Background:
Syphilis incidence has increased dramatically in the United States since the mid-1990s, occurring primarily among men who have sex with men (MSM) and disproportionately affecting those with HIV infection. Despite ongoing public health efforts, syphilis infection rates among MSM have persisted, signaling the need for new prevention strategies.

Objective:
Our study aimed to examine the rate of repeat syphilis infection in San Francisco and to identify risk factors associated with syphilis re-infection that may inform additional secondary prevention strategies.

Method:
We developed a retrospective cohort of all cases of primary and secondary syphilis diagnosed in San Francisco in 2001 and 2002. We evaluated data through the end of 2003 to determine all cases of syphilis re-infection, defined as a new infection that occurred within one year following treatment of a prior infection. Syphilis infection was identified by rapid plasma reagin (RPR) or Venereal Disease Research Laboratory (VDRL) assays and confirmed by treponemal specific particle agglutination (TP-PA). Confirmed reactive titers were compared to a patient's previous syphilis history to identify a repeat infection.

Result:
We found that 5.9% (43/723) of cases had a repeat syphilis infection within one year. HIV infection was associated with an increased risk of repeat syphilis infection (OR= 4.7; CI 2.0-11.0), which remained significant when adjusted for sexual orientation (OR=1.4; CI 1.2-1.6). No differences in gender, age, race, number of sexual partners, illicit drug use, or partner meeting venues were observed between cases with and without repeat infections.

Conclusion:
Our study reveals that HIV-infected patients with syphilis represent an at-risk group for repeat syphilis infection.

Implications:
Our findings support current CDC recommendations for routine syphilis screening in all sexually active HIV-positive individuals and indicate that HIV-infected patients with syphilis merit targeted public health interventions to reduce the overall incidence of syphilis in this population.