1. Centre for Microbiology Research, Kenya Medical Research Institute (KEMRI), Nairobi, Kenya
2. Family AIDS Care & Education Services, Kisumu, Kenya
3. Department of Obstetrics, Gynecology & Reproductive Sciences, University of California, San Francisco, CA, USA
4. Department of Pediatrics, University of Colorado, Aurora, CO, USA
5. Department of Epidemiology and Biostatistics, University of California, San Francisco, CA, USA