US health officials are reporting that nearly one in five gay and bisexual men in 21 major cities in the U.S. are infected with HIV—and nearly half of them are unaware of it. Young men and especially young black men are least likely to know they’re infected, a study from the U.S. Centers for Disease Control and Prevention found. The study looked at 8,153 men who have sex with men in 21 U.S. cities, and found that 19 per cent of gay men are infected with HIV. Meanwhile, 28 per cent of gay black men are infected with HIV, compared with 18 per cent of Hispanic men and 16 per cent of white men. Black men were also least likely to be aware of their infection in the study: 59 per cent did not know they were infected, compared to 46 per cent of Hispanic men and 26 per cent of white men. The youngest men were especially at risk of being unaware.