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Background: In December 2007, the Illinois Department of Public Health Laboratory replaced the non-treponemal rapid plasma reagin (RPR) test with the treponemal enzyme immunoassay (EIA) (Trep-Sure TM) as the initial diagnostic syphilis screening test. A positive EIA test is confirmed by an algorithm using the RPR and fluorescent treponemal antibody (FTA) tests.
Objectives: To summarize the clinical interpretations of discordant syphilis results from a high-morbidity LGBT STD Clinic.
Methods: All syphilis EIAs performed between January 2008 and June 2009 were analyzed. Discordant results were defined as discrepancies between EIA, RPR, and/or FTA results.
Results: Of the 3,608 EIAs performed, 382 (10.6%) were seroreactive and 151 (4.2%) were associated with new syphilis cases. Of the 22 clients with no history of syphilis and EIA+/RPR-/FTA- results, 17/22 (77%) were retested and obtained similar test results, ruling out early syphilis infection. We considered these false positive syphilis results. Nineteen asymptomatic clients without a history of syphilis were EIA+/RPR-/FTA+ and would have been missed by RPR screening alone. Four clients with symptoms of primary syphilis and no history of syphilis tested EIA negative. Confirmatory serological testing identified three clients with RPR+/FTA+ (all with RPR titer of 1:8) tests and one client with RPR-/FTA+ tests.
Conclusions: Retesting clients with no history who were EIA+/RPR-/FTA- did not result in detection of any new cases of syphilis, suggesting that retesting may be unnecessary. The EIA appears more effective than the RPR alone at detecting latent syphilis. Four cases of primary syphilis would not have been identified based on EIA testing alone, suggesting that additional testing is warranted for persons in whom primary syphilis is suspected.
Implications for Programs, Policy, and/or Research: Additional data are needed to guide clinical practice for clients with discordant syphilis lab results, including recommendations for persons without syphilis who test EIA positive.