Hepatitis C virus infection and biological false-positive syphilis tests

Background: The diagnosis of syphilis requires two-step serological testing. Not infrequently, sensitive screening tests are reactive but are not confirmed by more specific confirmatory tests yielding a biological false positive (BFP). This study sought to describe the prevalence of BFP in a large population of hepatitis C virus (HCV)-infected and uninfected women. Methods: A cross-sectional serosurvey of HIVseropositive and HIV-seronegative women enrolled in the Women's Interagency HIV Study, a multicentre collaborative study of the natural history of HIV in women. Results: Among HCV-infected women 4% had a BFP compared with 1% among those who were HCV uninfected (odds ratio (OR) 3.3, 95% CI 2.1 to 5.1). Controlling for both HIV infection and a history of intravenous drug use among all tests for syphilis a BFP also occurred more commonly in HCV-infected women compared with HCV-uninfected women (6% vs 1%, OR 7.62, 95% CI 1.9 to 12.5). Conclusion: HCV infection is associated with various effects on immune function including alterations in serological test results. Women with HCV are more likely to have a BFP syphilis test than women without HCV.