'First-ever' multi-year data from the U.S. Centers for Disease Control and Prevention revealed progress since the peak of the HIV epidemic in the 1980s, but a sharp increase in infection rates among young black men who have sex with men show there is much more work to do, officials said.

"We're very concerned about these increases among young gay men," Dr. Kevin Fenton, director of the CDC's National Center for HIV/AIDS, told reporters. "We can't allow the health to a new generation to be lost to what is essentially a completely preventable disease."

Men who have sex with men remain the group most heavily affected by new HIV infections, according to a CDC officials. The agency estimates that these cases represent only 2 percent of the U.S. population, and accounted for 61 percent of all new HIV infections in 2009. Young males - ages 13 to 29 - were most severely affected, representing 27 percent of new infections in 2009.

According to the estimates, published in the journal "PLoS ONE," there were 48,600 new HIV infections in the United States in 2006, 56,000 in 2007, 47,800 in 2008 and 48,100 in 2009. Over the four-year period, that amounts to an average of 50,000 cases per year.

“More than 30 years into the HIV epidemic, about 50,000 people in this country still become infected each year.

Not only do men who have sex with men continue to account for most new infections, young gay and bisexual men are the only group in which infections are increasing, and this increase is particularly concerning among young African American MSM ,” said CDC Director Thomas Frieden, M.D.

“HIV infections can be prevented. By getting tested, reducing risky behaviors, and getting treatment, people can protect themselves and their loved ones,” he added.

But communities of color, and especially blacks, were disproportionately affected.

While blacks represent 14 percent of the U.S. population, they accounted for 44 percent of new HIV infections in 2009. HIV infection rates among blacks were nearly eight times higher than rates in whites, according to the study.

Hispanics, who represent about 16 percent of the population, accounted for 20 percent of new HIV infections in 2009 - a rate that was nearly three times as high as that of whites.