Diagnosis of Flu

Influenza Diagnosis

Currently, most influenza strains go undiagnosed or are identified in a laboratory miles from a doctor’s office. If the strain is diagnosed, the time between a throat swab and a final read out can be days, if not weeks.

As the risk of a flu pandemic increases, healthcare professionals must be able to quickly distinguish one flu strain from another. Therefore, NIAID supports research to design diagnostics that are faster, more accurate, more cost-effective, and more portable.

New technologies being pursued include those that examine influenza viruses at the molecular level. By examining the genetic makeup of influenza viruses, such tests could identify both the virus type and subtype simultaneously.

Source: NIAID (NIH)1

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Influenza can be difficult to distinguish from respiratory illnesses caused by other pathogens on the basis of signs and symptoms alone. The positive predictive value of clinical signs and symptoms for influenzalike illness (fever with either cough or sore throat) for laboratory-confirmed influenza virus infection is 30%-88%, depending on the level of influenza activity.

Diagnostic tests available for influenza include viral culture, rapid influenza diagnostic tests (RIDTs), immunofluorescence assays, and RT-PCR. Most patients with clinical illness consistent with uncomplicated influenza in an area where influenza viruses are circulating do not require diagnostic testing for clinical management. Patients who should be considered for influenza diagnostic testing include the following:

  • Hospitalized patients with suspected influenza
  • Patients for whom a diagnosis of influenza will inform decisions regarding clinical care, especially those with medical conditions that place them at high risk of complications
  • Patients for whom results of influenza testing would affect infection control or management of close contacts, including other patients, such as in institutional outbreaks or other settings (cruise ships or tour groups, for example)

The sensitivity of RIDTs varies but is substantially lower than for RT-PCR or viral culture. The sensitivity of RIDTs to detect animal-origin influenza viruses, including avian influenza viruses, can vary by test type and virus subtype. Therefore, a negative RIDT result does not rule out influenza virus infection, and health care providers should not rely on a negative RIDT result to make decisions about treatment.

Source: CDC Yellow Book 20162

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  1. Source: NIAID (NIH): niaid.nih.gov/ diseases-conditions/ influenza-diagnosis
  2. Source: CDC Yellow Book 2016: cdc.gov/ travel/ yellowbook/ 2016/ infectious-diseases-related-to-travel/ influenza

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Note: This site is for informational purposes only and is not medical advice. See your doctor or other qualified medical professional for all your medical needs.