Dual Treponemal and Non-Treponemal Rapid Test for Syphilis in People Living with HIV: A Diagnostic Accuracy Study

Rapid dual treponemal/non-treponemal (lipoidal antigen) tests could improve syphilis detection strategies among people living with human immunodeficiency virus (PLHIV). The World Health Organization (WHO) recommends minimum performance targets for syphilis point-of-care tests: sensitivity >80% for the treponemal component, >95% for the non-treponemal component, and specificity >90% for both. We evaluated the diagnostic accuracy of a dual treponemal/non-treponemal test in PLHIV.

Cross-sectional study using stored serum samples donated by PLHIV who had been previously enrolled in a study conducted in Cali, Colombia. The index test was the Dual Path Platform® Syphilis Screen & Confirm Assay (DPP-SSCA, Chembio Diagnostic Systems, Inc.). A combination of Treponema pallidum hemagglutination assay and treponemal enzyme-linked immunosorbent assay (ELISA) served as the reference standard for the treponemal component, and the rapid plasma reagin (RPR) test for the non-treponemal component. We estimated the sensitivity and specificity of both components.

We performed 280 DPP-SSCA on serum from 220 PLHIV (60 samples tested in duplicate). Median age: 35.2 years; 75.9% male; 53.0% with undetectable viral load; and 35.9% with previously treated syphilis. The treponemal component had 74.5% sensitivity (95% confidence interval [CI], 58.4-85.9) and 97.2% specificity (95% CI, 92.8-98.9). The non-treponemal component had 90.4% sensitivity (95% CI, 74.9-96.7) and 46.5% specificity (95% CI, 38.0-55.3).

In PLHIV, the serum-based DPP-SSCA did not meet WHO performance targets. Given the low specificity of the non-treponemal component, the development of improved diagnostic tools and rigorous validation are needed to ensure reliable and rapid diagnosis of active syphilis infection in this population.