MONDAY, Dec. 3 (HealthDay News) -- Two new U.S. studies of gay and bisexual men who know they are infected with HIV show that more than one-third have recently had unprotected intercourse.

In many cases, these men are engaging in unprotected sex with other HIV-infected men -- a practice called "serosorting," where partners with a similar, HIV-positive blood test status decide to forego condoms.

However, "we also found that almost a third of the men -- 31.4 percent -- said that they had had unprotected anal intercourse with at least one partner of unknown serostatus, and almost a quarter had unprotected intercourse with a partner who they knew was HIV uninfected," said the lead author of one of the studies, Dr. Kenneth Mayer, medical research director at Fenway Community Health, in Boston.

He and other researchers in HIV/AIDS presented their findings during a teleconference Monday, part of the U.S. Centers for Disease Control and Prevention's National HIV Prevention Conference, in Atlanta.

"There are now more than one million people estimated to be living with HIV in the United States, more than ever before," said Dr. Kevin Fenton, director of the CDC's National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention.

He also noted that half of all U.S. cases of HIV infection still occur among "men who have sex with men" (MSM), the CDC's umbrella term for gay and bisexual men, as well as men who may not identify as such but engage in male-male sexual activity.

And, Mayer added, unsafe sex was strongly linked to the use of recreational drugs, particularly methamphetamine, and was 60 percent more likely among younger men than older men.

The HIV epidemic in the United States may, in fact, be on the rise. According to recent media reports, sources close to CDC statisticians say that the annual rate of new HIV infections in the United States may soon be bumped up by 50 percent -- jumping from 40,000 new cases annually to up to 60,000.

While not confirming the statistics, Fenton told reporters that a new method for computing HIV infections is being used by the CDC. "The new estimates are not final," he said, adding that the numbers "are still undergoing rigorous analysis and scientific review to ensure the accuracy of both the new methods and of the estimates."

New statistics on rates of unprotected sex among gay and bisexual men are more certain, however. In Mayer's analysis, researchers had more than 500 Boston-area HIV-infected gay or bisexual men complete "behavioral risk assessments." Three-quarters of the men were white, with ages ranging from 21 to 70.

The research team found that 37.3 percent of the men said they had engaged in unprotected anal intercourse over the past three months. In 41.3 percent of these cases, unsafe sex took place with another HIV-infected partner, but in 31.4 percent of cases the unprotected behavior took place with a partner whose HIV status was unknown. In 23 percent of cases, the infected man engaged in unprotected sex with a partner he knew to be HIV-negative, the study found.

Another study, this one led by CDC researcher Nicole Crepaz, found similar results. Her team reviewed data from 27 studies published between 2000 and 2006. The studies included more than 10,000 gay or bisexual men who knew they were HIV-positive.

"The team found that more than a third -- or about 35 percent -- of men in the studies reported having unprotected intercourse overall," Fenton said at the news conference. Again, "serosorting" was found to be widespread, with 30 percent of the men admitting to that practice, the study found.

Black gay and bisexual men, especially, have been hit hard by HIV/AIDS, but another study showed them to be more likely to engage in safe-sex practices than their white counterparts.

In another CDC study, researchers examined data from 53 studies conducted from 1980 to 2006. The studies compared the safe-sex behaviors of black and white gay and bisexual men.

"Across all studies, there were no overall differences [by race] in reported unprotected receptive sex or any unprotected anal intercourse," said the study's lead author, Gregorio Millet, a behavioral scientist at the CDC. In fact, "among young MSM -- those ages 15 to 29 -- African-Americans were one third less likely than whites to report in engaging in unprotected anal intercourse," he said.

Black gay or bisexual men were also "36 percent less likely than whites to report having as many sex partners as white MSM," he added. Blacks in the study were also less likely to use recreational drugs, such as methamphetamine or cocaine, compared to whites.

Other studies presented at the teleconference showed close correlations between recent spikes in syphilis and gonorrhea among gay and bisexual men and rates of HIV infection in this population.

And, in a finding that puzzled experts, another study showed that circumcision -- long thought to reduce HIV infectivity -- does not help shield black or Latino men from the virus.

All of the new statistics confirm that much more must be done, the experts said.

"This shows that prevention messages have to be continually refreshed, and responsive to those who are younger," Mayer said.

More information

There's more on HIV/AIDS at the U.S. Centers for Disease Control and Prevention.

SOURCES: Dec. 3, 2007, teleconference, U.S. Centers for Disease Control and Prevention's National HIV Prevention Conference, Atlanta, with Kenneth Mayer, M.D., Ph.D., medical research director, Fenway Community Health, Boston; Kevin Fenton, M.D., director, National Center for HIV/AIDS, Viral Hepatitis, STD and TB Prevention (NCHHSTP), CDC, Atlanta; Gregorio Millet, behavioral scientist, NCHHSTP, CDC

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