1. Department of Epidemiology, Milken School of Public Health, George Washington University, Washington, District of Columbia, USA.
2. HIV/AIDS, Hepatitis, STD and TB Administration, District of Columbia Department of Health, Washington, District of Columbia, USA.
3. District of Columbia Cancer Registry, District of Columbia Department of Health, Washington, District of Columbia, USA.
4. Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, Georgia, USA.