The bisexual bridge revisited: sexual risk behavior among men who have sex with men and women, San Francisco, 1998-2003.

From 1998 to 2003 in San Francisco, unprotected anal intercourse (UAI) with one or more partner of unknown HIV serostatus (potentially serodiscordant UAI) increased among bisexual men who have sex with men (MSM) in parallel and in magnitude compared with other MSM. Potentially serodiscordant UAI and unprotected vaginal intercourse increased from 1998 to 2001 then decreased from 2001 to 2003. Although elements of a 'bisexual bridge' are present, we note an encouraging decrease in risk from 2001 to 2003.