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Cold and flu test aims to reduce unneeded use of antibiotics

The "xTAG Respiratory Panel" is a new test available to doctors and patients for the rapid identification of respiratory viral infections. The test relies upon advanced DNA technology to identify which one of up to 19 viruses may be responsible for a patient's respiratory symptoms. Samples are obtained using a throat swab, but the test requires an advanced technology analyzer to figure out the results.

The FDA approved the test in January 2008, and the manufacturer claims that up to 85% of viruses that cause respiratory illness are identified by the technology. At first glance, the test promises to be a boon to doctors and patients, rapidly determining the cause of upper respiratory tract infections.

A clinical trial reported later in 2008 revealed excellent test accuracy compared with standard respiratory viral testing technologies.

The test is performed by taking a swab of a patient's nose or mouth, then sending the swab for analysis with a specialized machine. Results can be ready in as little as a few hours, assuming the hospital or doctor's office has a machine on site. The test does not appear to perform instant viral testing, so is not analogous to urine dipsticks or urine pregnancy tests.

The manufacturer's web site claims the test can distinguish between bacterial and viral upper respiratory infections, but in fact these may not be mutually exclusive. Recently, prominent infectious disease specialists have pointed out that the leading cause of death in the 1918 influenza pandemic was secondary bacterial pneumonia, following the initial infection by the influenza virus. In many cases, it seems likely that an initial viral infection weakens the host immune system, allowing secondary bacterial infections.

This new test is useful to assess which respiratory virus is active in a patient's system, but it does not in any way exclude a bacterial infection. Therefore, the manufacturer's claim "Aids in determining whether a respiratory infection is viral or bacterial," lacks credibility.

The implied use of this test in the office or ER setting, then, is to distinguish which patients need an antibacterial antibiotic. I don't think the clinical data support such a use right now.

The point could be made that a patient with a documented positive viral infection on the xTAG profile could be started on rapid antiviral therapy. Problem is, our tools for treating viral upper respiratory infections are rudimentary at this time. While Tamiflu looks like it helps clear influenza 24 hours faster, it helps the most if taken early in the course of the illness. I'm not sure that the turn around time of even this new test will be short enough to encourage the use of Tamiflu in clinical real time, and even if it is, there is no evidence in the medical literature to support such an approach. We don't have a clinical trial to say, "Patients treated according to xTAG profile for viral versus bacterial infections had fewer hospital days, less antibiotic use," or some other beneficial outcome.

The use of this test to stratify patients into those who need antibiotics and those who do not need antibiotics is still not really known at this point. While the manufacturer has done a good job to prove that the test does what it says it does (i.e., identify the viruses it is supposed to), they have not done a good job determining where the test fits into clinical practice.

What would really benefit patients and doctors would be tests to figure out why some people are susceptible to viral and bacterial infections, and ways to augment the immune system to prevent infections in the first place. Interventions like Echinaceae, Zinc lozenges, Airbourne, and others have not shown success in preventing cold symptoms or shortening colds.

The bottom line treatment for upper respiratory infections remains rest, symptomatic treatments like decongestants and antihistamines, and judicious use of antibiotics in those who need them. Liberal doses of chicken soup remain mandatory.

As one colleague is fond of saying, "Without antibiotics, a cold takes about seven days to clear, and with them, about a week."

Michael Benjamin, M.D.

Hematology/Oncology West Hills, California

Check out his interactive community for physicians and patients at www.interactmd.com

 

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