1. Department of Urban Public Health, Manning College of Nursing and Health Sciences, University of Massachusetts Boston, Boston, MA, USA
2. Population Studies & Training Center, Brown University, Providence, RI, USA
3. International Health Institute and Departments of Epidemiology and Anthropology, School of Public Health, Providence, RI, USA
4. Medical Research Council/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