WASHINGTON (Reuters) - Guidelines making AIDS tests part of routine care have helped get more Americans tested, but more than half of adults still have no idea if they are infected, government researchers reported on Tuesday.

Nearly 83 million Americans have been tested for the AIDS virus, 11.4 million of them since the guidelines were issued in 2006, the U.S. Centers for Disease Control and Prevention said.

But 200,000 Americans are infected with the virus and do not know it, CDC director Dr. Thomas Frieden said.

“The numbers show that progress is possible,” Frieden told a news conference.

“They also show that progress is needed,” he added. “To see a steady improvement in just a two or three year period, I think, is quite encouraging. It’s progress but it’s not success.”

The CDC estimates that 1.1 million Americans are infected with the human immunodeficiency virus that causes AIDS, with 56,000 new infections each year.

The CDC’s Dr. Jonathan Mermin said people who do not know they are infected are far more likely to infect someone else with the incurable virus.

“People who know they are positive cut their risky behaviors in half,” Frieden said.

While there is no cure, a cocktail of HIV drugs can keep people healthy and studies also show that HIV patients who take the drugs are less likely to transmit the virus, which is spread in blood, semen and breast milk as well as on needles.

So in 2006, the CDC said that instead of making people ask for HIV tests, in effect admitting they may have engaged in risky behavior, people should be automatically tested unless they opt out. “It should be a normal, routine part of care,” Frieden said.

“Today’s data shows that following those recommendations, there was a significant increase in the number of Americans who were tested for the first time,” he added.

Last year 82.9 million adults between 18 and 64 said they had been tested for HIV -- 11.4 million more than in 2006. In 2006, 40 percent of U.S. adults had been tested and in 2009, 45 percent had.

“Despite this progress, 55 percent of adults, and 28.3 percent of adults with a risk factor for HIV, have not been tested,” the CDC noted.

And 32 percent of people diagnosed with HIV in 2007 progressed to AIDS within 12 months. “In other words, they had unknowingly been infected with HIV for years without being diagnosed,” Mermin said.

On average, it takes 10 years for a person infected with HIV to develop AIDS if he or she is not treated.

Globally, more than 33 million people are infected with HIV, 22.5 million of them in sub-Saharan Africa, according to the United Nations.