Field evaluation of the performance and testing costs of a rapid point-of-care test for syphilis in a red-light district of Manaus, Brazil

Abstract

Objectives: To assess the performance, usefulness and cost of a rapid treponemal antibody assay (VisiTect Syphilis) to detect syphilis in high-risk populations.

Methods: STI clinic attenders in Manaus (Brazil) were screened for syphilis using the fluorescent treponemal antibody absorption (FTA-ABS) test and a non-treponemal test (Venereal Diseases Research Laboratory [VDRL]), and for HIV. Fingerprick blood samples were tested with VisiTect Syphilis. The rapid test was evaluated against the reference FTA-ABS, and for its usefulness in detecting active syphilis (FTA-Abs and VDRL positive). Operational performance was assessed through providers' and patients' interviews. An economic evaluation was conducted from the provider's perspective.

Results: 510 patients (60% men) were enrolled, of whom 13 (2.5%) were HIV-1 seropositive. Syphilis prevalence (FTA-Abs) was 18%, and active syphilis prevalence was 7.5%. 11% (57/506) of samples were positive by VisiTect. The sensitivity, specificity, positive and negative predictive values of VisiTect Syphilis were 57% (95%CI 45.8-66.7), 99% (95%CI: 97.0-99.6), 91% (95%CI 80.0-96.7) and 91% (95%CI 88.0-93.5), respectively. VisiTect Syphilis identified 79% (30/38) of active syphilis cases. The cost per-case-of-syphilis was $16.8 for VDRL, $33.2 for low-cost and $56.3 for high-cost VisiTect Syphilis; the cost per-case-of-active-syphilis was $21.3, $57.5 and $97.6, respectively. Patients identified fingerprick pain and preference for venous blood collection as minor barriers to test use.

Conclusion: VisiTect Syphilis had low sensitivity in field use and was less cost-effective than conventional VDRL. However, rapid and correct identification of a high proportion of active syphilis cases combined with operational characteristics suggest a role in high-risk populations.