December 1, 2015
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Influenza (cont.)

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What are flu (influenza) 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, sometimes with facial flushing and/or sweating),
  • 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 appetite loss, 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, 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.

What is the incubation period for the flu?

Incubation period for the flu, which means the time from exposure to the flu virus until initial symptoms develop, typically is one to four days with an average incubation period of two days.

How long is the flu contagious, and how long does the flu last?

The flu is typically contagious about 24-48 hours before symptoms appear (from about the last day of the incubation period) and in normal healthy adults is contagious for another five to seven days. Children are usually contagious for a little while longer (about seven to 10 days). Individuals with severe infections may be contagious as long as symptoms last (about seven to 14 days). In adults, flu symptoms usually last about five to seven days, but in children, the symptoms may last longer (about seven to 10 days). However, some symptoms such as weakness and fatigue may gradually wane over several weeks.

How is the flu (influenza) 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. Most of the rapid tests are based on PCR technology that identifies 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 surface proteins or genetic material associated with the virus strain. In general, this testing is done in a specialized laboratory. However, doctors' offices are able to send specimens to specialized laboratories if necessary.

Medically Reviewed by a Doctor on 10/7/2015


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