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Normal lung anatomy
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Influenza
Influenza
OverviewSymptomsTreatmentPrevention

Influenza

Definition:
A contagious viral infection of the nose, throat and lungs which often occurs in the winter.

Alternative Names:
Flu; Influenza A; Influenza B; Influenza C

Causes, incidence, and risk factors:

Influenza is a common viral infection. It is caused by three viruses - Influenza A, B and C. Type A is usually responsible for the large outbreaks and is a constantly changing virus. New strains of Type A virus develop regularly and cause new epidemics every few years. Type B causes smaller outbreaks, and Type C usually causes mild illness. In the United States, infection with influenza A and B leads to 20,000 deaths and more than 100,000 hospitalizations each year. Influenza is transmitted from person to person via contagious droplets that are spread when an infected person sneezes or coughs.

Certain individuals are at higher risk from complications of influenza and therefore should be vaccinated:

  • People aged 50 or older
  • People with conditions such as the following:
    • diabetes
    • conditions affecting the heart
    • conditions affecting the lungs (such as asthma)
    • conditions affecting the kidneys
  • Health care workers
  • Anyone with a weakened immune system (such as transplant recipients or people with HIV)

Supplies of vaccine are limited each year, but after high-risk people have been vaccinated, anyone desiring protection can request vaccination.



Review Date: 3/1/2002
Reviewed By: Rocio Hurtado, M.D., Infectious Diseases Division, Massachusetts General Hospital and Brigham and Women's Hospital, Boston, MA and Philip L. Graham III, M.D., Department of Pediatrics, Children's Hospital of New York, Columbia University, New York, NY. Review provided by VeriMed Healthcare Network.

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