This is no longer just a disease of men who have sex with men,"

This is no longer just a disease of men who have sex with men," Feinberg said. "If you're a sexually active person, you're at risk of getting HIV no matter who you have sex with."

Half of the new infections and half the people living with AIDS are African-American. And half are among men who have sex with men.

One-fifth of people in the U.S. who are infected don't know it, according to the CDC.

"Somewhere out there are a quarter-million people who have HIV and don't know it," Feinberg said. "Since they don't know it, they can't alter their behavior."

And that means they can spread the disease and may miss the health benefits of starting treatment early, Feinberg said.

The activist group AIDS Action used World AIDS Day to call on Congress to pass health reform that would end the insurance industry practice of denying coverage to patients with pre-existing conditions. And, according to deputy executive director Ronald Johnson, Congress should drop the ban on federal funds for needle exchange programs aimed at reducing the transmission among illegal drug users of HIV-AIDS through dirty syringes. The needle exchanges can save the country money since it costs $700,000 over a lifetime to treat someone who is infected, Johnson said. "The human and health care costs are too great to continue to reject this prevention technique that has proved to be effective," he said.

Huang said former President George W. Bush's plan to spend billions fighting AIDS in Africa has stabilized the situation there. Still, of the 33.4 million people in the world living with HIV, 22.4 million of them live in sub-Saharan Africa, according to UNAIDS.

And Feinberg warned that Americans can't assume they are safe from the disease. "It's not melting away, and people shouldn't have the attitude it's somewhere else."