Use of Oral Fluid in a Rapid Syphilis Test Assay

BACKGROUND: From 2014 to 2015, the syphilis rate in the United States increased by 19%, reaching its highest rate since 1994. Currently, point-of-care syphilis assays use fingerstick or venipuncture whole blood to identify Treponema pallidum (TP) antibodies by qualitative immunoassay. However, patients and providers prefer oral fluid testing to whole blood testing. In this study, we aimed to determine whether a rapid syphilis test intended for use on whole blood could be used to detect TP antibodies in oral fluid. METHODS: Oral fluid was collected from 72 participants using the Super•SAL™ Oral Fluid Collection Device (Oasis Diagnostics®, Vancouver, WA). The device uses an absorbent cylindrical pad to collect and filter ~1 mlml of oral fluid. Oral fluid filtrate was tested using the SD Bioline Syphilis 3.0 rapid test (Alere Diagnostics, MA) following manufacturer directions for whole blood. TP particle agglutination (TPPA) and rapid plasma reagin (RPR) results derived from participants’ medical records were used as reference values. We used three different definitions as comparators: 1: TPPA reactive; 2: TPPA and RPR reactive and 3: TPPA reactive and RPR titer >1:4. Those with non-reactive TPPA and RPR results were considered seronegative. We calculated the sensitivity and specificity for definition 1 and sensitivity for definitions 2 and 3. We used the exact binomial method to determine 95% confidence intervals (CI). RESULTS: With definitions 1, 2, and 3, respectively, sensitivity was 83.3% (CI: 67.2, 93.6), 86.4% (CI: 65.1, 97.1), and 100% (CI: 71.5, 100). Specificity was 47.2% (CI: 36.5, 75.5). CONCLUSION: The high sensitivity of the SD Bioline Syphilis 3.0 test using oral fluid suggests a strong potential for the development of accurate rapid oral syphilis tests. Sensitivity increased with higher RPR titer. False positive results may be due to the presence of non-venereal treponemal antibodies in oral fluid. Further research and development are needed to optimize specificity. DISCLOSURES: All authors: No reported disclosures.