Diagnosing the flu on the fly: Point-of-care tests for Influenza

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By Barbara Greenwood Dufour

Most of us take measures during “flu season” to avoid catching the influenza virus (the flu), such as getting the flu shot and using proper handwashing, sneeze, and cough etiquette. But each year, an estimated 10 to 20 per cent of Canadians become infected with influenza. Most will get better by staying at home to rest. But, for others, influenza can be much more serious — even deadly.

In Canada, about 12,000 people are hospitalized and 3,500 die as a result of serious complications from the influenza virus every year. Those at a higher risk of developing complications include very young children, people over 65 years of age, pregnant women, and people with chronic illnesses or weakened immune systems. When these people get the flu, they sometimes need antiviral medications to recover.

For patients at high risk of flu complications who are experiencing flu symptoms, a lab test is sometimes used to confirm the diagnosis before antivirals are prescribed. Flu symptoms can be similar to those caused by a bacterial infection. Although lab tests are very reliable, they can take several hours to several days for results. Because of this delay, clinicians often send patients home on antibiotics, just in case the test comes back negative. However, antibiotics are not effective at treating the flu virus, and overuse of antibiotics can lead to antibiotic resistance.

But what if a flu test provided results to the clinician before the patient even leaves the office? A number of newer influenza testing devices have recently been developed that provide test results in less than 30 minutes right in the doctor’s office — at the point of care. This alternative to the conventional lab test could be used in other settings as well, such as a nursing home or at a pharmacy.

How effective are these tests at improving appropriate prescribing? Are they reliable? The CADTH Horizon Scanning service recently looked at the available evidence to find out. CADTH is an independent agency that finds, assesses, and summarizes the research on drugs, medical devices, tests, and procedures to find out what the evidence says. Its Horizon Scanning service identifies new and emerging technologies that are likely to have a significant impact on health care in Canada and reports on what is known so far about these technologies. The CADTH Horizon Scanning report Point-of-Care Testing for Influenza is focused on a specific test (cobas Liat System, not currently available in Canada) but, as part of its assessment, looked at other rapid influenza tests as well and provides some insight on this topic.

There are two types of rapid influenza tests: rapid antigen tests that detect the presence of influenza infection, and rapid reverse transcription-polymerase chain reaction (RT-PCR) tests that detect the influenza virus’s RNA. One rapid RT-PCR test available in Canada is the Alere i Influenza A & B. Rapid antigen tests available in Canada include QuickVue Influenza A+B, FebriDx, BD Veritor System, and RAMP Flu A + B.

CADTH found a few studies that suggest rapid influenza tests do result in more appropriate prescribing.  Although the studies are small, they indicate that when patients test positive for the flu at the point of care, clinicians are less likely to prescribe an antibiotic. Interestingly, this doesn’t seem to be the case with children — according to a study involving pediatric patients in the emergency department with acute respiratory infections, rapid testing didn’t reduce antibiotic use.

When CADTH looked for the available evidence on the accuracy of rapid influenza tests compared with lab tests, it found that they don’t appear to perform quite as well. This means that patients who test negative for the flu might in fact have the flu and need antivirals. On the other hand, those who test positive for the flu at the point of care might be less likely to be prescribed antibiotics “just in case.” But, of the two types of rapid tests, it seems that the rapid RT-PCR test (Alere i Influenza A & B) might be more accurate for detecting the flu virus. Until evidence shows that rapid tests are as reliable as traditional tests, however, it’s unclear to what extent they could replace conventional lab testing.

If you’d like more information about CADTH’s Horizon Scanning report on point-of-care tests for influenza — or on a variety of other new and emerging devices, procedures, diagnostics, and other health interventions — visit cadth.ca/Horizon-Scanning. To learn more about CADTH, visit cadth.ca, follow us on Twitter @CADTH_ACMTS, or talk to the Liaison Officer in your region: cadth.ca/Liaison-Officers. To suggest a new and emerging technology for CADTH review, email us at HorizonScanning@cadth.ca.

Barbara Greenwood Dufour is a Knowledge Mobilization Officer at CADTH.

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