Background:
Syphilis increases were first reported in gay men and other men who have sex with men (G/MSM) in San Francisco in 1999. Additional reports followed of similar increases in syphilis in G/MSM worldwide.

Objective:
To describe the epidemiology of primary and secondary syphilis in San Francisco from 1999 to 2007 and identify factors which may have been associated with recent declines.

Method:
We reviewed reported cases of primary and secondary syphilis from 1999 to 2007. We reviewed a variety of interventions to mobilize the community, increase provider and public education about syphilis, expand clinical prevention and treatment services including partner notification, increase routine syphilis testing in persons at high risk for syphilis and regular evaluation and surveillance. In addition, we reviewed efforts to identify and abate risk factors associated with incident syphilis cases. We defined recent syphilis test as test in prior 6 months.

Result:
After an increase from 29 cases in 1999 to 349 cases in 2004, primary and secondary syphilis cases decreased to 249 in 2005, 243 and 2006 and an estimated 185 cases in 2007, a 47% decrease from the 2004 peak. Multiple interventions were initiated during the outbreak period. A large increase was observed in the population-level frequency of routine syphilis testing from an estimated less than 10% of G/MSM getting a recent syphilis test in 1999 to more than 70% of HIV-infected and 50% of HIV-uninfected reporting a recent syphilis test in 2007.

Conclusion:
Syphilis incidence has substantially declined in San Francisco. Multiple interventions were implemented. A large and sustained increase in the proportion and frequency of syphilis testing in the target population was observed.

Implications:
Understanding an effective response to syphilis increases can help local health departments prioritize interventions and use limited resources judiciously