Abstract

INTRODUCTION: Most syphilis point-of-care (POC) tests detect treponemal antibodies, which persist after successful treatment. Subsequent POC tests are positive, despite no active infection, and can lead to unnecessary treatment. We evaluated a new POC test, incorporating a non-treponemal component, to distinguish active from past infection. METHODS: Sera stored at two Australian laboratories were tested with DPP Screen-and-Confirm Assay. Treponemal and non-treponemal test lines were compared to corresponding conventional treponemal and non-treponemal reference test results: immunoassays and rapid plasma reagin(RPR), respectively, with RPR quantification by endpoint titration. POC test outcome concordance with conventional test results was assessed according to serological and clinical categories. RESULTS: Among 1005 sera tested, DPP treponemal line sensitivity was 89.8%(95%CI 87.3-91.9%) and specificity was 99.3%(97.0-99.9%). DPP non-treponemal line sensitivity was 94.2%(91.8-96.0%) and specificity was 62.2%(57.5-66.6%). DPP test outcome (pair of test lines) was concordant with both reference test results for 94.3% of 404 high-titre infections; 90.1% of 121 low-titre infections; 27.5% of 211 past/treated infections, and 78.1% of 242 classified as not syphilis. Among 211 past/treated infections, 49.8% were incorrectly identified as active infection and a further 22.8% as not syphilis. CONCLUSION: DPP test use would result in identification of over 93% of active syphilis infections, while just over half of past infections would be diagnosed as past or not syphilis, avoiding unnecessary treatment compared to other POC tests. This may be at the expense of missing some active infections, thus its potential benefits will depend on the prevalence of past versus active infection in a population.