1. Boston University School of Public Health, Boston, MA, USA.
2. Division of Prevention Science, Department of Medicine, University of California San Francisco, San Francisco, CA, USA.
3. MRC-Wits Rural Public Health and Health Transitions Research Unit (Agincourt), School of Public Health, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
4. Department of Global Health and Population, Harvard T.H. Chan School of Public Health, Boston, MA, USA.