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Novel syphilis test distinguishes active vs. past infections
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A commercially available, point-of-care syphilis screening test differentiated between active syphilis infection and past infection, and thus may eliminate unnecessary therapy, according to recent findings.
“In addition to unnecessary treatment, the diagnosis of an infection that is primarily sexually transmitted may lead to psychosocial trauma, including stigma and partner violence,” researchers from Australia wrote in Clinical Infectious Diseases. “In many settings, it is already challenging enough for women to deal with the consequences of such a true diagnosis, and false-positive test results can compound this burden further. There is therefore an urgent need for a syphilis POC [point-of-care] test that can make the distinction between active and past treated infection.”
In a cross-sectional study, researchers used 1,005 stored serum specimens to evaluate the performance of the dual path platform (DPP) Syphilis Screen and Confirm Assay (Chembio Diagnostic Systems) with the results of conventional laboratory-reference treponemal and nontreponemal tests. The DPP assay is designed as a POC test and uses an immunochromatographic strip platform to simultaneously detect treponemal and nontreponemal antibodies using serum, plasma or whole blood without requiring refrigeration. The corresponding treponemal and nontreponemal reference tests included immunoassays and rapid plasma reagin.
The serum samples were chosen from Australia’s Victorian Infectious Diseases Reference Laboratory in Melbourne and the South Eastern Area Laboratory Service in Sydney. Very high rates of syphilis among gay men recently were reported in both cities, particularly among HIV-infected men.
The researchers evaluated the DPP test outcome agreement with the conventional test results based on serological and clinical classifications.
The treponemal line sensitivity of the DPP test was 89.8% (95% CI, 87.3%-91.9%) and its specificity was 99.3% (95% CI, 97%-99.9%). The nontreponemal line sensitivity of the DPP test was 94.2% (95% CI, 91.8%-96%), and its specificity was 62.2% (95% CI, 57.5%-66.6%) Concordance was observed between the DPP test outcome and both reference tests results for 94.3% of the 404 high-titer infections, 90.1% of 121 low-titer infections, 27.5% of 211 past or treated infections, and 78.1% of 242 cases determined not to be syphilis. Of the past or treated infections, incorrect identification as active infection occurred in 49.8%, with an additional 22.8% classified as not syphilis.
The researchers said the benefits of the DPP test should be weighed based on the characteristics of an individual population.
“DPP test use would result in identification of over 93% of active syphilis infections, while just over half of past infections would be diagnosed as past or not syphilis, avoiding unnecessary treatment compared to other POC tests,” the researchers wrote. “This may be at the expense of missing some active infections, thus its potential benefits will depend on the prevalence of past vs. active infection in a population.”
Disclosure: The researchers report no relevant financial disclosures.
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