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