By the bioMérieux Connection Editors
Over the last decade, rapid diagnostics for flu and other respiratory illnesses have become much more readily available, allowing physicians to treat patients with respiratory symptoms more quickly and accurately. Some rapid flu tests can not only help determine whether a patient has the flu, but also the type of virus, which provides important epidemiologic information. The CDC states that, “Influenza virus isolates are essential for determining the match between circulating influenza virus strains and those virus strains contained in the vaccine and for aiding in the selection of new vaccine strains.”
However, while rapid influenza diagnostic tests (RIDTs) can provide valuable information in as little as 15 minutes, “RIDTs vary in terms of sensitivity and specificity when compared with viral culture or RT-PCR,” according to the CDC. Sensitivities range from approximately 50% to 70%, and specificities approximately 90% to 95%.
Additionally, the predictive value of RIDTs depends on flu prevalence in the patient population. False-positive and true-negative test results are more likely to occur when disease prevalence is low, while false-negative and true-positive results are more likely when disease prevalence is high.
An addition or alternative to RIDTs that may offer advantages, particularly for patients with additional risk factors such as a compromised immune system, is a multiplex PCR (polymerase chain reaction) panel. The first FDA-approved multiplex PCR panel for a large number of respiratory pathogens became available in 2008, and since then, there have been many additions to the market.
Multiplex PCR tests allow physicians to take a syndromic approach to diagnosis, rather than trying to infer a specific pathogen or pathogens up front. In an article for the Journal of Clinical Microbiology (JCM), Dr. Paul Shreckenberger discusses data from his laboratory at Loyola University Medical Center, which showed that, “In the period October 2013 through September 2014, our laboratory identified 1,528 positive specimens, of which only 242 (15.8%) were infections caused by influenza A. An additional 1,286 respiratory pathogens were detected using our multiplex PCR assay.”
Although multiplex PCR panels are typically more costly, that cost is decreasing and can be more than offset by the savings and efficiencies achieved by rapid diagnosis. The JCM article points out in its conclusion that, “Cost assessments of panel tests need to consider the overall cost or cost savings to the health care system, not just the cost of the test to the microbiology laboratory. Factors to consider include decreased use of antibiotics, decreased ancillary testing, decreased length of stay in the hospital or emergency department, and time off work.”
Ultimately, the value of multiplex panels depends on the clinical situation, but they have the potential to transform the way physicians manage patients with infectious diseases.
Opinions expressed in this article are not necessarily those of bioMérieux, Inc.