1. Department of Epidemiology, University of Washington, Seattle, WA 98195, USA
2. Centre for Microbiology Research, Kenya Medical Research Institute, Nairobi 00200, Kenya
3. Public Health Sciences Division, Fred Hutchinson Cancer Center, Seattle, WA 98109, USA
4. Center for Clinical Research, Kenya Medical Research Institute, Nairobi 00200, Kenya
5. Department of Global Health, University of Washington, Seattle, WA 98195, USA
6. School of Public Health, Jomo Kenyatta University of Agriculture and Technology, Nairobi 00200, Kenya
7. Department of Obstetrics and Gynecology, University of Washington, Seattle, WA 98195, USA