ORIGINAL STUDY Syphilis Testing Behavior Following Diagnosis With Early Syphilis Among Men Who Have Sex With Men—San Francisco, 2005–2008 Julia L. Marcus, MPH,* Kenneth A. Katz, MD, MSc, MSCE,† Kyle T. Bernstein, PHD, ScM,* Giuliano Nieri, BA,* and Susan S. Philip, MD, MPH* Background: In San Francisco, men who have sex with men (MSM) with early syphilis are at high risk of reinfection. We described syphilis testing behavior among MSM after diagnosis, identified factors associated with not testing, and developed algorithms to identify nontesters. Methods: We used syphilis surveillance data from 2005 through 2008 to describe follow-up testing behavior among MSM with early syphilis and titers of nontreponemal serologic tests 1:16. We ana- lyzed data from contact-tracing interviews to identify factors associated with not testing during the 1 to 6 months postdiagnosis. We developed and applied a multivariate model in a derivation set (2005–2006) and a validation set (2007–2008), respectively, calculating correct classifica- tion rates (CCR) to assess predictive ability and evaluating patient characteristics for potential interventions. Results: Among 795 MSM, 260 (33%) did not have a follow-up syphilis test. Not testing was associated with being HIV-uninfected (risk ratio [RR]: 1.9, 95% confidence interval [CI]: 1.5–2.6), residing outside of San Francisco’s gay-identified neighborhood (RR: 1.7, 95% CI: 1.0 –2.9), and being diagnosed at the municipal sexually transmitted disease clinic (RR: 1.5, 95% CI: 1.2–2.0) (CCR derivation set, 71.6%; CCR validation set, 71.3%). An intervention focusing on MSM with those 3 characteristics would include 13% of syphilis cases among MSM and identify 26% of nontesters. Conclusions: Although MSM in San Francisco are at high risk for syphilis reinfection, one-third of MSM diagnosed with syphilis did not test during the 1 to 6 months postdiagnosis. Interventions to encourage follow-up testing among persons with syphilis might contribute to more effective syphilis prevention and control efforts. A fter reaching a historic nadir in 2000, the incidence of primary and secondary (P&S) syphilis in the United States increased annually through 2008. 1 That increase has been con- centrated primarily among men who have sex with men (MSM), who accounted for 63% of P&S cases in 2008. A large proportion of MSM infected with P&S syphilis are coinfected with human immunodeficiency virus (HIV). 2–5 In San Francisco, reported cases of P&S syphilis increased 67% from 2007 (n = 204) to 2008 (n = 342). 6 More than 90% of cases during 2008 were among MSM, of whom 64% were coinfected with HIV. Persons who are reinfected with sexually transmitted diseases (STDs) have been considered to comprise a core group that might sustain transmission in a population 7 ; thus, interven- tions that focus on this group might reduce local community burden of disease. Whereas several studies have examined reinfection with Neisseria gonorrhoeae and Chlamydia tracho- matis, 8 –12 few have explored repeat syphilis. Because syphilis is relatively rare, persons who are reinfected with syphilis might be more likely to disproportionately sustain endemic transmission than persons who are reinfected with N. gonor- rhoeae or C. trachomatis. A study of early syphilis among MSM in San Francisco found that 6.7% of patients had a newly diagnosed syphilis infection within 1 year of diagnosis and treatment. 13 Others have reported rates of syphilis reinfection of 10% within 10 years in British Columbia, 14 17.6% within 17 years in Seattle 15 and 42.7% within 1 year in Peru. 16 The San Francisco Department of Public Health (SFDPH) recommends that sexually active MSM have a serologic test for syphilis every 3 to 6 months, and that persons diagnosed with syphilis have a serologic test for syphilis at 1, 3, 6, 9, and 12 months after diagnosis. 17 Serologic testing of syphilis patients after diagnosis allows for clinical follow-up to monitor post- treatment titer decline and can identify treatment failures and new cases. Despite guidelines on screening and follow-up testing for healthcare providers, and social marketing cam- paigns to promote syphilis testing among MSM, 18,19 syphilis incidence has remained high among MSM in San Francisco since 2002, 6 with increased rates of infection among persons who have previously been infected. 13 Because MSM diagnosed with syphilis are more likely to acquire syphilis in the future compared with MSM not diagnosed with syphilis, it is critical that MSM diagnosed with syphilis regularly test for syphilis after they are diagnosed. Follow-up testing is important clinically because it can detect treatment failure, but treatment failure is rare. Follow-up test- ing is even more critical from a public health perspective because it can detect, as early as possible, new cases of syphilis in a population at high risk of syphilis. Therefore, our objective in this study was to describe and analyze syphilis testing behavior among those MSM who were previously infected with syphilis. Specifically, we aimed to describe syphilis testing behavior following diagnosis with early syphilis among MSM in San Francisco, to identify factors associated with not having a syphilis test following diagnosis, and to develop algorithms to From the *San Francisco Department of Public Health, San Francisco, CA; and †Health and Human Services Agency, County of San Diego, San Diego, CA The authors thank the disease investigation team at the San Francisco municipal STD clinic, City Clinic, for conducting syphilis inter- views: Rosito Bartolini, Anna Branzuela, Gloria Calero, Christo- pher Fox, Luis Hernandez, James McMaster, Sharon Penn, and Rebecca Shaw. Supported by Comprehensive STD Prevention Projects (1H25PS001354 – 01), Centers for Disease Control and Prevention. Correspondence: Julia L. Marcus, MPH, STD Prevention and Control Services, San Francisco Department of Public Health, 1360 Mission St, Suite 401, San Francisco, CA 94103. E-mail: julia.marcus@sfdph. org. Received for publication January 20, 2010, and accepted May 25, 2010. DOI: 10.1097/OLQ.0b013e3181ea170b Copyright © 2010 American Sexually Transmitted Diseases Association All rights reserved. Sexually Transmitted Diseases ● Volume 37, Number 12, December 2010 1