1. Harvard Center for Population and Development Studies, Harvard University, Cambridge, MA, USA
2. Division of Infectious Diseases, Brigham and Women’s Hospital, Boston, MA, USA
3. MRC/Wits Rural Public Health and Heath Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, University of Witwatersrand, Johannesburg, South Africa
4. Heidelberg Institute of Global Health, Heidelberg University, Heidelberg, Germany