What Types of Flu?
Like a common cold, the flu is caused by viruses. There are four types of influenza viruses: A and B, which are most commonly associated with seasonal flu activity and epidemics; C, which is relatively rare and causes mild respiratory illness; and D, which primarily affects cattle.
Influenza A
There are many sub types of influenza A viruses, based on two proteins — hemagglutinin (H) and neuraminidase (N) — found on the surface of the viruses. Two strains of influenza A found in human beings are the H1N1 strain and the H3N2 strain.
A novel strain of influenza A (H1N1) virus, known as swine flu because it’s typically spread among pigs, led to a flu pandemic in 2009. Between April 2009 and April 2010, the CDC estimates that there were 60.8 million swine flu cases in the United States, which led to more than 274,000 hospitalizations and nearly 12,500 deaths.…
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