If current HIV diagnosis rates persist, about half of all gay black men and a quarter of gay Latino men in the United States will be infected with HIV in their lifetime, according to a new report from the Centers for Disease Control and Prevention.

The findings, which represent the first-ever projections of lifetime risk of HIV infection in the U.S., were presented today at the Conference on Retroviruses and Opportunistic Infections in Boston.

"As alarming as these lifetime risk estimates are, they are not a foregone conclusion. They are a call to action," Dr. Jonathan Mermin, director of CDC's National Center for HIV/AIDS, Viral Hepatitis, STD, and Tuberculosis Prevention, said in a statement. "The prevention and care strategies we have at our disposal today provide a promising outlook for future reductions of HIV infections and disparities in the U.S., but hundreds of thousands of people will be diagnosed in their lifetime if we don't scale up efforts now."

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For the study, researchers used data on diagnoses and death rates from 2009 to 2013 to project the lifetime risk of HIV diagnosis in the U.S. by sex, race and ethnicity, state, and HIV risk group.

Though overall, the lifetime risk of HIV diagnosis in the U.S. is now 1 in 99 -- a huge improvement from the reported overall risk of 1 in 78 about a decade ago -- large disparities still exist.

Gay and bisexual men continue to be at the greatest risk. If diagnosis rates remain constant, 1 in 6 males who have sex with other males will be diagnosed with HIV in their lifetime.

African-Americans continue to be the most disproportionately affected racial or ethnic group, with a lifetime HIV risk of 1 in 20 for men and 1 in 48 for women.

For whites, those numbers are 1 in 132 for men and 1 in 880 for women.

The CDC reports several challenges related to prevention contributing to higher HIV infection rates in the African-American community.

First, since people tend to have sex with partners of the same race, and since African-Americans have the highest rate of HIV, people in this group face a greater risk of infection with each new sexual encounter.

African-Americans also have higher rates of other sexually transmitted diseases, which can significantly increase a person's chance of getting or transmitting HIV.

Socioeconomic issues, including poverty, limited access to high-quality health care, housing and HIV prevention education are also factors.

Finally, in many communities, stigma also plays a role.

"There are still a lot of people in hiding whispering about HIV," Maria Davis, an African-American former hip-hop promoter and current HIV/AIDS advocate and educator who has lived with HIV for over 20 years, told CBS News. "Stigma in the African-American community has gotten better, but it's still there. I still have people coming up to me and asking me if you can get HIV by eating behind someone or using the bathroom after someone who's HIV positive or hugging someone who has HIV, and I have to tell them, 'No, you can't get HIV that way.'"

Davis currently does outreach in Harlem, educating the community about HIV/AIDS and encouraging everyone to get tested. "It's so important to get tested and know your HIV status," she said, "so that when you're spreading the message to your partners, your family, your neighbors, your friends that you're accurate and you can say I'm HIV negative or I'm HIV positive and here's the information that I can offer to you to help you live a long, healthy life."

In addition to HIV testing, ongoing care and treatment for people living with HIV, and condom use, the CDC recommends people at high risk for HIV take pre-exposure prophylaxis (PrEP), a daily anti-HIV pill.

In December, another government report found that 1 in 4 sexually active gay and bisexual men should be taking the daily medications to help reduce their risk of infection, but many who could benefit from the pills aren't getting them.

The CDC urges doctors to test patients for HIV as part of routine medical care, follow PrEP clinical practice guidelines and counsel patients who can benefit from the drug on how to take it every day. Patients may also need help applying for insurance or other programs to pay for it.

The latest CDC study also highlighted the fact that people who inject drugs are far more likely to get HIV, with the risk estimated at 1 in 23 for women and 1 in 36 for men.

People living in the South are also at a greater lifetime risk of HIV, with the highest rates projected in Washington, D.C. (1 in 13 people), Maryland (1 in 49), Georgia (1 in 51), Florida (1 in 54), and Louisiana (1 in 56).

But the CDC is hopeful that these projections do not have to become a reality.

"These estimates are a sobering reminder that gay and bisexual men face an unacceptably high risk for HIV - and of the urgent need for action," said Eugene McCray, M.D., director of CDC's Division of HIV/AIDS Prevention. "If we work to ensure that every American has access to the prevention tools we know work, we can avoid the outcomes projected in this study."