Rapid diagnostic testing for syphilis in Arctic communities (the STAR study): a multisite prospective field diagnostic accuracy study in an intended-use setting.

ABSTRACT

OBJECTIVES: We evaluated the field diagnostic accuracy of a syphilis rapid test (RDT), using serum and whole blood by non-laboratorians in two Canadian Arctic communities. METHODS: We implemented a multisite prospective field evaluation wherein patients were screened by an RDT containing treponemal and non-treponemal components (Chembio DPP® Syphilis Screen & Confirm) between January 2020 and December 2021. Venous whole blood and serum were collected for rapid testing and compared with laboratory-based serology reference testing using a reverse sequence algorithm of treponemal and rapid plasma reagin (RPR) testing. RESULTS: Overall, 135 whole blood and 139 serum specimens were collected from 161 participants during clinical encounters. Treponemal-RDT sensitivity against a treponemal-reference standard (38/161 confirmed cases) was similar for serum (78% [95% CI 61-90%]) and whole blood (81% [95% CI 63-93%]). In those with RPR titres ≥18 (i.e. suggestive of recent/active infection), sensitivity increased to 93% (95% CI 77-99%) for serum and 92% (95% CI 73-99%) for whole blood. Treponemal-RDT specificity was excellent (99% [95% CI 95-100%]) for both specimen types. Non-treponemal-RDT sensitivity against RPR was 94% (95% CI 80-99%) for serum and 79% (95% CI 60-92%) for whole blood. Sensitivity increased to 100% (95% CI 88-100%) for serum and 92% (95% CI 73-99%) for whole blood when RPR titres ≥18. RDT performance with whole blood was similar to that with serum. DISCUSSION: Non-laboratorians using the RDT accurately identified individuals with infectious syphilis under real-world conditions in an intended-use setting at the point of care. Implementing the RDT can eliminate treatment delays and may enhance disease control.