NEW YORK (Reuters Health) - The rate of new HIV cases in gay and bisexual men may have dropped in California in the mid-2000's, suggests a new study published 30 years after the discovery of the virus that causes AIDS.
Still, the rates of new, positive HIV tests in recent years were highest in men age 18 to 24, a finding that suggests younger men may be more likely to engage in risky behaviors such as unprotected sex, researchers say.
"We now have pretty clear evidence that the fact that people have lower viral loads and more and more are on treatment means that there's less transmission" of HIV, said Pamina Gorbach, an epidemiologist who studies risk behavior and HIV at the University of California, Los Angeles.
While this research is not the first to hint at a shrinking rate of new HIV cases in gay and bisexual California men, "it'll be interesting to see if the pattern is the same in terms of a continuing downward trend," Gorbach, who was not involved in the new study, told Reuters Health.
The Centers for Disease Control and Prevention estimates that more than 1 million people in the United States have HIV.
Led by Dr. Qiang Xia, then at Research Triangle Institute International, in Research Triangle Park, North Carolina, the researchers calculated rates of new HIV-positive diagnoses at counseling and testing sites run by the California Department of Public Health.
Their study included all gay and bisexual men who had at least one test at those sites between 1997 and 2007 after a prior negative HIV test. Xia, now at the New York City Department of Health and Mental Hygiene, and her co-authors organized the data to account for the effect of HIV testing campaigns in California on the number of men being tested, and to adjust for the fact that some men were tested multiple times during those years.
They included data from as many as 18,000 men per year.
Rates of new annual diagnoses of HIV increased from 2 percent of men in 1997 to 2.4 percent in 2003. Then, the rate fell back to 1.9 percent in 2006 according to the data, presented in the American Journal of Epidemiology.
In particular, rates of new annual diagnoses in African American men dropped from 4.8 percent to 2.3 percent over the course of the study period.
Despite that trend, Xia and colleagues wrote that it was "concerning" that in the later years of the study, men age 18 to 24 had the highest rate of new HIV diagnoses - 2.9 percent in 2006.
Young people, as well as minorities, "are the groups that are hardest to reach," Gorbach said. "But as we expand our program and use new methods of prevention and new approaches, I think we'll do a better job with these groups."
The authors point out that because they only looked at one group of testing sites, their data may not show the actual rates of new HIV cases in the whole state. But the trends, they say, may reflect how the frequency of the virus is changing among gay and bisexual men in California.
Susan Scheer, who studies HIV at the San Francisco Department of Public Health, said that the downward trend is probably the result of more people knowing their HIV status and being less likely to pass on the virus if they do have it.
"The time between tests is decreasing," Scheer, who was also not part of the new research, told Reuters Health. "That's really been a big push, especially in recent years -- to get more people tested more often. I think that's probably a big part of it, (and) we do see really high rates of treatment among people who are positive."
"When all those things come together, (people with HIV) are less likely to transmit infection," she added.
Gorbach said that in California, the HIV epidemic is "very concentrated" among gay and bisexual men, and that it may take a little longer to see a drop in new HIV diagnoses among other groups.
She also thinks the trend will eventually be visible on a nationwide scale, as more people with the virus are taking antiretroviral drugs and have less of the active virus in their blood.
However, Gorbach said one thing that hasn't changed much is that many people are still engaging in risky behavior that increases their chance of getting HIV. And Scheer added that many Americans still aren't getting tested for the virus, which is why about a quarter of people across the country who are infected don't know it, she said.
Still, Gorbach said, "I think it's a great time to be optimistic about prevention."
SOURCE: bit.ly/kmmAsp American Journal of Epidemiology, online May 17, 2011.