What is swine influenza?
Swine influenza (also called "swine flu" or "pig flu") is a group of influenza viruses that usually infects pigs. Infections in humans are uncommon. The current flu that is infecting people is a new strain of influenza A/H1N1 of swine origin. It is not certain how it developed.

Is there only one type of swine flu virus?
No. Like all human influenza viruses, swine influenza viruses change constantly. There are four main influenza type A virus "subtypes" which have been isolated in pigs: H1N1, H1N2, H3N2, and H3N1. The most common strain found in pigs is the H1N1 virus. However, sometimes pigs can be infected with more than one virus type at a time. This gives the genes from the viruses an opportunity to mix and "reassort" to form a new virus.

Can humans get sick with swine flus?
Yes. Human infections are uncommon, but have occurred in the past. Human infections with swine flu is more common in individuals who have direct exposure (close contact) with pigs. The new strain that began circulating in April 2009 can move from person to person, and so more people than usual are being infected.

Can swine flus be spread from human-to-human?
Yes, sometimes. Historical evidence shows human-to-human transmission of swine flu has occurred. In 1988, in Wisconsin USA, multiple human infections were reported after an apparent outbreak of swine flu in pigs. No community outbreak was ever officially announced, but there was serological evidence to show that the patient (who had direct contact with infected pigs) transmitted the virus to the treating health care workers.

How does swine flu spread?
Typically, swine flu can be spread from pigs to humans, and from humans to pigs. That is more likely to occur when people have close contact (or are in close proximity) with infected pigs.

Can I catch flu from eating pork or pork products?
No. Flu viruses cannot be transmitted by food. It is safe to eat pork and pork products that have been properly handled and/or sufficiently cooked. Cooking pork to an internal temperature of 160°F (or 72°C) kills the flu virus as well as other viruses and bacteria.

Are swine H1N1 viruses the same as human H1N1 viruses?
No. Swine flu H1N1 viruses are genetically different from human H1N1 strains.

For more information see the CDC page on swine flu in pigs and people