Causes of H1N1 Influenza
H1N1 flu is caused by a virus. The most common subtype, or strain, is influenza type A H1N1, and this subtype has also caused infection in people. The letters H and N in the subtype name stand for proteins found on the surface of the virus, which are used to distinguish between different subtypes.
Influenza viruses are constantly changing their genes, a process called mutation. When a swine flu virus is found in humans, it is said to have "jumped the species barrier." This means that the virus has mutated in a way that allows it to cause the condition in humans. Because humans have no natural protection or immunity to the virus, they are likely to become ill. The H1N1 flu virus is made up of genes from flu viruses that normally cause influenza in pigs, birds, and humans.
H1N1 flu virus is contagious. Person-to-person transmission of H1N1 flu virus occurs, and the virus is easily spread among people. It is believed that it is spread the same way as regular seasonal influenza. A person infected with H1N1 flu virus can infect others starting 1 day before symptoms develop and up to 7 or more days after becoming ill.
Influenza is spread from person to person when the virus enters the body through the eyes, nose, and/or mouth. Coughing and sneezing release the germs into the air, where they can be breathed in by others. The virus can also rest on hard surfaces like doorknobs, ATM buttons, and counters. A person who touches these surfaces with their hands and then touches their eyes, mouth, or nose can become infected with the virus. You cannot get infected with the H1N1 flu virus from eating pork products that have been properly cooked - heated through to 71°C (160°F).