Medical Conditions - H1N1 Influenza

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H1N1 Influenza

(H1N1 Flu Virus, Influenza A (H1N1), Human Swine Flu, Swine Flu)

The Facts

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”).


H1N1 flu is caused by a 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

The various strains of influenza A virus infection produce the same kinds of 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.

Making the Diagnosis

A doctor can perform laboratory tests that help identify the flu virus. If you have recently travelled to an area of the world where there is an H1N1 flu outbreak in humans and you have any of the symptoms of the flu, you should see your doctor. Be sure to tell the doctor where you have visited. Before you see your doctor, call them ahead of time so that they can prepare for your visit.

Treatment and Prevention

The H1N1 strain is included in the seasonal influenza vaccine. There are also medications available to help in the prevention and treatment of H1N1 flu. These are called antiviral medications. There are 2 classes available: M2 inhibitors (e.g., amantadine*) and neuraminidase inhibitors (e.g., oseltamivir, zanamivir).

Most people with previously reported H1N1 flu have been able to recover fully without medical attention and without antiviral medications. However, the occurrence of outbreaks indicate that treatment with antivirals may be needed, especially for people who have moderate-to-severe symptoms and for people who are at risk for complications of influenza (e.g., people with underlying medical conditions).

For people who are sick, help yourself get better and prevent the spread of the virus by doing the following:

  • Stay at home if you are sick. Do not go to work or school.
  • Stay at least 1 metre away from other people.
  • Rest and drink plenty of fluids.
  • Cover your mouth and nose with a tissue when coughing or sneezing. Throw your used tissue in the garbage. If you do not have tissue available, cover your sneezes with your sleeve or hands. Wash your hands thoroughly afterwards.
  • Wash your hands regularly with soap and water. Make sure to wash your hands with soap for at least 15 seconds. Use an alcohol-based hand sanitizer if you don’t have access to soap and water.

There are ways to protect yourself from catching the H1N1 flu virus. By far, the most effective preventative measure is to get the influenza vaccine just before the annual flu season (generally November through April in North America). People who are travelling in areas where an H1N1 flu virus outbreak has occurred need to take special precautions to reduce the chance of exposure to the H1N1 flu virus. Here are some tips to prevent flu:

  • Avoid close contact with people who are sick and who have symptoms of H1N1 flu (e.g., fever, cough).
  • Wash your hands with soap and water frequently and thoroughly. To ensure proper sanitization, you should wash your hands with soap for at least 15 seconds. Use alcohol-based sanitizers if handwashing is not convenient.


*All medications have both common (generic) and brand names. The brand name is what a specific manufacturer calls the product (e.g., Tylenol®). The common name is the medical name for the medication (e.g., acetaminophen). A medication may have many brand names, but only one common name. This article lists medications by their common names. For information on a given medication, check our Drug Information database. For more information on brand names, speak with your doctor or pharmacist.

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