H1N1 Influenza
(H1N1 Flu Virus · Influenza A (H1N1) · Human Swine Flu · Swine Flu)
In this condition factsheet:
The Facts on H1N1 Influenza
H1N1 influenza is a contagious respiratory disease that causes symptoms of seasonal influenza in people.
The name "swine flu" was initially used to describe this type of influenza because laboratory tests showed that this strain of flu virus was made up of genes that were very similar to the ones that caused influenza among pigs (swine). Just like humans, pigs can get the flu. However, we now know that the H1N1 flu virus is made up of genes from several different flu viruses that normally circulate among pigs, birds, and humans. This strain was the most common cause of influenza in 2009, when it caused disease worldwide ("pandemic").
Causes of H1N1 Influenza
H1N1 flu is caused by an influenza A virus. 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 influenza A 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. Influenza is generally not spread by eating food or drinking water.
Symptoms and Complications of H1N1 Influenza
The various strains of influenza A virus infection produce identical symptoms. People may experience:
- body aches
- chills
- cough
- fatigue
- fever
- headache
- loss of appetite
- sore throat
Some people with H1N1 flu virus have also reported vomiting and diarrhea.
The severity of symptoms can vary from mild to severe and sometimes require hospitalization. In some cases, severe complications such as pneumonia and respiratory failure can cause death. Like the seasonal flu, H1N1 flu may worsen existing chronic medical conditions.
