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CDC Study Validates Fast-track Diagnostics' Respiratory Assay Panel, Flexible MDx Approach

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Researchers from the US Centers for Disease Control and Prevention this month published a study validating a multiplexed real-time PCR assay panel manufactured by Luxembourgian molecular diagnostics firm Fast-track Diagnostics.

The paper is one of the first peer-reviewed publications to validate Fast-track's "syndromic" molecular diagnostics approach, which involves creating broad assay panels with the patient's symptoms and disease in mind, as opposed to assaying for a particular suspected pathogen.

The study also helps validate Fast-track's strategy of designing highly multiplexed real-time PCR assays with maximum flexibility in sample prep and instrument platform so that labs can easily implement them using their existing setups.

Fast-track is now hoping that several of its ongoing international collaborations — including a global childhood pneumonia epidemiology study funded by the Bill and Melinda Gates Foundation and an infectious disease testing laboratory network supported by French non-profit Fondation Mérieux — will yield additional published data validating its assay panels for respiratory disease, gastrointestinal disease, and meningitis, among others.

Founded in 2007, Fast-track has quickly expanded its molecular diagnostic test menu and grown its business. The company currently offers more than two dozen assay kits for a variety of infectious diseases, 23 of which are CE marked for in vitro diagnostic use in European and other countries. None of the company's kits is approved for human diagnostic purposes in the US, although Fast-track does sell its kits to US customers for research use only.

In 2011, Fast-track supplied more than 18,000 kits for more than 136,000 patient samples, representing 235 percent growth over 2010. In 2011 it sold its kits to 72 customers and distributors in 28 countries, as opposed to 35 customers and distributors in 18 countries the previous year.

The company has carved out a niche in the molecular diagnostics arena by leveraging existing, proven real-time PCR technologies and combining them in such a way as to offer maximum flexibility to potential customers.

In addition, instead of focusing on developing new technology to increase the multiplexing capability of real-time PCR, Fast-track instead works within existing limitations by designing its assays in multiple tubes, with each tube typically assaying for four targets.

"We limit ourselves to four pathogens in one tube," Tanja Sendzik, bacteria portfolio manager at Fast-track, told PCR Insider this week. "We have an open [assay] system, so we fully validate our tests on [Life Technologies' Applied Biosystems] 7500 [Fast Dx]; but you could also use a Bio-Rad CFX96, a [Qiagen] Rotor-Gene Q, or [Roche] LightCycler system."

In addition, all of Fast-track's assay kits use TaqMan real-time PCR chemistry; and, in order to keep costs lower for its customers, the company does not supply master mix or DNA extraction methods with its reagents. Instead, it has validated its kits with products from several different vendors — but particularly recommends Life Technologies' Ambion master mixes; and extraction products from Qiagen and BioMérieux.

Fast-track validates its assay kits with all other vendors' products in house before recommending them to customers.

Despite the wide variety of technologies that can complement Fast-track's kits, the assays "always follows the same workflow, so it doesn’t matter if the customer wants to detect stool parasites, or respiratory viruses, or viral meningitis bacteria — the extraction procedure is always the same, and the pipetting setup is always the same, so they can combine different tests in one plate," Sendzik said.

Fast-track views its "syndromic" approach to assay panel design as one of the most important aspects of its strategy, Sendzik said.

"The idea is not to differentiate between virus detection and bacteria detection, but to screen for all pathogens that could be responsible for a certain syndrome — so neglecting the origin of the pathogen [and] combining bacteria, virus, and fungus in one panel," she said.

"In most cases where [physicians] prescribe antibiotics … if you screen [later on] using a molecular diagnostic you will find it is not bacteria that caused [the disease], but that it was a virus," she added. "But [physicians] wouldn't necessarily look for those [in the first place]. That's one of the main points of the CDC paper, that you would be surprised what you would find, especially pathogens that you would not expect, and you suddenly find them once you multiplex."

In the paper, published as an accepted manuscript last week in the Journal of Virological Methods, Fast-track's collaborators at CDC validated the company's respiratory pathogen panel, FTD Respiratory Plus, a six-tube multiplex assay designed to detect up to 20 different viruses and several bacterial pathogens.

Specifically, the researchers compared FTD Respiratory Plus with in-house single-plex real-time PCR assays for detecting 16 common respiratory viruses. The FTD Respiratory Plus assay correctly identified 26 diverse respiratory virus strains; 35 of 41 (85 percent) external quality assessment samples spiked with cultured virus; and 232 of 263 (88 percent) archived respiratory specimens that tested positive for respiratory viruses by in-house assays.

In addition, of 308 prospectively tested respiratory specimens selected from children hospitalized with acute respiratory illness, 270 (87.7 percent) and 265 (86 percent) were positive by FTD Respiratory Plus and in-house assays for one or more viruses, respectively, with combined test results showing good concordance.

"Most [FTD Respiratory Plus] assays performed comparably with in-house assays for most viruses while offering enhanced throughput and easy integration by laboratories using conventional real-time PCR instrumentation," the authors wrote in the paper's abstract.

Fast-track's Respiratory Plus assay is one of three in the company's stable of respiratory pathogen panels: it also offers the FTD Respiratory 21, which is essentially the same assay without the bacterial targets; and the FTD Respiratory 33, which detects 20 viruses, 11 bacteria, and one fungus, and is more suited to epidemiological studies, Sendzik noted.

Other offerings from Fast-track include assay panels for gastroenteritis, viral and bacterial meningitis, fever and rash, eye infections, and sexually transmitted diseases.

Fast-track offers its kits in bulk so laboratories can test four, six, or 12 patients at a time and, as such, the company targets mostly mid- to high-volume molecular testing laboratories.

"We collaborate [in Luxembourg] with a diagnostics lab [that] runs most of our tests in their routine daily diagnostics, and sometimes they will run up to 200 samples a day," Sendzik said. "So these can be run in medium or bigger labs. It's definitely not point of care as it stands right now, because you would need experienced [technicians], and the whole workflow takes a while — you would have your results usually in three to four hours, including extraction, pipetting, et cetera."

Fast-track is betting that this flexible approach will continue to be attractive to customers seeking reliable molecular diagnostic testing at a relatively low cost, thanks to the multiplexed nature of the tests and the use of existing laboratory equipment. As it stands, this cost savings is particularly attractive in resource-poor areas of the world.

To wit, Fast-track is part of two key international partnerships that may serve to further validate its kits in these settings. The first is a study initiated last August called PERCH (pneumonia etiology research for child health). Funded by the Gates Foundation, the effort is a collaboration between five African and two Asian research sites coordinated by the International Vaccine Access Center at Johns Hopkins Bloomberg School of Public Health.

"This is a three-year study … to track the spread of different viruses and bacteria in these different climate zones in the world, and determine which pathogens [and] co-infections give the worst outcome in infected children," Sendzik said. "Unfortunately there is no data out yet, because they just started enrollment last year."

The second major collaboration is the GABRIEL (global approach for biological research on infectious epidemics in low-income countries) Laboratory Network, organized and funded by Fondation Mérieux, a French non-profit dedicated to fighting infectious disease in underserved populations.

Based around the foundation's two applied research units in Lyon and Beijing, GABRIEL brings together Rodolphe Mérieux Laboratories, local reference laboratories, academic or private sector research institutions, hospitals, universities, and diagnostic firms including Fast-track, with the goal of conducting infectious disease epidemiological studies and disseminating new diagnostic tools and know-how in resource-poor areas of the world.

Fast-track is hoping that these collaborations, among others, will soon produce additional data for peer review and publication that will serve to further validate its molecular diagnostic kits.

"We always do the final validation of our kits [in house] on real samples," Sendzik said. "And we always have ongoing small collaborations, and we try to publish this data. But sometimes it's very limited information on 20 or 40 samples, so the data might be published at conferences," for instance, instead of in peer-reviewed journals.

As for its North American plans, Fast-track will continue to market its kits as RUOs to customers in the US and Canada, and it may eventually seek regulatory approval in the states for select kits — though this is not an immediate concern, according to Sendzik.

"We have been looking into it," she said. "It would be a matter of the company deciding which tests it would try to get approved."

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