[1] Univ Washington, Dept Epidemiol, Seattle, WA 98195 USA
[2] Ctr Dis Control & Prevent, Social & Behav Res & Evaluat Branch, Div STD Prevent, Atlanta, GA USA
[3] San Francisco VA Med Ctr, Dept Veteran Affairs, San Francisco, CA USA
[4] Ctr Dis Control & Prevent, Div STD Prevent, Atlanta, GA USA
[5] Calif Dept Publ Hlth, STD Control Branch, Richmond, CA USA