Optimal Influenza Treatment: Understand Influenza Testing

In a good year, approximately 9 million Americans develop influenza. On the typical bad year, 36 million Americans hack and cough their way through 3 or more days of debilitating flu. Early in the infection's course, prescribers can use one of a number of FDA-approved agents (amantadine and rimantadine for influenza A; oseltamivir phosphate, peramivir, and zanamavir for circulating influenza viruses) to treat patients who have the flu. One barrier to treatment has been determining if the patient actually has influenza, and how long he or she has had it.

The journal Medical Laboratory Observer discusses the role of testing and influenza therapy decision-making. Acknowledging that antiviral therapy must be started within 24 hours of symptom onset, the article stresses that rapid testing is reasonable when clinicians suspect influenza.

Early treatment accomplishes a number of things. First, it can alleviate the magnitude of symptoms, and shorten the duration of active illness. More importantly, it can minimize other people's exposure and stem the spread of the infection.

Traditional testing methods for influenza generate results in 4 to 5 days, which is outside the window of opportunity for treatment.

Rapid influenza diagnostic tests (RIDT) eliminate the need to send a culture to the lab. Easy and affordable, clinicians could run these tests either in the laboratory or at point-of-testing. Results are available in a few minutes. And, these tests have remarkable specificity which eliminates the need to send a culture to the lab for confirmation.

The one area where RIDT needs improvement is sensitivity. Health care policy makers began to understand the true impact of its low sensitivity in 2009 when the novel H1N1 influenza epidemic occurred. RIDT had low sensitivity for H1N1, resulting in many false negative results.

An alternative to RIDT is rapid molecular assay technology. This type of test lyses the viral membrane to expose RNA. Several rapid molecular assay tests are now available and approved. They can deliver results in about 13 minutes. They cost more than RIDT tests, but advocates for this type of testing argue that it improves antibiotic stewardship and reduces related rates of Clostridium difficile infection.

The author concluded that even the best tests are unreliable if the clinician has poor technique when it comes to sampling. It's imperative to read the directions and follow the sampling procedure exactly. False negatives increase when influenza is not circulating and the most reliable results occur during periods of outbreaks.

Reference

Moore N. Rapid molecular testing is having an increasing impact on influenza therapy decisions. Medical Laboratory Observer. September 2017. Available at https://www.mlo-online.com/rapid-molecular-testing-increasing-impact-influenza-therapy-decisions. Accessed October 1, 2017.