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Test for syphilis, yaws more sensitive in high-titer infections
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Although a rapid diagnostic test had both good sensitivity and specificity in testing for syphilis and yaws, the test’s sensitivity decreased in cases with lower antibody titers, according to a meta-analysis published in Clinical Infectious Diseases.
Researchers analyzed thousands of evaluations of the Dual Path Platform Syphilis Screen and Confirm test, which uses both treponemal and nontreponemal components for a diagnosis.
“Several recent publications have reported on the performance of this assay and have reported good test performance, although variations have been noted in both the sensitivity and the specificity of the nontreponemal component of the test in particular,” Michael Marks, MBBS, MSc, of the clinical research department at the London School of Hygiene & Tropical Medicine, and colleagues wrote. “To provide more accurate estimates of performance we conducted an individual patient-level meta-analysis on the performance of the [Dual Path Platform rapid diagnostic test (DPP-RDT)] for the diagnosis of both syphilis and yaws.”
Treponemal tests have a high specificity but can test positive even after an infection has cleared, the investigators wrote, while nontreponemal tests have a lower specificity but can more accurately identify a current infection.
Syphilis can cause stillbirths and kill newborns when transmitted from mother to child, and there are an estimated 300,000 such deaths in Africa annually, according to the researchers. In 2012 WHO called for the eradication of yaws by 2020, with the development of RDTs as a priority.
Marks and colleagues used PubMed to identify nine international studies that included data from 7,267 DPP-RDTs. They determined the test had a higher sensitivity in patients with higher-titer rapid plasma reagins (RPRs; ≥1:16) compared with those with lower-titer RPR in both the treponemal (98.2% vs. 90.1%; P < .0001) and nontreponemal (98.2% vs. 80.6%; P < .0001) components.
“The major limitation of the DPP-RDT is the reduced sensitivity of the test for low-titer disease,” the researchers wrote. “As RPR titers tend to be higher in patients with syphilis than in patients with yaws, this reduced sensitivity is likely to be a greater problem when using the test as part of yaws eradication efforts, especially as a high-sensitivity assay will be needed to ensure all cases are detected to confirm the final eradication status of the infection.” – by Andy Polhamus
Disclosure: The researchers report no relevant financial disclosures.
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