New York Times - August 18, 2005
Dean E. Murphy

But the gathering last week at a coffee shop in the largely gay Castro district was not a casual pickup session. The dozen or so men were infected with the virus that causes AIDS, and the talk was of "responsible sex," not through condoms, necessarily, but through choosing sex partners who are already infected.

"I don't think I could sleep at night if I knew I had infected another human being," said one of the men, Don Stewart, who tested positive for HIV five years ago.

The monthly social event, called Positive Space and organized by an AIDS prevention group, is among the scores of educational meetings, workshops, seminars and parties that health officials here say are contributing to a significant decline in the incidence of HIV among gay men in San Francisco.

The Centers for Disease Control and Prevention estimated in a report in June that new infections in San Francisco among men who have sex with men were occurring at about half the rate previously calculated by city health officials - 1.2 percent per year instead of 2.2 percent.

That is the lowest rate reported in San Francisco since 1997 and the lowest among five cities with significant gay populations studied by the federal agency.

Since the report's release, health officials here, known for their cautious approach to shifts in AIDS trends, have been scrambling to confirm the results and offer an explanation for the good news. Some officials have said that the decline has been fueled by conventional efforts like stepped-up HIV treatment programs, easier and more regular tests and so-called harm-reduction strategies like discouraging the use of crystal methamphetamine, a drug blamed for helping to spread the disease by lowering inhibitions.

But other signs, like the proliferation of matchmaking Web sites for HIV-infected men and the relatively high number of men here who know their HIV status, point to a growth in the number of men looking for partners with the same status. The practice is known as sero-sorting, which involves men choosing sex partners based on their common serostatus, a term that refers to the presence of antibodies to a particular infectious agent in the blood.

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

Since the AIDS epidemic began nearly 25 years ago, San Francisco has often been a laboratory of sorts, with many behavioral changes, both good and bad, occurring here before spreading to other cities.

Though the disease control centers' report is just one in a sea of statistical analyses and studies about HIV, containing the usual caveats about possible reporting errors and potentially skewed sampling, the emerging consensus in San Francisco is that the new numbers signal a reversal in a sharp rise in infections that began about seven years ago.

"When I first saw the data, I was skeptical and had to be convinced," said Jeff Sheehy, an adviser on AIDS issues to Mayor Gavin Newsom of San Francisco. "There's a lot of fortunate events coming together to drive this. It's incredibly important to start people really looking at the factors driving the downward trend and reinforce and encourage those factors."

050818
NYT050812