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Team Adopts Luminex xTAG GPP to Study Parasitic Infestation in Patients Returning from Tropics

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NEW YORK (GenomeWeb News) – A team of researchers from the University of Basel in Switzerland have opted to implement Luminex's xTAG Gastrointestinal Pathogen Panel for routine diagnostics after comparing the multiplex assay with conventional approaches.

The group, based within the university's division of infection diagnostics, made the decision to move to the GPP, which covers 15 diarrhea-causing pathogens, after using it to test stool samples from pediatric patients with gastroenteritis and adult travelers returning from the tropics. The group described the results of its evaluation in the journal Infection this month.

"We are using it now as a routine assay," said Christiane Beckmann, a microbiologist at the University of Basel and lead author on the paper. "It's not a super cheap test but if you have an immunocompromised person and you need to know if they have something dangerous, then this test provides something that direct antigen detection, microscopy, or culture cannot do."

Austin, Texas-based Luminex says its xTAG GPP can detect hospital-acquired infections, targeting a total of 15 gastrointestinal pathogens in a single bead array-based assay. The company garnered a CE-IVD mark for the test in 2012, followed by US Food and Drug Administration clearance last year for a version of the assay containing 11 pathogens for use on its LX 200 and benchtop MagPix instruments.

Beckmann said that her lab decided to try the assay after looking for a multiplex alternative to standard tests, which include PCR-based direct antigen testing, culture, and microscopy. "We are a diagnostics lab and I am mainly involved in molecular diagnostics," Beckmann said. "We already have a multiplex assay for respiratory pathogens and we wanted something similar for testing stool samples."

Though Luminex does offer an xTAG Respiratory Viral Panel, Beckmann said that her lab currently uses another platform to test for respiratory pathogens, and noted that the GPP is the first test the lab has employed that uses Luminex's bead array technology.

According to Beckmann, her lab was drawn to the GPP because of its turnaround time and ease of use.

"You can get a result for 15 pathogens within a few hours and it is easy to handle if you are working in a molecular diagnostics lab because a technician can easily perform the assay with no problems," she said.

As part of its evaluation, Beckmann's lab used the GPP to test 312 consecutive stool samples, 127 of them from pediatric patients with gastroenteritis, and the remaining 185 from adult travelers returning from the tropics with suspected parasite infestation. Of the 185 samples from adult travelers, 21 — or 11 percent — were positive, with enterotoxigenic Escherichia coli being the predominant pathogen. The second most frequently detected pathogen was the parasite Giardia lamblia, which was detected in five of the 21 positive samples.

Sixty-six, or 52 percent, of the pediatric samples were positive, with rotavirus being the most prevalent. In the paper, the authors acknowledged that rotavirus vaccination is not yet part of the standard vaccine program in Switzerland, which they said explained the high prevalence of the virus in young children. The GPP increased detection rates of the virus by 32 percent compared to direct antigen testing, and the validity of the data was confirmed by independent rotavirus-specific PCR, they wrote.

Beckmann noted that her lab obtained the samples from adult travelers through collaboration with the Swiss Tropical and Public Health Institute, also based in Basel. "Since we are collaborating, we thought this might be a good patient group to look at and to see how valuable this assay might be for patients with suspected parasitic infestation," she said.

While Beckmann was surprised by the relatively low amount of parasitic infections detected in the adult travelers' samples, she said she was pleased by the higher amount of positives in the pediatric samples, including eight co-infections. Her lab also detected seasonality to the pediatric infections, with more viral infections occurring during the winter months compared to summer months.

Given the results of the evaluation, Beckmann's lab developed a somewhat nuanced approach to implementing the GPP, favoring its use in some cases while relying on standard approaches in others. According to the paper, the "major role" of the assay should be for testing immunocompromised patients with a broad differential diagnosis when rapid results are needed, as the information obtained from the test could have an impact on clinical management, resulting in reduced hospital stay and costs.

For children with gastroenteritis, the authors recommend that direct antigen testing be done first and then followed up with the GPP should the initial results be negative or should additional pathogens be suspected. For adult travelers returning from the tropics, the authors recommend restricting the use of the GPP to patients with the clinical diagnosis of gastroenteritis.

"I think it is something that is really a great tool for diagnostics," said Beckmann of the GPP. "It's something that you would use first as a screening tool if you need a rapid answer," she said.

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