Less than a third of people living with HIV/AIDS in the United States are in successful enough treatment that they will remain healthy and reduce the likelihood of transmitting the virus to their sexual partners, according to the the Centers for Disease Control and Prevention. Health officials believe they must dramatically boost that number in order to control the epidemic, which has ravaged black communities in particular and is [still growing among black gay and bisexual men](http://colorlines.com/archives/2011/08/hiv_epidemic_growing_fastest_amon...). The CDC released its latest update on the HIV/AIDS epidemic on Tuesday, in advance of World AIDS Day on Dec. 1. This spring marked 30 years since the public health agency first reported on the condition that would later be identified as HIV infection. Roughly half of those living with HIV/AIDS in the U.S. are black, as are roughly half of those who are newly infected each year. Reducing what's called a patient's "viral load" is a core part of HIV treatment. The more virus that's circulating in your blood, the weaker your immune system becomes and the more likely you are to develop a fatal illness. Treatment specialists believe a viral count under 550 copies of the virus per milliliter of blood is the magic number to stay healthy; go above that mark and you should start taking anti-retroviral drugs, they say. But CDC officials have also said that a viral load below 200 meaningfully reduces the risk of transmitting the virus to a sexual partner. Tuesday, the CDC reported that only 28 percent of the estimated 1.2 million Americans living with HIV have viral counts that low. That news comes as a dampener to big, promising news earlier this year, when researchers found that successful treatment lowered the likelihood of transmitting HIV by a shocking 96 percent. Federal health officials also estimate that 20 percent of people with the virus remain unaware altogether of their status because they have not been tested. CDC has long pointed out that new infections are driven overwhelmingly by people who don't know they are HIV positive. Still, the findings released Tuesday suggest that many people who have been tested and have gotten into treatment aren't succeeding in lowering their viral loads. Moreover, there appears to be a racial disparity in who is and is not succeeding. A 2009-2010 study of adults with HIV in New York City, Los Angeles County, Philadelphia, Florida, Puerto Rico and 18 other jurisdictions found that 80 percent of white patients and 79 percent of Latino patients who received anti-retroviral therapy saw their viral levels fall below the 200 threshold. But only 70 percent of black patients who received treatment suppressed their viral counts. Jonathan Mermin, director of the Division of HIV/AIDS Prevention at the National Center for HIV/AIDS, Viral Hepatitis, STD and Tuberculosis Prevention, conceded Tuesday it "is not completely known" what causes that racial disparity. He pointed out that there are "a lot of challenges even among those prescribed ART" that could come into play. Black communities overall suffer higher rates of unemployment and poverty that block access to health care. Access to transportation, homophobia, stigma or even migration are other potential factors getting in the way of more successful treatment. Previous studies have also found that African Americans arrive in treatment late in the life of their HIV infection--which means, like any other health problem, it's far more difficult to treat successfully. "We know that anti-retroviral therapy is available and effective," said Janet Weinberg of Gay Men's Health Crisis. "However, we have to increase access to treatment and provide culturally competent education, training and counseling--especially in communities where there are higher rates of HIV." The CDC's concern about viral loads as a matter of HIV prevention, not just treatment, reflects a growing emphasis in public health on what's called biomedical prevention of the virus's spread. Researchers are [exploring microbicides](http://colorlines.com/archives/2011/02/microbicides_could_forever_change...) that could block transmission. Others are developing the use of [anti-retroviral drug regimens for people who are negative](http://colorlines.com/archives/2011/07/in_the_fight_against_hiv_a_breakt...), as a way to stop transmission from a positive sexual partners. And public health officials are increasingly focused on treatment of people who are positive as prevention. In May, a National Institutes of Health study of heterosexual couples found that people who begin HIV treatments while their immune systems remain relatively strong are [96 percent less likely to pass the virus](http://colorlines.com/archives/2011/05/equal_access_to_hiv_treatment_cou...) along to partners. "This is a very important finding because it shows that treatment for HIV can prevent the spread of HIV to others," said CDC Director Thomas Frieden.