1. Department of Epidemiology University of Washington Seattle WA USA
2. Department of Global Health University of Washington Seattle WA USA
3. Centre for Microbiology Research Kenya Medical Research Institute Nairobi Kenya
4. Departments of Obstetrics and Gynecology University of Washington Seattle WA USA
5. Department of Biostatistics University of Washington Seattle WA USA
6. Department of Medicine University of Washington Seattle WA USA