Influenza Diagnosis

Time is of the essence when diagnosing and treating influenza. Rapid influenza diagnostics that enable medical professionals to quickly determine if a patient has the flu and if so, which strain and whether it may be resistant to antiviral drugs can ensure that the patient receives the most appropriate care.

Current Influenza Diagnostic Techniques

Influenza can be difficult to diagnose, because its most visible symptoms (fever, cough, aches) are similar to many other common illnesses. Healthcare providers have several different ways to determine if a patient has the flu. Rapid influenza diagnostic tests can detect influenza in under 30 minutes, using swabs or samples of secretions taken from a patient’s nose or throat. However, these tests can yield false positive or false negative results, and they may not be able to indicate which specific strain of flu the patient has.

Other testing methods can be more accurate, but may require healthcare providers to send samples of a patient’s throat cells, saliva, or other biological materials to a lab. These methods often cultivate the virus itself, or the RNA inside it, to allow for a more accurate evaluation of the virus’s characteristics and origin. It can take days or even longer for a healthcare provider to receive results from these tests, and the resulting delay in diagnosis can make treatment less effective. However, these testing methods still have value for epidemiological purposes. Common testing methods include viral culture, rapid antigen testing and rapid molecular assays using reverse transcription polymerase chain reaction (PCR). 

NIAID Flu Diagnostics Research

Because different strains of flu respond differently to available drugs, healthcare providers must be able to quickly distinguish one flu strain from another. NIAID supports research to design diagnostics that are faster, more accurate, more cost-effective, and more portable. Specifically, NIAID has worked to develop diagnostic platforms capable of examining influenza viruses at the molecular level and rapidly distinguishing flu type A and flu type B and the wide variety of flu type A virus subtypes. For instance, NIAID-funded researchers are working on a paper-strip test which might someday help healthcare providers accurately diagnose influenza quickly and cheaply, even in remote, isolated locations. NIAID has supported several diagnostics that were cleared by the FDA for use in flu detection, including:

  • The Lab-in-a-Tube (Liat) influenza A/B assay, which can detect and differentiate influenza A and B strains in healthcare settings within 20 minutes. The assay was originally developed by Massachusetts-based IQuum; Roche acquired the company in 2014.
  • The FilmArray diagnostic system, developed by BioFire Diagnostics, LLC, based in Utah, which uses PCR to detect viruses, bacteria, yeast and parasites in roughly an hour. Specifically, the FilmArray respiratory panel, which is designed for use in hospital laboratories and point-of-care settings, can differentiate flu strains.
  • The Xpert Flu A/B diagnostic, developed by Sunnyvale, Calif.-based Cepheid, which can rapidly detect and differentiate flu type A from flu type B and identify the 2009 H1N1 flu strain.
  • The QuickVue Influenza Test, developed by San Diego-based Quidel, which detects and differentiates flu type A and flu type B based on nasal or nasopharyngeal swabs or nasal specimens.

Today, researchers are developing clinical assays to determine whether influenza viruses are sensitive to neuraminidase inhibitors, a class of antiviral drugs that inhibit release of influenza virus from infected cells. Diagnostics that enable healthcare professionals to quickly distinguish one flu strain from another at the point of patient care and to detect resistance to antiviral drugs would ensure that patients receive the most appropriate care.

Content last reviewed on April 10, 2017