ATLANTA, GA: A new Centers for Disease Control (CDC) study showed that 1- in-5 gay and bisexual men in 21 major U.S. cities are infected with HIV and nearly half of them don’t know it. Young men, especially young black men, are least likely to know if they are infected with HIV, according to the study. Researchers studied 8,153 gay and bisexual men. The men were taking part in the 2008 National HIV Behavioral Surveillance Study which looked at prevalence and awareness of HIV, the virus that causes AIDS. Overall, they found that 19 percent of gay men are infected with HIV.