Association of biological false-positive reactions for syphilis with human immunodeficiency virus infection

The prevalence of biologic false-positive (BFP) reactions for syphilis (reactive rapid plasma reagin [RPR) test, nonreactive fluorescent treponemal antibody absorption [FTA-ABS) test) among patients attending two sexuallytransmitted disease (STD) clinicswasevaluated to assess relationships between BFP reactions and human immunodeficiency virus (HIV) infection. Among 4863 patients, 357 (7.3%)had serologicevidenceof syphilisand 4.9%had HIV infection. Only 40 patients (0.8 % of total patients, 11 % ofthose with reactive RPR tests) had BFP sero-logic tests for syphilis. There were no demographic differences between true syphilis and BFP patients as to sex, age, or intravenous drug use. BFP patients tended to have lower RPR titers (";1:4) than did true syphilispatients. After excluding317 patients with reactiveFTA-ABStests, BFP RPR tests were seen in 6 (4%) of 159 HIV-seropositive patients and 34 (0.8%) of 4387 HIV-seronegative patients (odds ratio, 5.0; 95 % confidence interval, 1.9-12.7). Although more common among HIV-infected than HIV-uninfected patients, BFP reactions are relatively rare among STD clinic patients, and 89 % of patients with reactiveRPR or VDRL serologic tests for syphilishad current or prior syphilisinfection.The RPR test remains usefulfor guidingdecisions regarding therapy for syphilis