1. College of Nursing, Washington State University, Spokane, WA, USA
2. Centre for Public Health Research, Kenya Medical Research Institute, Nairobi, Kenya
3. Centre for Clinical Research, Kenya Medical Research Institute, Nairobi, Kenya
4. Department of Physiological Nursing, School of Nursing, University of California, San Francisco, San Francisco, CA, USA
5. Department of Epidemiology and Biostatistics, School of Medicine, University of California, San Francisco, San Francisco, CA, USA