THURSDAY, Jan. 19 (HealthDay News) -- The number of Americans who practice behaviors that put them at risk for HIV infection has declined significantly, federal health officials reported Thursday.

The ranks of those engaging in a risky sexual or drug-related behavior dropped from 13 percent of men and 11 percent of women in 2002 to 10 percent and 8 percent, respectively, in 2010, according to the U.S. Centers for Disease Control and Prevention.

"Generally, these are behaviors that are studied in higher risk populations, but by looking in the household population we can get a better sense of the level of risk that may exist in the general population that you don't normally think about," said report author Anjani Chandra, a health scientist at the CDC's National Center for Health Statistics.

Some of the risk factors the researchers looked at were gay and bisexual sex, illicit drug use and having several sexual partners or a partner who injects illegal drugs, she said.

"For women, we don't really see that the decline is due to any variation in sexual risk behaviors, whereas for men we see substantial difference by race," she said.

The reasons for the decline in risk behaviors is not clear, Chandra said. Some of the public health messages might be getting through. It also could be that people are reluctant to disclose that they engage in risky behaviors, she said.

"But, it could be real and reflect actual changes in behavior," she said.

The data in the report was collected on almost 23,000 men and women aged 15 to 44 in households throughout the country and represents 6.5 million men and 4.9 million women.

The decline seems to be due to a drop in risky behaviors such as having unprotected sex and having sex with multiple partners, Chandra said.

There were, however, differences in behaviors in different groups. For example, men who had recently been in prison were more likely to report engaging in one or more HIV risk behaviors, compared with other men, the researchers found.

There were also significant variations based on race and income level, they reported.

Sixteen percent of young black men ages 15 to 24 reported at least one HIV risk-related sexual behavior, compared with 8.7 percent of Hispanic men and 6.5 percent of young white men. Poorer men were also more likely to engage in risky behaviors.

The HIV risk in households is not something one usually thinks about when one thinks about HIV risk, Chandra said.

"In household populations, where you may think these behaviors are nonexistent or very rare, they are occurring and they may be placing people at risk of HIV and other sexually transmitted diseases," Chandra said. "Just focusing on high-risk populations may not take care of the concerns that we have."

Dr. Sten Vermund, director of the Institute of Global Health at Vanderbilt University School of Medicine in Nashville, said that the data used was "a highly valid sample of the American population."

Both sexual and drug-related risk behaviors declined in the study period, and that is a positive trend, he said.

"Risk behaviors remain high and the likelihood of encountering an HIV-infected person has never been higher," Vermund noted. "Nonetheless, there is a strong indication that prevention programs are working or cultural norms are shifting, or both."

Philip Alcabes, an associate professor in the School of Health Sciences at Hunter College/City University of New York, is critical of the report as another example of how the government still avoids the real problem of HIV.

"What a waste of time and taxpayer dollars," he said. "Having failed to advocate for structural changes that would actually reduce risk of HIV acquisition and having failed to implement widespread, easily accessible syringe exchange programs, federal agencies instead spend their time studying personal behavior. It's a shame."

"Even though our officials don't have a clear concept of what really happened 30 years ago, they are still looking at AIDS through the same moralizing lens that was common in 1981. That's sad, and disturbing," he said.

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