EPIDEMIOLOGY AND SOCIAL SCIENCE HIV Incidence Among Men Diagnosed With Early Syphilis in Atlanta, San Francisco, and Los Angeles, 2004 to 2005 Kate Buchacz, PhD, MPH,* Jeffrey D. Klausner, MD, MPH,† Peter R. Kerndt, MD, MPH,‡ R. Luke Shouse, MD, MPH,§ Ida Onorato, MD,* Peter D. McElroy, PhD, MPH,* Joseph Schwendemann, BS, k Pradnya B. Tambe, MD,¶ Michelle Allen, BA,¶ Frank Coye, MA,# Charlotte K. Kent, PhD, MPH,† Mahin N. Park, PhD,** Kellie Hawkins, MPH,‡ Erika Samoff, PhD, MPH,†† and John T. Brooks, MD* Background: Syphilis outbreaks among men who have sex with men (MSM) in the United States have raised concerns about increased HIV transmission in this population. We sought to estimate HIV incidence among men diagnosed with primary or secondary (P&S) syphilis in sexually transmitted disease (STD) clinics in Atlanta, San Francisco, and Los Angeles. Methods: We analyzed deidentified sociodemographic informa- tion from routine syphilis surveillance databases and matching remnant sera from consecutive male patients with P&S syphilis who were tested for syphilis at 3 public health laboratories during January 2004 through January 2006. Deidentified sera positive for Treponema pallidum by particle agglutination were screened for HIV-1 antibodies by enzyme immunoassay (EIA). Specimens that were confirmed HIV- positive by Western blot analysis were then tested for recent HIV infection using the less sensitive (LS) HIV-1 Vironostika EIA and BED HIV-specific IgG/total IgG assay. Results: Of 357 men with P&S syphilis (98 in Atlanta, 151 in San Francisco, and 108 in Los Angeles), 32% had primary syphilis and 85% were MSM (12% no MSM risk and 3% no information). The median age was 36 years; 40% were white, 31% black, 20% Hispanic, and 8% other. Among men with P&S syphilis, 160 (45%) were HIV-positive, of whom 8 were classified as having acquired recent HIV infection by the LS-Vironostika EIA (all confirmed by BED) and had no history of antiretroviral use or HIV-positive results .6 months earlier. Seven of the 8 men with recent HIV infection were MSM. The estimated HIV incidence was 9.5% per year (95% confidence interval [CI]: 2.9 to 16.0) among all men and 10.5% per year (95% CI: 2.7 to 18.3) among MSM. Conclusions: We found high HIV incidence among a high-risk population of US men diagnosed with P&S syphilis in STD clinics in Atlanta, San Francisco, and Los Angeles. Intensive integrated HIV/STD prevention programs are needed for this population. Key Words: BED, HIV incidence, men who have sex with men, serologic testing algorithm for recent HIV seroconversion, syphilis (J Acquir Immune Defic Syndr 2008;47:234–240) S ince 1998, outbreaks of syphilis among men who have sex with men (MSM) have been documented in numerous US cities 1–6 and internationally 7–10 and have raised concerns about increased HIV transmission in this population. Approximately 50% to 60% of newly identified primary and secondary (P&S) syphilis infections among MSM in these cities are among persons already known to be HIV-infected. 1–5 Syphilis infection facilitates acquisition and transmission of HIV infection, 11–15 and possible increases in sexual risk behavior accompanying the outbreaks of syphilis 16,17 may also contribute to sustained or increasing HIV incidence among MSM. Preliminary studies using the sensitive/less sensitive (LS) enzyme immunoassay (EIA) testing strategy (also known as the serologic testing algorithm for recent HIV seroconversion [STARHS]) 18 have documented high HIV incidence in men diagnosed with early syphilis. Among 74 men who were diagnosed with P&S syphilis at the San Francisco municipal sexually transmitted disease (STD) clinic during 2002 to 2003 and who accepted confidential HIV testing, estimated HIV incidence was 13.9% per year (95% confidence interval [CI]: 0.3 to 27.5). 19 A study of anonymous sera from 212 men with early syphilis diagnosed in STD clinics and other public sites in Los Angeles County during 2002 to 2004 estimated HIV incidence at 17.0% per year (95% CI: 12.0 to 22.0). 20 These 2 studies provide relatively imprecise estimates of incidence, and their validity may be affected, respectively, by potential volunteer bias and by misclassification of incident HIV cases because of limited HIV testing history information. However, these preliminary findings suggest frequent HIV transmission in Received for publication April 12, 2007; accepted October 12, 2007. From the *Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, Atlanta, GA; †STD Prevention and Control Services, San Francisco Department of Public Health, San Francisco, CA; ‡STD Program, Los Angeles County Department of Health Services, Los Angeles, CA; §Georgia Division of Public Health, Atlanta, GA; k The New York State Diagnostic HIV Laboratory, Albany, NY; {Fulton County Department of Health and Wellness, Atlanta, GA; #Dekalb County Board of Health, Atlanta, GA; **Georgia Public Health Laboratories, Decatur, GA; and the ††Division of STD Prevention, Centers for Disease Control and Prevention, Atlanta, GA. I. Onorato is deceased. The findings and conclusions from this report are those of the authors and do not necessarily represent the views of the Centers for Disease Control and Prevention. Correspondence to: Kate Buchacz, PhD, Division of HIV/AIDS Prevention, Centers for Disease Control and Prevention, 1600 Clifton Road, NE, Mailstop E-45, Atlanta, GA 30333 (e-mail: acu7@cdc.gov). Copyright Ó 2007 by Lippincott Williams & Wilkins 234 J Acquir Immune Defic Syndr  Volume 47, Number 2, February 1, 2008 Copyright © 2008 Lippincott Williams & Wilkins. Unauthorized reproduction of this article is prohibited.