Medical Encyclopedia


Medical Encyclopedia

Other encyclopedia topics:  A-Ag  Ah-Ap  Aq-Az  B-Bk  Bl-Bz  C-Cg  Ch-Co  Cp-Cz  D-Di  Dj-Dz  E-Ep  Eq-Ez  F  G  H-Hf  Hg-Hz  I-In  Io-Iz  J  K  L-Ln  Lo-Lz  M-Mf  Mg-Mz  N  O  P-Pl  Pm-Pz  Q  R  S-Sh  Si-Sp  Sq-Sz  T-Tn  To-Tz  U  V  W  X  Y  Z  0-9 

H1N1 (swine) influenza

Contents of this page:

Alternative Names   

Swine flu; Influenza A

Definition    Return to top

Swine influenza is flu virus usually found in pigs. The virus occasionally changes (mutates) and becomes infectious in humans. When this happens, the disease becomes a concern to humans, who have little or no immunity against it. This means the virus has the potential to spread quickly around the world. It also may be more difficult to treat than the usual, seasonal human flu viruses.

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

Causes    Return to top

In the spring of 2009, cases of human infection with H1N1 flu were confirmed in Mexico, the United States, and many countries around the world.

The H1N1 flu virus is contagious and can spread from human to human. At this time, it is unknown how easily it can spread between people.

It is known that flu viruses can spread from pigs to people, and from people to pigs. However, you CANNOT get H1N1 flu virus from eating pork.

Human-to-human infection with the H1N1 flu virus likely occurs the same way as seasonal flu, when an infected person coughs or sneezes into air that others breathe in. People may also get infected by touching something with the virus on it, such as a door knob or counter, and then touching their mouth or nose.

You can find an updated case count of confirmed H1N1 flu infections in the U.S. at the Centers for Disease Control and Prevention (CDC) web site.

Symptoms    Return to top

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

Exams and Tests    Return to top

If you think you have been exposed to H1N1 influenza, call your health care provider before your visit. This will give the staff a chance to take proper precautions to protect them and other patients during your office visit.

If the H1N1 flu becomes widespread, there will be little need to continue testing people, so your health care provider may decide not to test for the flu virus.

Your doctor may perform the following physical exam:

Your doctor can test for the H1N1 flu virus using a nasopharyngeal swab (a swab of the back of the inside of your nose), or grow it in a culture. However, this will likely happen only if:

Treatment    Return to top

Most people who get H1N1 flu will likely recover without needing medical care. Doctors, however, can prescribe antiviral drugs to treat people who become very sick with the flu or are at high risk for flu complications. The CDC currently identifies the following people as high risk:

Other high risk people include:

Outlook (Prognosis)    Return to top

The outlook depends on the severity of the infection and the type of H1N1 influenza virus that caused it.

The H1N1 flu outbreak in Mexico has resulted in 108 confirmed deaths thus far. At least 45 deaths had been reported in the U.S. at the time of this writing. Deaths have occurred in other countries as well. Officials were preparing for more.

For more information, visit:

Possible Complications    Return to top

Severe illness may occur along with:

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

A vaccination used to treat swine flu in 1976 was associated with some cases of Guillain-Barre syndrome, a disorder that leads to nerve inflammation that causes muscle weakness.

When to Contact a Medical Professional    Return to top

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

In children, emergency signs include:

In adults, emergency signs include:

Prevention    Return to top

People who work with pigs who might be infected should use protective clothing and special breathing masks.

Other steps you can take:

Update Date: 6/17/2009

Updated by: A.D.A.M. Editorial Team: David Zieve, MD, MHA, Greg Juhn, MTPW, David R. Eltz. Previously reviewed by David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine (6/9/2009).

A.D.A.M. Logo

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician 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. Copyright 1997-2009, A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.