While HIV is experiencing downward trends — due to improved prevention, testing, and treatment — the San Francisco Department of Public Health is struggling against alarming increases in transmission of other sexually transmitted diseases, especially syphilis.

Susan Philip, director of STD Prevention and Control Services, says the prevalence of these diseases is the "failure of traditional public health approaches to controlling STDs nationally and internationally." Their inability to counter new outbreaks is even more infuriating in regard to syphilis, which has a multi-week incubation period. "If we could identify and treat syphilis within that first window — before the initial lesion — then we should be able to stop the cycle of transmission."

Optimism reigned in 1999 — syphilis cases were so low that the Centers for Disease Control believed they were on the cusp of eradicating it — but since 2000, there's been a sustained increase every year.

Along with gonorrhea and chlamydia, syphilis is occurring in higher numbers among homosexual men and transgender persons. Researchers have suggested a number of causes, but suspect the reasons are hidden in the data. For example, a large portion of STD cases occurred among people who met their partners on the Internet, but even this is complicated by possible red herrings.

"Everyone is on OKCupid these days," says Kyle Bernstein, chief of epidemiology at SFDPH. "If there's an overall increase of users on the Internet, it could be a misleading connection; more people are just online these days."

Another piece of the equation is that many syphilis symptoms are painless, unlike more "vocal" STDs like urethral gonorrhea.

Both the CDC and SFDPH have also considered less obvious reasons for the increase, like the "stigma and homophobia that discourage people from getting tested or notifying partners," says Philip. "These elements are difficult to measure, but are definite determinants of health." The search for answers is made more urgent by the fact that people infected with syphilis are more likely to both transmit and receive HIV.

So despite improvements in treatment, knowledge, and outreach, the past 13 years have been an uphill battle.

"We're using a multi-pronged approach, but everybody is struggling with how to improve the health of this disproportionately affected population," Philip says. "It's not a matter of opening another clinic — we have to reduce barriers to screening.

While the current epidemic is affecting the gay and transgender populations in S.F., Philip points out that STDs have historically affected different populations at different times, including minority groups and drug users. Which means more data to sift through.

"We can't keep doing the same things we've always done and wonder why things aren't improving," she says. "We're taking a new holistic approach that looks at the entire person. It's a brave new world."