Oct. 2 (Bloomberg) -- The number of people infected with the AIDS virus, HIV, increased 11 percent in the U.S. from 2003 to 2006 as better treatments have prolonged their lives, government researchers said.

The HIV-infected population rose to 1.1 million in 2006 from an estimated 994,000 in 2003, scientists at the Centers for Disease Control and Prevention said in a study to be published tomorrow in the agency's Morbidity and Mortality Weekly Report.

Since combinations of powerful drugs were introduced in 1996, the average life expectancy of 20-year-old HIV patients has risen about 13 years, scientists said in the medical journal Lancet in July. The estimate also reflects CDC's recent study that raised its count of annual new infections by about 40 percent to more than 56,000, the Atlanta-based agency said.

CDC expects HIV cases ``to keep on increasing over time as treatment prolongs the lives of infected people and new infections outpace deaths,'' said Richard Wolitski, acting director of CDC's Division of HIV/AIDS Prevention, today in a telephone interview.

Blacks were the hardest hit racial group, accounting for about 46 percent of cases in 2006. About 1.7 percent of U.S. blacks are infected, compared with 0.6 percent of Hispanics and 0.2 percent of whites.

``CDC has recognized and reported data on the disproportionate impact of the disease on blacks in the U.S. since the early years of the epidemic,'' Wolitski said. ``This disparity is not one that is new, but it's one that remains and requires a heightened level of response.''

Testing Urged

The agency has also pushed HIV testing to encourage infected people to begin life-saving treatment programs and make them aware of the risk of spreading the infection, Wolitski said. About half of new infections originate from people who have the virus and don't know it, according to the CDC.

About half of all patients were men having sex with men, or MSM, the study said. About 18 percent of people contracted the virus by injecting drugs with contaminated needles.

``Expanding the number and reach of effective HIV prevention services for at-risk populations, including blacks, Hispanics, and MSM of all races, can contribute to reducing the disproportionate numbers of infections in these groups,'' the authors concluded.

About 33 million people are infected with HIV worldwide with 2.7 million new infections last year, according to a July 29 report by UNAIDS, the New York-based agency that coordinates the United Nations response to the disease. The number of deaths dropped about 10 percent to 2 million in 2007 because of increased availability of drugs, the report said.

To contact the reporter on this story: John Lauerman in Boston at jlauerman@bloomberg.net.

Last Updated: October 2, 2008 15:50 EDT