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Background: Reverse sequence screening for syphilis, in which an automatable, treponemal enzyme immunoassay (EIA) is performed first and followed by a non-treponemal test for reactive specimens, has been used increasingly in the US. The EIA is objective, efficient and believed to be more sensitive than the RPR because treponemal antibodies appear before non-treponemal antibodies; however discrepant results (EIA-/RPR+/FTA+) have been detected. Howard Brown staff routinely request additional serology for all symptomatic patients to ensure appropriate diagnosis and clinical management.
Objectives: To describe discordant syphilis test results among patients presenting with symptoms of primary syphilis infection at a high-morbidity STD clinic.
Methods: STD clinic charts from January 2009-December 2011 were reviewed and 52 patients met the following inclusion criteria: suspected primary syphilis lesion, at least one positive syphilis test at visit, and no history of syphilis.
Results: Of these 52 patients, 26 had a positive EIA test: 23 were EIA+/RPR+ and 3 were EIA+/RPR-/FTA+. 26 had EIA results that were equivocal (2) or negative (24). Both equivocal cases were RPR+/FTA+. Of the 24 EIA- suspect cases, 15 were RPR+/FTA+ and 9 were RPR-/FTA+. No symptomatic patients were EIA+/RPR-/FTA-. Follow-up testing information was available for 11/24 initially EIA- patients. Two were re-exposed and 2 were symptomatic at follow-up making interpretation difficult; all 4 of these were EIA+. Of the remaining 7, 5 turned EIA+ and 2 remained EIA-.
Conclusions: The EIA was less likely to be positive than the RPR, calling into question the effectiveness of reverse sequence diagnostics in persons with primary symptoms.
Implications for Programs, Policy, and Research: Use of the EIA as a screening test may result in underdetection of primary syphilis, particularly if symptoms are occult. Additional serologic testing may be warranted for patients with primary syphilis symptoms. Further evaluation of the performance of the EIA for detecting primary syphilis is warranted.