The point-of-care (POC) Dual Path Platform (DPP®) assay (Chembio, Medford, NY) may be an inexpensive tool for the diagnosis of neurosyphilis, according to research results presented at the virtual Conference on Retroviruses and Opportunistic Infections, held from March 8 to 11, 2020.

The global burden of neurosyphilis remains high and the disease can cause severe disability. Furthermore, the ability to diagnose this illness in resource limited settings is challenging. Investigators, therefore, conducted a study to evaluate whether the DPPassay, originally developed to detect serum treponemal and nontreponemal antibodies, could be used on cerebrospinal fluid (CSF) to diagnose neurosyphilis.

The CSF from lumbar punctures were retrospectively analyzed via a 1:1 case control study from 72 patients with syphilis. Confirmed cases were defined by reactive CSF-Venereal Disease Research Laboratory (VDRL) test with or without CSF pleocytosis that normalized after neurosyphilis therapy. Controls without neurosyphilis had a nonreactive CSF-VDRL and a CSF white blood cell (WBC) ≤5/μL. Case controls were matched by age, HIV status and syphilis stage.

There were equal percentages of men, patients with HIV and similar age between cases and controls. Higher serum rapid plasma regain (RPR), CSF WBC and CSF VDRL titers were found in cases compared with controls. The CSF treponemal antibody POC test result was > 89 units in 31 of 36 cases and 5 of 36 controls. The CSF nontreponemal antibody POC test result was >7.7 units in 29 of 36 cases and 1 of 36 controls. This resulted in a sensitivity and specificity of 86% (for both) for the treponemal test compared with 81% and 97%, respectively, for the nontreponemal test.


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According to researchers, a combination of high sensitivity treponemal and high specificity nontreponemal results may enable neurosyphilis diagnoses with a high degree of certainty. The DPP,therefore, may have widespread application for use in resource limited settings because it does not require highly trained personnel or additional laboratory facilities. Further studies should be conducted to examine its performance in resource limited settings.

Reference

Gonzalez H, Koralnik I, Tantalo L, Huhn GD, Orban Z, Marra C. A point-of-care assay for diagnosis of neurosyphilis. Paper presented at: Conference on Retroviruses and Opportunistic Infections; March 8–11, 2020; http://www.croiconference.org/sites/default/files/uploads/croi2020-boston-abstract-ebook.pdf. Accessed March 19, 2020.