This story was originally posted on July 17.
Luminex's xTAG Gastrointestinal Pathogen Panel could be of use not only to clinical laboratories, but public health laboratories monitoring disease outbreaks, according to a new study.
A team of investigators at the City of Milwaukee Public Health Laboratory recently evaluated the GPP's ability to screen for diarrhea-causing pathogens, including bacteria and viruses, in fecal specimens. The overall comparative performance of the GPP with conventional methods in clinical samples was 94.5 percent, with 99 percent sensitivity. The assay's ability to multiplex and five-hour turnaround time prompted the lab to adopt it for routine use in public health monitoring.
Scientists from the lab detailed their assessment of the GPP in a Journal of Clinical Microbiology, paper published online last week.
"The impetus [for this study] came from public health outbreaks where we had to look at a lot of things simultaneously, to find out what is the root cause of the outbreak," said corresponding author Sanjib Bhattacharyya, who is deputy director of the lab.
"Prior to the GPP, the standard practice to a chronic gastrointestinal pathogen situation was that the physician would request culture," Bhattacharyya told BioArray News. "This is a new ballgame," he said of the GPP. "This will allow us to look at a patient's pathogen load. It's a broad-spectrum approach for pathogen identification."
The US Food and Drug Administration cleared Luminex's bead array-based GPP assay for clinical use on its Luminex 200 instrument in January, and again for use on its benchtop MagPix system in April. The Austin, Texas-based company claims that xTAG GPP can detect hospital-acquired infections, and 15 total gastrointestinal pathogens in a single assay (BAN 4/16/2013).
Since Luminex attained clearance for the assay, two other studies have assessed the GPP's performance. The first, authored by a team at University Hospital Witten/Herdecke in Cologne, Germany, was published online in SpringerPlus in March. The second, authored by a team at Toulouse University Hospital in France, appeared in Clinical Microbiology and Infection in April.
According to Bhattacharyya, what distinguishes the new JCM study is not only that it is the first evaluation of the GPP published by a US lab, but that the Cologne and Toulouse teams were both from clinical labs, whereas the City of Milwaukee Public Health Laboratory functions both as a public health reference lab and a CLIA-certified clinical lab.
"Ours is the first to talk about the public health application of the GPP," said Bhattacharyya. "This expands the potential for this test, as there is a huge number of [public health reference] labs that are screening for pathogens," he said.
Causes for Hesitation
Bhattacharyya has been an early supporter of the GPP. When Luminex announced that the FDA had cleared the assay in January, he was quoted in a statement as saying that "routine use of xTAG GPP will allow cost-effective, timely detection of multiple pathogens, optimize use of laboratory resources, and elevate our understanding of pathogen-associated diseases in gastroenteritis."
While his lab sees the benefits of using the assay, he acknowledged that some other labs might be less enthusiastic. He noted that the FDA clearance of the assay stipulated that its findings must be considered presumptive and confirmed with a second clinical assay, in most cases PCR.
"There will be some hesitation for GPP, since FDA said you had to consider ID presumptive and then confirm," said Bhattacharyya. "That's a challenge as most labs are looking for a single test," he said.
Another factor is cost. While Bhattacharyya declined to discuss the price of the GPP, he said it was higher than conventional methods. "At the same time, there is potential here, because the information you get out of a single run is tremendous," he said. "And if you break down target-specific costs, then the prices are very comparable," he said, meaning that the cost of testing each pathogen using individual assays worked out to be about the same as the cost of the GPP.
Another issue that may slow adoption of the test is education. Bhattacharyya said that while his lab has implemented it as a first-line screen for public health outbreaks, and validated it for clinical use, it has not yet seen a request from clinicians for the test, mainly because they are not familiar with it.
"We hope our paper will add to education and understanding of next-generation testing and that it will encourage people to adopt this test," said Bhattacharyya.
On the positive side, he noted that some clinical and public health labs have already implemented Luminex's FDA-cleared Respiratory Virus Panel, and that they could be encouraged to add the GPP, given the similarities of the two assays' workflows.
"Labs doing RVP can easily adopt GPP," said Bhattacharyya. "If they already have the Luminex systems installed, there is no upfront set up cost."