Tell me the history of swain flu.
Before the current spate of cases, there were 12 known transmissions of swine flu to humans across the United States from 2005 to February this year.
This was up from just one person contracting swine flu \"every one or two years\" across the US up to 2005.
\"Swine flu viruses do not normally infect humans, however, sporadic human infections with swine flu have occurred,\" says the United States\' Centers for Disease Control and Prevention (CDC).
The cases commonly involved pig industry workers, the CDC says, or people who came into close contact with infected pigs at country fairs.