(P408-LB) Four polyvalent screening assays in comparison to the treponema pallidum particle agglutination assay

Background: Annually, 6-7 million novel infections with treponema pallidum spp. pallidum occur worldwide with an upward trend. Especially in the early phase of syphilis patients are highly infectious and need to be identified to avoid clinical sequalae and further transmission. Without treatment those bacteria can cause severe symptoms such as neurosyphilis.

In 2021, Fujirebio company announced to stop the production of the treponema pallidum particle agglutination assay (TPPA), which is a backbone for syphilis diagnostics in Europe. To develop an alternative diagnostic strategy, we examined polyvalent screening tests (in terms of their sensitivity, specificity and correlation to TPPA).

Methods: Specimen were analyzed using TPPA as gold standard and four screening tests each: CMIA (Abbott), CLIA (DiaSorin), ECLIA (Roche), EIA (Euroimmun). The panel consisted of well characterized negative, borderline and positive samples. We calculated sensitivity and specificity for each of these tests. Additionally, we evaluated a reduction of the cutoff values of each test in deviation from the manufacturer's specifications to achieve the sensitivity of the TPPA test.

Results: 1,813 specimens were included. Sensitivity, specificity and correlation with the TPPA were not comparable to the TPPA in terms of test performance for none of the included tests (table 1).

Conclusion: Those results lead to the conclusion that reducing the cutoff values for the CMIA, ECLIA and CLIA would be useful in order to increase the proportion of true positive results. The results showed that a reduction of cut offs would be feasible in terms of diagnostic accuracy to a low proportion of additional, false-positive test results, increasing the sensitivity especially for early phases of infection distinctly without much influence on the specificity.