That adds up to a lot of people who are vulnerable to declining immune systems and ultimately, the terrible infections of AIDS. About 17,000 Americans still die of AIDS every year.

Even in places doing the best job of testing people for HIV and getting them into treatment, there's a long way to go.

In San Francisco, which has one of the nation's highest concentrations of HIV-positive people, 60 to 70 percent of them are getting effective treatment, says Dr. Grant Colfax, the city's director of AIDS prevention and research. But that means, of course, that even San Francisco hasn't been able to get as many as 40 percent of its HIV-infected population into long-term treatment.

"It's not sufficient to provide people with one doctor's appointment after the diagnosis," Colfax told Shots. "It's very important to give that person the social and emotional support, as well as the medical support, they need to engage in care."

That's not easy to do. But the implications of not doing it go beyond the already-infected to the not-yet-infected. Last spring a large study confirmed what AIDS researchers have long hoped: that suppressing HIV with antiviral drugs makes treated people much less likely to infect others — 96 percent less likely.

"This is a very important finding," Frieden says. "For too many years, there has sometimes been friction between treatment and prevention. This study brings home that treatment is prevention. Treatment is essential to prevention."

And not treating people with HIV is probably the most expensive mistake the nation can make in the 30-year-old war against the disease. Without "substantial improvement" in rates of effective treatment, the CDC says, there will be 1.2 million new HIV infections in the U.S. over the next 20 years.

Since it costs $367,000 (in 2009 dollars) to treat each infected patient over a lifetime, those avoidable infections will cost the nation nearly a half-trillion dollars.

As usual, the HIV burden is not equal. The new report shows that African-American men have the lowest rates of effective antiviral treatment. Of people who are actually getting any antiviral treatment, only 70 percent of black men have good suppression of HIV in their blood, compared to 84 percent of whites and 79 percent of Hispanics.