About 17 percent of men who have sex with men (MSM) in Chicago are HIV positive—half of whom are unaware of their status, the Chicago Sun-Times reports. The HIV rate of the general male population is estimated at 1.2 percent.

According to new data from the Chicago Public Health Department, black MSM have double the infection rates of their white and Hispanic counterparts, despite not engaging in riskier behavior.

The study, which collected data from 570 Chicago men in the National HIV Behavioral Surveillance program, is the first time that Chicago health officials have used blood tests to determine HIV infection rates among this group. Past estimates have been based on interviews.

“What we found out pretty much confirms what we’ve known for a while,” said Christopher Brown, assistant commissioner of the health department’s STD, HIV and AIDS division. “We need to get a better understanding of the sexual and social networks and address those issues.”

Health officials will work with groups such as the Chicago Black Gay Men’s Caucus to bolster testing efforts and develop culturally sensitive, MSM-focused outreach programming.