Influenza (cont.)

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What are flu symptoms in adults and in children?

Typical clinical features of influenza may include

  • fever (usually 100 F-103 F in adults and often even higher in children),
  • chills,
  • respiratory symptoms such as
    • cough (more often in adults),
    • sore throat (more often in adults),
    • runny or stuffy nose (especially in children),
  • headache,
  • muscle aches,
  • fatigue, sometimes extreme.

Although nausea, vomiting, and diarrhea can sometimes accompany influenza infection, especially in children, gastrointestinal symptoms are rarely prominent. The term "stomach flu" is a misnomer that is sometimes used to describe gastrointestinal illnesses caused by other microorganisms. H1N1 infections, however, have caused more nausea, vomiting, and diarrhea than the conventional (seasonal) flu viruses.

Most individuals who contract influenza recover in a week or two, however, others develop potentially life-threatening complications like pneumonia. In an average year, influenza is associated with about 36,000 deaths nationwide and many more hospitalizations. Flu-related complications can occur at any age; however, the elderly and people with chronic health problems are much more likely to develop serious complications after the conventional influenza infections than are younger, healthier people.

Unfortunately, people may be contagious about 24-48 hours before symptoms appear and, for those who spontaneously recover, they may shed contagious viruses for about a week.

How is the flu diagnosed?

The flu is presumptively diagnosed clinically by the patient's history of association with people known to have the disease and their symptoms listed above. Usually, a quick test (for example, nasopharyngeal swab sample) is done to see if the patient is infected with influenza A or B virus. Most of the tests can distinguish between A and B types. The test can be negative (no flu infection) or positive for types A or B. If it is positive for type A, the person could have a conventional flu strain or a potentially more aggressive strain such as H1N1. However, a new test developed by the CDC and a commercial company reportedly can detect H1N1 reliably in about one hour; the test was formerly only available to the military. In 2010, the FDA approved a commercially available test that could detect H1N1 within four hours. Most of the rapid tests are based on PCR technology that identified the genetic material of the virus.

Swine flu (H1N1) and other influenza strains like bird flu or H3N2 are definitively diagnosed by identifying the particular antigens associated with the virus strain. In general, this testing is done in a specialized laboratory and is not done by many doctors' offices or hospital laboratories unless they have purchased the newest test systems. However, doctors' offices are able to send specimens to specialized laboratories if necessary.

Medically Reviewed by a Doctor on 9/23/2014

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