1. Partners in Health Research and Development, Centre for Clinical Research, Kenya Medical Research Institute, Nairobi 19865-00202, Kenya
2. Kenyatta National Hospital, Nairobi 20723-00202, Kenya
3. Kenya Medical Research Institute, Nairobi 54840-00200, Kenya
4. Department of Global Health, University of Washington, Seattle, WA 98105, USA
5. School of Public Health, Jomo Kenyatta University of Agriculture and Technology, Nairobi 62000-00200, Kenya