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Outpatient Visits for Influenza-like-Illness are Above the National Baseline: Minimize False Rapid Influenza Diagnostic Tests

Influenza viurs

Outpatient Visits for Influenza-like-Illness are Above the National Baseline: Minimize False Rapid Influenza Diagnostic Tests

According to the Centers for Disease Control and Prevention, influenza activity is rising in the U.S. at this time. Outpatient visits for influenza-like-illness are above the national baseline and activity is expected to increase further in the coming weeks.  In addition to a yearly flu vaccine for everyone 6 months and older the CDC also recommends prompt diagnosis and treatment with influenza antiviral drugs.

One tool for health care professionals to aid in diagnosis are Rapid Influenza Diagnostic Tests (RIDTs). RIDTs can be used to help with diagnostic and treatment decisions for patients. However, due to the limited sensitivities of these tests, the results of RIDTs do not exclude influenza virus infection in patients with signs and symptoms suggestive of influenza. Therefore, if clinically indicated, antiviral treatment should not be withheld from patients with suspected influenza, even if they test negative by RIDT, and further influenza testing of respiratory specimens by molecular assays may be indicated.

Advantages of RIDTs

  • Produce quick result in less than approximately 15 minutes, simple to perform
  • Some RIDTs are cleared for office/bedside use. RIDTs that have been CLIA waived can be used in settings that include point-of-care.

Disadvantages of RIDTs

  • Sub-optimal test sensitivity, false negative results are common, especially when influenza activity is high
  • Sensitivity of RIDTs to detect influenza B viral antigens is lower than for detection of influenza A viral antigens.
  • Although specificity is high, false positive results can also occur, especially during times when influenza activity is low.
  • Some RIDTs distinguish between influenza A or B viruses while others do not. RIDTs that provide results on the type of influenza virus (e.g., influenza A or B virus), do not provide information on influenza A virus subtype [e.g., A(H1N1)pdm09 versus A(H3N2)] or specific virus strain information (e.g., degree of similarity to vaccine strains). RIDTs cannot distinguish between seasonal influenza A virus infection and novel influenza A virus infection (due to infection with avian or variant influenza A viruses).

Strategies to minimize false RIDT results include:

  • Collecting specimens as early in the illness as possible (ideally less than 4 days from illness onset).
  • Following manufacturer’s instructions, including acceptable specimens, and handling.
  • Following-up negative results with confirmatory tests (RT-PCR or viral culture) if a laboratory-confirmed influenza diagnosis is desired.

Additionally, testing is not needed for all patients with signs and symptoms of influenza to make antiviral treatment decisions. Once influenza activity has been documented in the community or geographic area, a clinical diagnosis of influenza can be made for outpatients with signs and symptoms consistent with suspected influenza, especially during periods of peak influenza activity in the community.

The Joint Commission (TJC) offers the course, Strategies for Improving Rapid Influenza Testing and Treatment in Ambulatory Settings (SIRAS), to help healthcare providers to ensure reliable use of RIDTs. The course will assist providers to:

  • Learn when to order a Rapid Influenza Diagnostic Test (RIDT)
  • Understand how to interpret RIDT results
  • Understand how to use local epidemiological information, clinical presentation and RIDT results to assist with the diagnosis and treatment of influenza
  • Learn how to properly collect respiratory samples for influenza testing

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