In the new report, published in the July 23/30 issue of the Journal of the American Medical Association, researchers examined HIV diagnoses in the United States from 2002 to 2011 in people aged 13 and older.
Although almost 500,000 people were diagnosed with HIV during that time, the annual rate of diagnoses fell from 24 out of every 100,000 people to 16 -- a decline of 33 percent.
Many groups experienced significant declines in infection.
Among women, diagnosis rates dropped by about half, and among men by more than one-quarter. For blacks and Hispanics, the rates of diagnosis declined 37 percent and 41 percent, respectively.
The report estimates that HIV infections due to injection drug use fell by roughly 70 percent and from heterosexual contact by more than one-third for men and women.
Distribution of sterile needles, increased HIV testing and drug-treatment programs could explain some of the downward trend, Lansky said.
But the diagnosis rate jumped among males aged 13 to 24, suggesting that many gay and bisexual young men aren't using condoms during sex. The number of newly diagnosed cases in that age group rose from about 3,000 to about 7,000, Lansky said.
"The increases tell us where we need to keep putting our efforts," Lansky said. "To build on the progress that we've made, we're really starting to focus on those who are in greatest need."
Dr. David Margolis, an AIDS specialist at the University of North Carolina at Chapel Hill, said one way to do that is to promote use of HIV drugs by people who are at risk but not infected. "Pre-exposure" treatment is controversial, however, because some experts fear it might encourage users to have more unprotected sex.
"The use of antivirals to prevent HIV infection is fraught with many challenges," Margolis said, "but if there is a more than doubling of new
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