1Division of Sexually Transmitted Disease/HIV Prevention, National Center for Prevention Services, Atlanta, GA
3Division of Reproductive Health, National Center for Chronic Disease Prevention and Health Promotion, Atlanta, GA
4Division of Sexually Transmitted Diseases, Laboratory Research, National Center for Infectious Diseases, Centers for Disease Control and Prevention (CDC),Atlanta, GA
2Asociación Demográfica Costarricense, San José, Costa Rica
5Department of Pediatrics, Division of Pediatric Infectious Diseases, Epidemiology and Immunology, Emory University School of Medicine, Atlanta, GA
6Departments of Epidemiology and Laboratory Medicine, University of California, San Francisco, CA. Participants are listed in the Appendix.