New tests stop flu in its tracks

Nov. 1, 2010


ast year’s flu season was an anomaly, dominated by influenza A/H1N1 virus. Fewer-than-normal reported cases of seasonal flu can most likely be attributed to the number of vaccinations administered for the H1N1 virus, says David Persing, MD, PhD, chief medical and technology officer at Cepheid. “H1N1 2009 provided a cross-immunity effect.” As for the 2010-2011 flu season, Persing says a few cases of H1N1 have been reported but doubts there will be an epidemic like last year. “That could be because of vaccinations or ‘herd immunity,’ or the virus may be changing.” Three strains are expected to be circulating this year: influenzas A California/H1N1, A Perth/H3N2, and B Brisbane.

Steve Kleiboeker, PhD, DVM, chief scientific officer at Viracor-IBT Laboratories, foresees a less severe flu season. “The current vaccine has H1N1 and seasonal flus A and B. Widespread use of vaccines last year and widespread exposure may mean many people have H1N1 immunity, which would slow the spread and diminish its threat this year. Flu A viruses are known for significant mutation rates; it is possible, but not likely, that H1N1 could change sufficiently to make it a threat yet again in the 2010-2011 flu season.”

Pandemic 2009-2010 was a wake-up call for clinicians, diagnostic-test developers, and laboratorians. “One of the most important things labs learned is that they are poorly equipped to handle a surge in flu tests,” says Jeremy Bridge-Cook, PhD, senior vice president of the Assay Group at Luminex Corp. He says labs found they need to run subtype tests to identify a novel flu strain such as H1N1.

Wade Stevenson, diagnostics marketing manager for Idaho Technology, acknowledges the difficulty in being certain which strain of flu will dominate any season. “When you are talking about respiratory viruses, staying ahead is a huge challenge,” he says. “We are light years away from predicting how Mother Nature will evolve these viruses. Last year was a pretty good reminder as to how quickly influenza can mutate.”

Kleiboeker points to lessons learned: “Flu A is unpredictable in terms of genetic makeup, geographic area of emergence, levels of transmissibility, and levels of virulence. Second, excellent diagnostic capabilities are essential to understand the extent, dynamics, and impact of a highly transmissible pathogen such as flu A. Early in this pandemic, diagnostic capabilities were overwhelmed; through concerted public-health and private-sector efforts, capacity was built rapidly. Third, molecular diagnostics are far superior to any other technology for the diagnosis of flu A. Fourth, even in the face of the most pressing need, flu vaccines require many months to develop and deploy.”

“H1N1 accelerated an overall trend to move to molecular diagnostics because most could detect that novel flu strain,” says Stevenson. Persing says the rate of false positives for rapid flu tests was about 5%, driving labs to seek emergency use authorization to use molecular tests — some not yet approved by the U.S. Food and Drug Administration (FDA). “There are now FDA-cleared options for H1N1 detection — a separate assay run separate from seasonal flu — but none suited for fast turnaround testing.”

Judy Yu, senior manager of Scientific Affairs at Abbott Molecular, agrees improvements have been made. “The poor sensitivity of rapid antigen tests last year for 2009 H1N1 was primarily due to antigenic drift that caused antibodies used in older assays not to recognize the new virus very well. New antibodies against the new virus have been produced; newer rapid antigen assays can detect 2009 H1N1 with improved sensitivity. The problem can repeat if a new influenza A strain comes along, which is why molecular assays are more reliable, and much more quickly and easily updated to detect the new strains, if necessary.”
She notes, “New molecular assays with subtyping capabilities, including some with FDA clearance, are available, with satisfactory sensitivity for all subtypes. Some rapid EIA and fluorescent antibody assays were updated to detect, not necessarily distinguish, 2009 H1N1 — all with improved sensitivity for the newest strains. More improvements could be made by offering antiviral-resistance information at the same time of flu detection and subtyping.”

Yet, rapid flu tests still have a place. “What keeps them alive is that they are quick,” says Persing. “Their use has been justified in EDs, doctors’ offices, and long-term healthcare facilities, but what is really needed is speed and accuracy.” Rapid flu tests are not batched, thus, they yield results in about 45 minutes. Molecular tests usually are — a convenience for labs but not so much for physicians or patients. “If PCR takes a half hour, batching has turned it into one to three days.”

During the 2009-2010 H1N1 outbreak, Bridge-Cook says physicians relied more on reference lab-based tests than on rapid tests. “Even if results are faster, the answer needs to be reliable.” Another drawback, says Persing, is the time it takes to develop or modify rapid tests to accommodate a new strain. “You cannot force Mother Nature to make antibodies faster; so, it may take a year to make sure those antibodies work.”

While molecular flu tests are proving to be more sensitive and accurate than rapid antigen tests, they pose challenges (e.g., more expensive and require more technical expertise to run). Persing says, “Molecular tests are more adaptable. You can create PCR assays that react to specific strains by targeting specific nucleotide sequences.”

Kleiboeker explains: “Molecular tests are based on the flu strains’ genetic make-ups; as those change through genetic shift or drift, assays must change to ensure accurate detection. Sequence data indicating changes in the assay’s target regions means timely assay modification and revalidation. If flu strains do not change in their genetic make-ups, no modifications are required.”

Designers and developers of molecular tests are making them easier and faster to run, while expanding their scope. “Multiplex respiratory testing, based on molecular techniques, is more widely available this year,” says Kleiboeker. “Our assays have been reformulated to detect all circulating strains in a single test.” Stevenson’s company is working on an automated multiplex system — three instruments combined — with hands-on time of one minute, and hoping for FDA approval by next May or June. Bridge-Cook’s company is revamping its basic molecular chemistry to make its assay “easier to use and faster to perform.” This modified test should yield results in four hours and is now under FDA review. Persing’s company is developing a rapid flu test using PCR technology, with hopes to get FDA approval this flu season. With its automated cartridge system, the new test takes an hour to run. “It is essentially a single-use, disposable lab”

Kleiboeker views the long-term benefits of all these developments. “Providing accurate molecular flu tests represents a constant and formidable diagnostic challenge, which drives innovation, encouraging development of testing and vaccine production capacity while demanding productive interactions among government, public, and private institutions. This, in turn, prepares this field of science to effectively control unseen and unexpected infectious-disease public-health crises.”

Richard R. Rogoski is a freelance journalist based in Durham, NC. Contact him at [email protected].