HIV is hitting gay black men particularly hard (a 2005 study showed the prevalence rate among young, gay black men in five U.S. cities was nearly 50%) and now researchers believe they may know part of the reason why: prejudice and racism.

A survey of nearly 1,150 men who have sex with men in San Francisco, reported in the journal AIDS and Behavior, has shown that black gay men had a threefold higher level of same-race partnering than other racial groups, mostly due to the survey's findings that blacks were deemed the least preferred as sexual partners by men of other ethnicities. Being shunned by other gay men forces gay black men into closely knit sexual networks that allow HIV to rapidly spread once introduced.