Just over 40% of the adult U.S. population has been screened at least once for HIV, but a quarter of a million people are infected and don’t know it, government researchers said Thursday.

About 10% of the population gets an HIV test each year -- a figure that has remained stable since 2000 despite efforts to increase testing -- according to a report from the federal Centers for Disease Control and Prevention.

The release of the data was timed to coincide with the International AIDS Conference being held this week in Mexico City.

About 56,300 Americans become infected with HIV each year, and 1 million to 1.1 million are thought to be living with the virus.


In September 2006, the CDC recommended that all Americans be offered HIV testing as part of their routine medical care.

Last year, the agency allocated additional funds to 23 jurisdictions to test an extra 20 million people, primarily African Americans, in hopes of identifying 20,000 more HIV-positive people.

The goal of the increased testing is to identify infections at an earlier stage so people can begin receiving anti-AIDS drugs while the treatment can do more good. Late diagnosis increases the likelihood that the infection will proceed to more serious illness.

In 2005, 38% of those newly diagnosed with HIV infections progressed to AIDS within a year, the report says.


In addition, an HIV-positive individual who is unaware of the infection is three times as likely to transmit the virus as one who knows his or her status, CDC officials said.

The new data, current through 2006, were collected to serve as a baseline so that officials can judge the success of the accelerated testing program.

The results were obtained from the National Health Interview Survey, in which periodic face-to-face interviews are conducted with people ages 18 to 64 in a broad cross section of the population.

The cumulative data indicate that in 1987, only 6% of the population had ever been tested. In the 1990s, as many as 15% of Americans were tested each year, and the total who had ever been tested reached 38% by 2000.


Since then, the total has remained stable at about 40%.

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thomas.maugh@latimes.com