Officials analyze
reasons behind San Francisco’s falling HIV rate

Health officials in San Francisco are analyzing data in a recent federal Centers for Disease Control and Prevention report showing that the HIV incidence level has been cut nearly in half among gay and bisexual men in the city, to determine exactly why the drop-off in new infections occurred, The New York Times reports. The study, based on a survey of gay men tested for HIV, showed the annual incidence rate dropped from 2.2% to 1.2%. Separate data collected by the Stop AIDS Project and surveys conducted in city health clinics also suggest new HIV infections are declining among gay men.

"We interpret this CDC report as good news, and there are some other encouraging trends and results of other studies," Willi McFarland, director of the city health department's HIV seroepidemiology unit, told the Times. "But we definitely do need to corroborate and independently confirm any decrease in HIV incidence by carefully examining other data. We also need to figure out if this is true, then why."

Health officials believe much of the reason for the declining HIV rates may be due to "serosorting"--through which gay men seek and have sex only with other men of the same HIV serostatus. If HIV-positive men are largely having sex only with other men who are already infected, fewer HIV-negative men are being exposed to the virus, they say.

"Studies have shown, when people have knowledge of their serostatus, they take that knowledge and use it to protect their partners," Patrick Sullivan, chief of CDC's behavioral and clinical surveillance branch, told the Times. "Serosorting is one piece of that whole benefit that arises from people learning their status through HIV testing."

Successful antiretroviral therapy also may be playing a role in lowering HIV infection rates by dramatically decreasing viral levels in the bodies of HIV-positive people and making them less likely to pass the virus along to others through unprotected sex, researchers say. Health officials also believe that educational meetings and workshops, efforts to boost HIV testing among gay men, and harm-reduction strategies for crystal methamphetamine users could be impacting HIV infection rates.