1. Department of Epidemiology, Harvard School of Public Health, 1633 Tremont Street, Boston, MA 02115, USA
2. Department of Nutrition, Harvard School of Public Health, Boston, MA, USA
3. Department of Microbiology and Immunology, Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania
4. Department of Community Health, Muhimbili University of Health and Allied Sciences, Dar es Salaam, Tanzania
5. Department of Biostatistics, Harvard School of Public Health, Boston, MA, USA
6. Department of Global Health and Population, Harvard School of Public Health, Boston, MA, USA