SAN FRANCISCO (AP) — Aiming to stem an alarming rise in syphilis, San Francisco health officials are turning to the place where they say many infected residents meet their sexual partners: the Internet.

The Department of Public health launched a website this week where people who think they may have contracted syphilis can order confidential tests by printing out laboratory slips containing personal identification numbers instead of their names.

Once the potential patients have their blood drawn at a participating lab, their results will be posted online with the same nine-digit number.

“Nearly 40 percent of recent syphilis cases have met their sex partners online,” said Dr. Jeffrey Klausner, director of the department’s sexually transmitted diseases unit. “Now, we can offer these same Internet users a free, convenient way to access STD testing via the Web.”

Deb Levine, who works with an educational group called Internet Sexuality Information Services, cautioned that while the new site affords users an important measure of privacy, it is not strictly anonymous.

Via personal information visitors must enter before obtaining their ID numbers, those who test positive for syphilis will be contacted by the health department for mandatory counseling and follow-up, she said.

But that doesn’t eliminate the website’s value, said Levine, who is helping city officials spread word about the program.

“It reduces any kind of embarrassment of having to discuss this with your doctor. It reduces the time it would take to go to a public health clinic,” she said. Lastly, it gives you that privacy of finding out results online at home, where you don’t have to worry about bumping into somebody you know.”

The site, www.stdtest.org, is the latest weapon in Klausner’s crusade to protect San Francisco from what he sees as the very real side effects of “cybersex.” Four years ago, after tracing a small syphilis outbreak to gay men who participated in an America Outline chat room, he began a protracted, though ultimately successful effort to persuade AOL to publish health warnings and safe sex information in its chat rooms.

Since then, Klausner has found other avenues for getting his message out. A San Francisco-based Internet company, PlanetOut Partners, agreed to send trained volunteers into the chat rooms of its two gay-oriented web sites to talk about health issues and to post special alerts when spikes in new cases occurred. The health department ran a syphilis prevention campaign called “Healthy Penis 2002” that included displaying cartoon penises and syphilis sores on bus shelters and in gay clubs.

But the syphilis rate in San Francisco has continued to go up. Over 1,000 new cases have been diagnosed since 1999, when there were just 47 reported infections. Last year, there were 595 new cases, nearly double the number from the year before, and two-thirds of them were found in HIV positive men, raising fears that the syphilis epidemic presages a resurgence in HIV transmission.

Syphilis is a sexually transmitted disease that begins as a sore and develops into a rash. It can be treated with penicillin, but if left unaddressed can damage vital organs. It can also make those with the disease more susceptible to HIV.

Although some studies have shown that people who use chat rooms are more likely to have sexually transmitted diseases, Levine said no data exists showing men who meet online engage in riskier sex. At the same time, the anonymity the Internet affords makes it easier for people to find partners.

“People are willing to take risks online because there is no shame and embarrassment in it,” Levine said. “But it’s also this incredible place for education because people are willing to ask their questions without worrying about judgment.”

The city is hoping to stem the increase by having most HIV-positive residents routinely tested for syphilis. Klausner says the new site will be promoted at gay-oriented websites, through advertisements on buses, and with outreach at sex clubs and adult bookstores.