H1N1 influenza

Last revised by Dr Joachim Feger on 13 Oct 2021

H1N1 influenza is a strain of influenza that notably resulted in a pandemic in 2009. It was referred to colloquially as 'swine flu' due to the origin of the virus, but it was also named H1N1/09 virus. A specific but different strain of H1N1 (called H1N1 influenza A) was the cause of the Spanish flu, one of the worst global pandemics in recorded human history ref. This article refers to the disease resulting from the H1N1/09 virus.

There can be a wide spectrum of clinical syndromes ranging from being asymptomatic to fulminant viral pneumonia, respiratory failure, and death.

It is caused by a type of influenza A virus of swine origin.

It can have a variable presentation and a number of features have been described 2: In the majority of cases the chest radiograph can be normal.

Described imaging spectrum is broad, with each individual feature being non-specific on its own 2,3:

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Cases and figures

  • Case 1
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  • Case 2: causing complete white out
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  • Case 3
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  • Case 4
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