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With syphilis rates rising sharply, syphilis tests a focus

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Amy Carpenter Aquino

November 2017—Syphilis is making a comeback. Nearly 28,000 cases of primary and secondary syphilis, the most infectious stages of the disease, were reported in the U.S. in 2016—a 17.6 percent jump over 2015 and the highest reported rate since 1993. Cumbersome, subjective nontreponemal assays and the lack of a gold standard screening method lend complexity to the diagnostic process. But new nontreponemal assay options, including the first FDA-cleared fully automated treponemal/nontreponemal dual assay, may help stem the rising tide.

Dr. Fakile

Dr. Fakile

“The best chances we have of catching people are usually in the primary and secondary phases when patients present with skin or mucosal lesions,” says Yetunde F. Fakile, PhD, a microbiologist in the Centers for Disease Control and Prevention’s Division of STD Prevention. If not identified and treated in the primary or secondary stage, syphilis enters a latent stage where there are no signs or symptoms, and the infection can go undetected for years, even decades, leading to other complications.

“The biggest issue we have is that there is no gold standard serologic test to diagnose syphilis,” Dr. Fakile says. “There’s no perfect test.”

Laboratories in the U.S. perform one of two algorithms: a traditional algorithm, which is a nontreponemal assay (rapid plasma reagin or venereal disease research laboratory), followed by a treponemal assay (fluorescent treponemal antibody absorption test, T. pallidum particle agglutination, microhemagglutination assay, or enzyme immunoassay). The reverse algorithm flips the order and begins with a treponemal assay followed by a nontreponemal assay. Both assay types have pros and cons, and neither one can be used independently of the other.

“From a laboratory medicine perspective, one of the biggest challenges is that there is not a readily available, effective direct-detection method for Treponema pallidum,” says John Schmitz, PhD, of the Department of Pathology and Laboratory Medicine, University of North Carolina School of Medicine, and director of the histocompatibility and clinical flow cytometry laboratories and associate director of the clinical microbiology/immunology laboratories, UNC Hospitals. “We can’t culture it in the lab. There aren’t antigen detection tests readily available, other than dark-field microscopy and molecular diagnostics, which aren’t widely available. That presents a challenge when one is using an antibody response to diagnose an infection.”

Of the two syphilis testing algorithms, Dr. Fakile says, “currently CDC does not recommend one algorithm over the other.”

In April the CDC issued a multifaceted call to action on syphilis, one part of which urges researchers to “develop and bring to market novel syphilis tests to rapidly diagnose active infection.” The CDC noted the sharp increase in cases of congenital syphilis, which rose 46 percent between 2012 and 2015, despite guidelines for screening of all pregnant women at the first prenatal visit. In its call to action, the CDC says: “The most commonly used tests require at least two sequential antibody tests in blood and do not confirm active syphilis infection. These blood tests are cumbersome, hard to interpret, unable to diagnose early infections, and may lead to treatment delays.”

In development long before the call to action but released shortly after, the BioPlex 2200 Syphilis Total & RPR assay received Food and Drug Administration clearance in June. “It’s a novel and improved tool for detecting and managing syphilis,” says Chisanga Lwatula, PhD, global infectious disease product manager at Bio-Rad Laboratories.

It’s a dual assay, so treponemal and nontreponemal antibodies can be detected simultaneously. “It doesn’t matter what your algorithm is,” Dr. Lwatula says. “We’ve fully automated both assays and put them into a single test. You can choose in the software to report one or the other, or both at the same time.”

It removes the complexity that comes from interpreting the nontreponemal assay result and the extra step of reflexing to a second assay, because both assays are run simultaneously.

Dr. Lwatula

Dr. Lwatula

“The goal is to improve the workflow of the laboratory,” Dr. Lwatula says. “You’re also improving patient management because you’re getting those two results a lot faster.”

The automated RPR test protects against inaccurate readings of the nontreponemal card, Dr. Lwatula says. “The RPR is subjective; you have to interpret it by eye. Some of those card-based results are very difficult to interpret, especially the ones that are low-positive. One person might call it positive, and one person might call it negative. By automating the RPR test on the BioPlex 2200 system, you have objective results interpretation.”

The BioPlex 2200 Syphilis Total & RPR assay also provides full result traceability. With the process now automated, “your results are automatic, objective, and they’re directly sent to your laboratory information system.”

The CDC did not have data on the BioPlex 2200 Total & RPR assay when Dr. Fakile spoke with CAP TODAY in October. “As a laboratorian, I can tell you that we are interested in the performance of this assay,” she says.

At the University of Chicago Medicine, Vera Tesic, MD, and her colleagues are evaluating the BioPlex 2200 Syphilis Total & RPR assay for syphilis screening.

“The most exciting news for the laboratory professional is the availability of automated platforms for detection of both treponemal as well as nontreponemal antibodies,” says Dr. Tesic, assistant professor and assistant medical director of clinical microbiology and immunology labs, Department of Pathology.

The University of Chicago laboratories used to run the traditional algorithm, screening with the nontreponemal rapid plasma reagin followed by confirmation with fluorescent treponemal antibody absorption.

“We wanted to switch from the traditional algorithm to the reverse to reduce the manual labor for doing 30 to 40 RPRs every day,” Dr. Tesic says.

Dr. Vera Tesic (right) and immunology laboratory chief technologist Ana Precy Fajardo Abeleda at the University of Chicago, where they have reduced turnaround time for the syphilis diagnostic algorithm since implementing syphilis IgG testing on the BioPlex 2200 platform. They are now evaluating the BioPlex 2200 Syphilis Total & RPR assay.

Dr. Vera Tesic (right) and immunology laboratory chief technologist Ana Precy Fajardo Abeleda at the University of Chicago, where they have reduced turnaround time for the syphilis diagnostic algorithm since implementing syphilis IgG testing on the BioPlex 2200 platform. They are now evaluating the BioPlex 2200 Syphilis Total & RPR assay.

Dr. Tesic and her colleagues implemented the reverse algorithm on the random-access BioPlex 2200 platform in early 2016. “We did syphilis IgG on BioPlex screening and then confirmed it with the RPR. The only time we would do the TP-PA [T. pallidum particle agglutination] would be when there was a positive syphilis IgG and the RPR was negative; then confirmation was needed to see if the IgG was false-positive or it was somebody who had syphilis in the past and was successfully treated. Hence the RPR in that case would be negative.”

She reports favorable results with the BioPlex 2200 platform and has high hopes for the newest assay, which she and colleagues are in the process of verifying.

“Since implementation of syphilis IgG testing on the BioPlex 2200 in our laboratory we significantly reduced turnaround time for the syphilis diagnostic algorithm, and we expect further reduction using the Syphilis Total and RPR assay,” Dr. Tesic says. The assay provides RPR titer up to 1:64.

The fully automated RPR capability of the BioPlex assay makes it only the second FDA-cleared assay with nontreponemal RPR automation available in the United States. Dr. Schmitz of UNC has been studying the AIX1000 fully automated RPR syphilis testing system, from Gold Standard Diagnostics, which the FDA cleared in November 2015.

“We looked at over 1,000 samples submitted to the laboratory and compared the automated system with our manual RPR method,” Dr. Schmitz says. He declined to comment on the performance of the AIX1000 assay pending publication of the UNC study.

He describes the AIX1000 automated system, which runs on the AIX1000 RPR automated processor, as “a pipetting device outfitted with optics, basically a digital camera.” It has software, he says, that can interpret the patterns in the wells of the microplates that is used in this system to look for positive reactions in the RPR test system.

Another company, Arlington Scientific, hopes to have FDA clearance soon for its fully automated nontreponemal assay, which runs on the ASI Evolution syphilis analyzer. Mike LaDow, marketing director, cites a 2015 CDC study that found that the ASI RPR assay detected syphilis infection 14 days earlier than several treponemal assays.

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