Evaluation of a Treponema pallidum enzyme immunoassay as a screening test for syphilis

The CAPTIA Syphilis-G enzyme immunoassay for the detection of antibodies to Treponema pallidum was evaluated as a screening test for syphilis in comparison with the standard rapid plasma reagin (RPR) test. One thousand samples were tested, and the standard fluorescent treponemal antibody absorption test and the standard microhemmaglutination test were used to confirm the presence of treponemal antibodies. Diagnosis of syphilis was based on traditional standard serology results. Clinical data used in the diagnosis of patients whose samples yielded conflicting results were provided by physicians. Initially, 7 patients whose samples were reactive in the RPR test and 14 patients whose samples yielded positive or equivocal results in the CAPTIA Syphilis-G test were diagnosed as not being infected. After discrepancies due to technical problems were reconciled, samples from six patients remained reactive in the RPR test and that from one patient remained positive in the CAPTIA Syphilis-G test. In addition, seven patients whose samples were nonreactive in the RPR test and two patients whose samples were negative in the CAPTIA Syphilis-G test were diagnosed as having untreated syphilis. After discrepancies were reconciled, samples from five patients remained nonreactive in the RPR test and none remained negative in the CAPTIA Syphilis-G test. Final results indicate that the specificities are 99.4 and 99.9%, respectively. In addition to the improved sensitivity and specificity of the CAPTIA Syphilis-G screen, other potential benefits of this assay lead us to believe that this method could serve as a better screening tool than the RPR test.