FREE subscriptions for doctors and students... click here
You have 3 more open access pages.
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.
Last reviewed 01/2018