Town, South Africa
5. Empilweni Services and Research Unit, Department of Paediatrics and Child Health, University of the Witwatersrand, Rahima Moosa Mother and Child Hospital, Johannesburg, South Africa