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H1N1 (swine) influenza



The H1N1 virus (swine flu) is a new flu virus strain that is causing illnesses in humans worldwide.

In June 2009, the World Health Organization declared a worldwide swine flu pandemic.

Alternative Names

Swine flu


Earlier forms of the H1N1 virus were found in pigs. Over time, the virus changed (mutated) and can now infect humans. Because H1N1 is a new virus in humans, your immune system cannot fight the virus very well. As a result, it has spread quickly around the world.

The largest number of H1N1 flu cases have occurred in people ages 5 - 24. Few cases, and no deaths, have been reported in people older than age 64.

The H1N1 flu virus can spread from person to person when:

  • Someone with the flu coughs or sneezes into air that others breathe in.
  • Someone touches a door knob, desk, computer, or counter with the H1N1 germs on it and then touches their mouth, eyes, or nose.
  • Someone touches mucus of a child or others while taking care of them when they are ill with the H1N1 flu virus

You CANNOT get H1N1 flu virus from eating pork or any other food, drinking water, swimming in pools, or using a hot tubs or saunas.


Symptoms of H1N1 flu infection in humans are similar to classic flu-like symptoms, which might include:

Signs and tests

If you think you have been exposed to H1N1 influenza, call your health care provider before your visit. The medical staff may want to take proper precautions to protect themselves and other patients during your office visit.

Because the H1N1 flu has become widespread, most people do not need to be tested for it when they have symptoms.

Your doctor may test you for the H1N1 flu virus by swabbing the back of the inside of your nose if:

  • You are at high risk for flu complications.
  • Others at high risk of flu complications have been in close contact with you.
  • You are very sick.

Your doctor may:

Expectations (prognosis)

The outlook depends on the severity of the infection, age, and whether there are other medical problems.

Pregnant women and young people appear more likely to get the H1N1 virus and also to have bad outcomes when they become infected.

Surprisingly, people age 65 or older have a lower risk than younger age groups.

For more information, visit:

  • Centers for Disease Control and Prevention -
  • World Health Organization -
Calling your health care provider

Anyone who is pregnant, has young children, or has a health condition such as diabetes, heart disease, asthma, or emphysema should check with their doctor when they become ill.

If you are ill and have any of the following warning signs, seek emergency medical care.

In children, emergency signs include:

  • Fast breathing or trouble breathing
  • Bluish or gray skin color
  • Not drinking enough fluids
  • Severe or persistent vomiting
  • Not waking up or not interacting
  • Being so irritable that the child does not want to be held
  • Flu-like symptoms improve but then return with fever and a worse cough

In adults, emergency signs include:


Severe illness may occur along with:

Like seasonal flu, H1N1 flu may make other chronic medical problems worse.


Most people who get H1N1 flu will likely recover without needing medical care or special antiviral medications. Check with your health care provider about whether you should take antiviral medications to treat the H1N1 flu.

Doctors may prescribe antiviral drugs to treat people who become very sick with the flu or are at high risk for flu complications. The following people may be at high risk:

  • Children younger than 5 years old, especially those younger than age 2
  • Adults 65 years of age and older
  • People with:
    • Chronic lung (including asthma) or heart conditions (except high blood pressure)
    • Kidney, liver, neurologic, and neuromuscular conditions
    • Blood disorders (including sickle cell disease)
    • Diabetes and other metabolic disorders
    • An immune system that does not work well, such as AIDS patients or cancer patients receiving chemotherapy

Other high risk people include:

  • Pregnant women
  • Anyone younger than age 19 receiving long-term aspirin therapy
  • Residents of nursing homes and other chronic-care facilities

People who may receive antiviral medications after coming into close contact with a person who is known to have, or probably is infected with the H1N1 virus, include:

  • Those at high risk for complications of influenza
  • Health care workers, public health workers, or first responders

Oseltamivir or zanamivir are the two drugs recommended for the treatment or prevention of infection with the H1N1, or swine, influenza virus.

People with H1N1 flu should also:

  • Get plenty of rest
  • Drink clear fluids (such as water, broth, sports drinks, and electrolyte beverages for infants)
  • Watch for emergency warning signs (see below)

Everyone should take these steps to prevent the flu from spreading:

  • Cover your nose and mouth with a tissue when you cough or sneeze. Throw the tissue away after using it.
  • Wash your hands often with soap and water for 15 - 20 seconds, especially after you cough or sneeze. You may also use alcohol-based hand cleaners.
  • Avoid touching your eyes, nose, or mouth, to avoid getting infected by germs.
  • Avoid close contact with sick people.
  • If you do get sick, consider staying home from work or school for 7 days after your symptoms begin, or until you have been symptom-free for 24 hours, whichever is longer.
  • Wear a facemask , if possible, when sharing common spaces with other household members


A new H1N1 vaccine is expected to be available in the fall of 2009.

The CDC recommends that these groups receive the vaccine:

  • Pregnant women
  • People who live with or care for children younger than 6 months of age
  • Health care and emergency services personnel
  • Persons between the ages of 6 months and 24 years of age
  • People from ages 25 through 64 years who are at higher risk for complications from an H1N1 infection (See Treatment section above.)

It is possible there will not be enough H1N1 vaccine at first. If this happens, the CDC recommends that these groups receive the vaccination first:

  • Pregnant women
  • People who live with or care for children younger than 6 months of age
  • Health care and emergency services personnel who have direct contact with patients or with infectious substances
  • Children 6 months through 4 years of age
  • Children ages 5 -18 who are at greater risk for complications of influenza (See Treatment section above)

Check with your doctor or nurse, local pharmacist, and local health departments to see when the vaccine will be available.

Anyone who receives this new vaccine still should also receive the seasonal flu vaccine that is released every year. You may receive both vaccines on the same day.


Novel H1N1 Flu (Swine Flu) Centers for Disease Control and Prevention. Site last updated July 31, 2009, accessed July 31 2009

Press Release: July 29, 2009 CDC Advisors Make Recommendations for Use of Vaccine Against Novel H1N1. Accessed July 31, 2009

Related Taxonomy

Review Date: 7/31/2009
Reviewed By: David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc. Also reviewed by Linda J. Vorvick, MD, Medical Director, MEDEX Northwest Division of Physician Assistant Studies, University of Washington, School of Medicine.
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The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. © 1997- 2009 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

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