1. Department of Epidemiology and Biostatistics, Memorial Sloan-Kettering Comprehensive Cancer Center, New York, New York.
2. Centers for Disease Control and Prevention, Division of Sexually Transmitted Disease Prevention, Atlanta, Georgia.
3. Department of Epidemiology, University of North Carolina Gillings School of Global Public Health, Chapel Hill, North Carolina.
4. Department of Health Behavior and Health Education, University of North Carolina Gillings School of Global Public Health, Chapel Hill, North Carolina.