Background:
Testing for syphilis relies on the collection of venous blood specimens for serological analysis. However, there is a need to identify new diagnostic tests that do not require phlebotomists for specimen collection. In 2003, the FDA-clearance of OraSure for HIV antibody testing revealed the potential of utilizing oral fluid in diagnostic testing. We investigated the use of oral fluid specimens for syphilis testing.


Objective:
We sought to determine the feasability of using oral fluid as a specimen for syphilis (TPPA) testing.

Method:
We compared Treponema pallidum Particle Agglutination (TPPA) test results from contemporaneously collected oral fluid with venous specimens from the same patient. We used the OraSure HIV-1 oral fluid collection device and tested oral fluid for the presence of syphilis antibodies using the Serodia TPPA kit (Fujirebio, Japan). TPPA-reactive serum specimens were also analyzed by the Venereal Disease Research Laboratory (VDRL) test (Becton, Dickinson and Company, USA) to measure VDRL titer.

Result:
Among 250 patients, 168 (67%) had syphilis infection. There were 20 (12%) paired specimens positive by both specimen types; 148 (88%) specimens were found TPPA-positive in serum while TPPA-negative in oral fluid TPPA; 79 specimens were TPPA-negative in both oral fluid and serum; 3 specimens were TPPA-positive in oral fluid and negative in serum. The sensitivity and specificity of TPPA using oral fluid was 12% and 96% respectively. TPPA performance did not correlate with VDRL titer.


Conclusion:
Oral fluid can also be used as an analyte in TPPA analysis with little impact in assay specificity. The use of oral fluid as a specimen in TPPA results in an approximate 8-fold loss in assay sensitivity when compared to serum TPPA. Further research is needed to improve the sensitivity of the TPPA in oral fluid specimens for clinical use.


Implications:
This work investigates a new TPPA methodology that may facilitate broader screening for syphilis.