Enzyme linked immunosorbent assays with Treponema pallidum or axial filament of T phagedenis biotype Reiter as antigen: evaluation as screening tests for syphilis.

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Abstract
Enzyme linked immunosorbent assays with an ultrasonicate of Treponema pallidum (TP-ELISA) or axial filament of Treponema phagedenis biotype Reiter (AF-ELISA) were developed to detect treponemal antibody. TP-ELISA and AF-ELISA were compared with the T pallidum haemagglutination assay (TPHA), the fluorescent treponemal antibody-absorbed (FTA-ABS) test, and the Venereal Disease Research Laboratory (VDRL) test for sensitivity and specificity of serodiagnosis of syphilis. A total of 1423 serum samples, 253 from patients with various stages of syphilis, 500 from patients attending a sexually transmitted disease (STD) clinic, and 670 from people without syphilis, were investigated. At all stages of syphilis the sensitivity of the TP-ELISA, the AF-ELISA, the TPHA, and the FTA-ABS test did not differ significantly, except that the AF-ELISA was less sensitive than the TPHA (p less than 0.05) for treated syphilis. In primary syphilis, neurosyphilis, and treated syphilis the TP-ELISA and AF-ELISA were significantly more sensitive than the VDRL test (p less than 0.05). The specificity of all tests was comparable (p greater than 0.05). The TP-ELISA and AF-ELISA appear to be good alternatives to the TPHA as screening tests for syphilis. Because of the easy availability of a well defined antigen the AF-ELISA seems to be better suited for large scale testing.