One in five gay men living in 21 major US cities are infected with the AIDS virus and nearly half are unaware of it, the Centers for Disease Control and Prevention (CDC) said in a study.
The CDC said that from 2005 to 2008 HIV infection among gays increased 17 percent.
Nineteen percent of "men who have sex with men" are HIV positive and 44 percent of those men are unaware of their infection, said the CDC study of more than 8,000 gays published Thursday in its Morbidity and Mortality Weekly Report.
"This study's message is clear: HIV exacts a devastating toll on men who have sex with men in America's major cities... We need to increase access to HIV testing so that more ... know their status," said CDC National Center for HIV/AIDS director Kevin Fenton.
While gays of all ethnicities are affected by AIDS, blacks were more heavily impacted (28 percent), followed by Hispanics (18 percent) and whites (16 percent), the study found.
Among those unaware they are HIV positive, the ethnic disparity was the similar: 59 percent of blacks, 46 percent of Hispanics and 26 percent of whites, it added.
The study also found "a strong link" between socioeconomic status and HIV among men who have sex with men.
It said the prevalence increased as education and income decreased, and awareness of HIV status was higher among gay men with greater education and income.