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2288 pages added, reviewed or updated during the last month (last updated: 19/4/2021)


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influenza

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Influenza or “flu” is an upper respiratory tract infection caused by a virus belonging to the Orthomyxoviridae family (1).

There are three serotypes - A, B and C out of which A and B are responsible for epidemics of respiratory illness

  • type A
    • causes outbreaks in most years and is the usual cause of epidemics (2)
    • is further divided into subtypes according to the two proteins on the external coat , the hemagglutinin (H1–H16) and the neuraminidase proteins (N1–N9) (3)
  • type B
    • causes less severe disease and milder outbreaks
    • but in children the severity may be similar to that seen in influenza A infection (2)
    • generally responsible for regional outbreaks (4)
  • type C
    • causes a milder infection that does not cause epidemics
Seasonal influenza consists at present of variable mixes of type A and B influenza viruses (3).

Epidemics of influenza occur mainly in the winter months. Profound changes in the viral antigens result in larger outbreaks called pandemics.

Influenza is usually a self-limiting disease but significant mortality is observed in those with chronic chest or cardiovascular disease.

Reference:

Last reviewed 01/2018

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