ATLANTA - Fewer black women in the United States are being infected with HIV, but the number of young gay and bisexual men infected is rising, the Centers for Disease Control and Prevention said on Wednesday. 

Between 2008 and 2010, the number of newly infected black women dropped 21 percent, according to the CDC report. Yet despite the decline, they still accounted for 70 percent of all new HIV cases among women, the federal health agency said.

The rate of new infections for black women was 20 times higher than the rate for white women, the CDC said.

The number of new infections among young gay and bisexual men increased by 22 percent during that same two-year period, the CDC said.

The number of new HIV infections diagnosed annually in the overall U.S. population remained unchanged between 2008 and 2010 at about 47,500, according to health officials.

Public information campaigns on HIV prevention and testing seem to be working in lowering the number of new infections among African-American women, said Joseph Prejean, chief of the Behavioral and Clinical Surveillance Branch in the CDC's division of HIV/AIDS Prevention in Atlanta.

"We are encouraged to see some declines among African-American women," Prejean told Reuters. "They've been one of the most severely affected populations. We're cautiously optimistic that this could be part of a longer-term trend."

Among young gay and bisexual men, efforts to fight HIV have not been as effective, possibly because of advances in treatment for AIDS, the immune disorder caused by HIV, Prejean said.

"We do realize that many men who have sex with men do probably underestimate their personal risk and believe that treatment advances minimize the health threat," Prejean said.

Even though treatment can prolong the life of an AIDS patient, Prejean cautioned that "their life really does change. They then begin to take medication and will take medication for the rest of their lives," he said.

HIV is an incurable infection that costs $400,000 to treat over a lifetime, CDC Director Dr. Thomas Frieden said last month after another government report showed more than half of young Americans infected with HIV were not aware they had it.

Young people ages 13 to 24 account for 26 percent of all new HIV infections in the United States, the earlier CDC report said.

The report released on Wednesday said nearly two-thirds of new HIV infections in 2010 resulted from men having sex with other men. Young black men who have sex with men account for more new infections than any other subgroup, government health officials said.

"Because gay men account for 66 percent of all new infections, we must increase the focus of our prevention programs for gay men, particularly young and black gay men," said Michael Ruppal, executive director of The AIDS Institute.