New Influenza Tests Faster, More Accurate, Study Suggests

Marcia Frellick

September 08, 2017

New tests are faster and more accurate in diagnosing influenza A and B in both children and adults than traditional rapid influenza diagnostic tests (RIDTs), a meta-analysis published online September 5 in Annals of Internal Medicine suggests.

Joanna Merckx, MD, from McGill University Health Centre in Montreal, Quebec, Canada, and colleagues, reviewed 162 studies (130 of RIDTs, 19 of

digital immunoassays [DIAs], and 13 of rapid nucleic acid amplification tests [NAATs]) to compare the accuracy of RIDTs, DIAs, and NAATs for children and adults suspected of having influenza. All results were compared against the gold standard, reverse transcriptase polymerase chain reaction (RT-PCR).

The new tests are simple and approved for use at the point of care by nonlaboratory staff, as are RIDTs, which have been available for decades.

DIAs had sensitivities 25.5 (95% credible interval [CrI], 17.0 - 33.4) and 23.5 (CrI, 7.7 - 37.9) percentage points higher than those for RIDTs in diagnosing influenza A and B, respectively. Rapid NAAT sensitivity beat that of RIDTs by 37.1 (CrI, 28.6 - 44.2) percentage points for influenza A and 41.7 (CrI, 28.5 - 54.0) percentage points for influenza B and that of DIAs by 11.5 (CrI, 2.9 - 19.5) and 18.2 (CrI, 6.9 to 30.6) percentage points for influenza A and B, respectively.

Pooled specificities were high for all tests at more than 98%, according to the report.

"Physicians can therefore diagnose influenza with confidence on the basis of a positive RIDT, DIA, or rapid NAAT result," the authors write.

In an accompanying editorial, Michael G. Ison, MD, professor with the Divisions of Infectious Diseases and Organ Transplantation at Northwestern University Feinberg School of Medicine in Chicago, Illinois, says the new tests will improve patient outcomes and these findings should lead to revisions in current guidelines to encourage their use.

Gold Standard's Disadvantage Is Time

Diagnosing influenza only from symptoms is tough because its forms are so varied.

With RT-PCR, specimens must be sent to a lab and results can take time.

Fast and accurate influenza diagnoses can lead to faster initiation of antiviral therapy, fewer additional tests, fewer hospital infections, and less antibiotic use.

"Current guidance recommends against the use of RIDTs to diagnose influenza in ambulatory and hospitalized settings because of poor sensitivity. The newer DIAs and rapid NAATs are simple, fast, and approved for use at the point of care by nonlaboratory staff; sensitivity approached that of RT-PCR and is markedly higher than that of RIDTs," Dr Ison writes.

Current clinical guidelines recommend antivirals for high-risk patients and those hospitalized with clinically suspected influenza before confirmation by diagnostic testing, but that is not often happening in practice, and it appears providers want a confirmed diagnosis first, Dr Ison explains.

"Most adults with influenza who receive ambulatory care do not receive antiviral therapy, whereas use of antibacterial therapy remains high," he writes.

The new tests "likely will drive more appropriate early use of antivirals, may decrease unnecessary antibacterial therapy, and may improve patient outcomes," he says.

The study authors predict that with these findings, regulators such as the US Food and Drug Administration are likely to phase out traditional RIDTs. Cost-effectiveness analyses and clinical impact studies are next for the new tests.

Many Have Already Switched

Kevin Alby, PhD, assistant professor of pathology and laboratory medicine at Perelman School of Medicine at the University of Pennsylvania in Philadelphia, told Medscape Medical News that his hospital, like many other large hospitals, started switching to rapid NAATs 2 years ago.

"The rapid NAATS are filling a gap. Around the time of the pandemic influenza, we saw that the current RIDTs were suboptimal.  There were a number of studies that showed their poor performance."

DIAs perform well with the right population, he said. Performance is much better in children, for instance, who tend to have a much higher viral burden than adults.

But the big impact will be at the clinic level, he said.

"You're not going to see academic medical centers moving toward [DIAs] replacing what they're doing in their hospital. At the clinic level, it will provide an ability to make a decision on the patient who's just coming in for an office visit and is going home" as to whether he or she needs an antiviral, Dr Alby said.

"You're OK in that setting with a lower sensitivity because the patient is otherwise well," he said, adding that hospitals will continue to use an NAAT-based method.

He praised the study for using RT-PCR as the comparator, when some studies have used culture as the comparator.

"The big thing with this study is it helps confirm what we suspected," he said.

More Independent Studies Needed

The study authors also note that industry-sponsored studies had sensitivity estimates 6.2 to 34 percentage points higher than nonsponsored studies.

That is important in interpreting their results, the authors say, because a large proportion of DIA studies in their meta-analysis (68.4%) and of NAAT studies (61.5%) reported industry ties. Those results highlight the need for more independent studies, they add.

The study was supported by the Québec Health Research Fund and by an investigator-initiated study grant from BD Diagnostic Systems. Two coauthors are recipients of career awards from the Québec Health Research Fund. Several coauthors report grants from AbbVie outside the submitted work and personal fees from Cepheid, AbbVie, and RPS Diagnostics outside the submitted work. Dr Ison reports grants from Beckman Coulter, Gilead, Janssen, Shire, Cephied; grants and personal fees from Chimerix; personal fees from Celltrion, Farmark, Genentech/Roche, and Toyama/MediVectro, Seqirus; and personal fees and other from Shionogi and GlaxoSmithKline during the conduct of the study . Dr Alby has disclosed no relevant financial relationships.

Ann Intern Med. Published online September 5, 2017. Abstract, Editorial

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