Treponema pallidumSurface Immunofluorescence Assay for Serologic Diagnosis of Syphilis

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Abstract
A surface immunofluorescence assay (SIFA) using live spirochetes was analyzed and compared with Western blot (WB), fluorescent treponemal antibody absorption (FTA-ABS), microhemagglutination (MHA-TP), andTreponema pallidumimmobilization (TPI) assays for detecting serum antibodies toT. pallidumin patients with syphilis, in disease controls, and in healthy subjects. SIFA and WB were 99% sensitive (99 of 100 positive specimens) and specific (140 of 140 negative specimens); FTA-ABS showed a sensitivity and a specificity of 90 and 89% (90 of 100 positive and 125 of 140 negative specimens), respectively. MHA-TP showed a sensitivity of 84% (84 of 100 positive specimens) and a specificity of 98.5% (138 of 140 negative specimens). Finally, TPI had a sensitivity of 52% (52 of 100 positive specimens) and a specificity of 100% (140 of 140 negative specimens). TheT. pallidumSIFA was therefore highly specific, showing no equivocal reactivities with control sera, and sensitive. The results suggest the possible use of SIFA as a confirmatory test in the serologic diagnosis of syphilis.