A Dual-Platform Point-of-Care Test for Neurosyphilis Diagnosis

Abstract

We optimized the DPP Chembio syphilis assay on cerebrospinal fluid for the diagnosis of neurosyphilis and found that this point-of-care test has a diagnostic performance that is similar to a clinicoserological definition of neurosyphilis. Supplemental digital content is available in the text. Background The diagnosis of neurosyphilis relies on cerebrospinal fluid (CSF) abnormalities (pleocytosis, elevated protein) and CSF–Venereal Disease Research Laboratory (VDRL) test. In resource-limited settings, the CSF-VDRL test may not be widely available. Methods We optimized a commercial immunochromatographic strip test, the DPP Chembio syphilis assay, for performance with CSF and tested centrifuged CSF samples of 71 patients with syphilis (35 with neurosyphilis and 36 without neurosyphilis). A CSF dilution of 1:4 was chosen based on agreement with CSF pools with documented results from the CSF-VDRL test and fluorescent treponemal antibody absorption test on CSF. Using an electronic reader, we obtained unit values of treponemal and nontreponemal antibodies for all study samples and generated a receiver operating characteristic curve; using the Youden index, we established diagnostic cutoffs with optimal sensitivity and specificity. Results Diagnostic sensitivity of the nontreponemal test was 80% (95% confidence interval, 63%–92%) and specificity was 97% (95% confidence interval, 85%–100%) for neurosyphilis diagnosis using a reactive CSF-VDRL that improved after neurosyphilis therapy as a criterion standard. Conclusions In this small study, the DPP Chembio test showed promising results for neurosyphilis diagnosis. Further studies are needed to assess its performance in resource-limited settings.