The Significance of Isolated Reactive Treponemal Enzyme Immunoassay in the Diagnosis of Early Syphilis

Background: The Treponemal test algorithm for syphilis screening is widely used. A diagnostic challenge between identifying early syphilis versus a false positive signal occurs in cases where the treponemal enzyme immunoassay (EIA) is reactive and confirmatory T pallidum particle agglutination assay is negative. We investigated the diagnostic outcome of isolated reactive EIA in patients attending a sexual health clinic. Methods: Results of syphilis serology tests carried out at Birmingham Whittall Street Clinic between August 10, 2010, and November 31, 2014, were reviewed. Cases with isolated EIA were routinely invited for repeat syphilis serology. Outcomes of patients with isolated EIA were reviewed and the proportion with confirmed positive syphilis serology on their repeat test identified. The number of isolated EIA cases needed to retest to identify 1 case of early syphilis was calculated. Results: A total of 121,724 syphilis screening tests were performed. Among the 1561 individual patients with reactive EIA sera, 316 (20% of total reactive tests) had isolated reactive EIA. Repeat syphilis serology results of 163 patients were reviewed; 106 patients remained with isolated reactive ETA, 50 had negative EIA test and 7 (4.3%) had confirmed reactive ETA. Of the 7 patients, 2 had evidence of early syphilis infection. The number of isolated ETA needed to retest to identify 1 case of early syphilis was 81.5 (95% confidence interval, 22.9-671.4). Conclusions: Routine recall of patients with isolated ETA sera is not warranted. Risk of acquisition or presence of early syphilis should be assessed independently and irrespective of a negative syphilis screening test or isolated ETA.