False-positive tests for syphilis associated with human immunodeficiency virus and hepatitis B virus infection among intravenous drug abusers

The role of HIV, hepatitis C virus, and hepatitis B virus infections in the production of biological false-positive reactions for syphilis was evaluat ed in two large samples of intravenous drug abusers and homosexual men atte nding AIDS prevention centers in Spain. A significantly increased odds rati o (OR) for false-positive tests for syphilis [OR 2.23, 95% confidence inter vals (CI) 1.76-2.83] was observed for HIV seropositive intravenous drug abu sers; biological false-positive reactions were also more frequent (OR 1.73, 95% CI 1.30-2.31) among intravenous drug abusers who were hepatitis B viru s seropositive but not among those who were hepatitis C virus seropositive (OR 0.90; 95% CI 0.48-1.69). Among homosexuals, the association between HIV and biological false-positive reactions was restricted to subjects who wer e also intravenous drug abusers, indicating the crucial role of intravenous drug abuse. Only 20.5% of intravenous drug abusers with a previous biologi cal false-positive reaction yielded a false-positive result in their subseq uent visit.