A new study from the San Francisco Department of Public Health suggests that black men have an increased risk of HIV because they have closely connected sexual networks and fewer partners to choose from, Pink News reports.

According to the article, 1,142 men who have sex with men (MSM) were interviewed and asked about their ethnicity, sexual partners in the past six months, perception of how easy it is to meet sexual partners of different races, where they meet partners and their view of HIV infection risk. They were three times more likely to have sexual partners of the same race.

The study found that compared to other races, black men were the least preferred sexual partners and they were also perceived as being riskier to have sex with.

“The racial disparity in HIV observed for more than a decade will not disappear until the challenges posed by a legacy of racism towards blacks in the U.S. are addressed,” concluded the study.

In 2006, black Americans accounted for almost half of all HIV/AIDS cases—four times the national average.