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H1N1 Swine Flu

By Craig R. Pringle, BSc, PhD, Professor Emeritus, School of Life Sciences, University of Warwick

H1N1 swine flu is a flu infection caused by a new strain of influenza A virus.

Pigs (swine) can be infected by strains of influenza virus (see Influenza types and strains). Most strains of swine influenza virus are slightly different from those that infect people. These strains very rarely spread to people, and when they do, they very rarely then spread from person to person.

The H1N1 swine flu virus has genes from the swine, bird (avian), and human influenza viruses. H1N1 swine flu spreads easily from person to person, just like ordinary human flu. People cannot get H1N1 swine flu from eating pork and only very rarely get it from contact with pigs.

In 2009, swine flu H1N1 became so widespread that it was considered a pandemic. However, by August 2010, the number of cases had decreased so much that the pandemic was considered over.

Infection due to another strain of swine flu virus (H3N2) has occurred in children and adults in several U.S. states. Infected people had contact with apparently healthy domestic pigs, usually at agricultural fairs. Also, in a few cases, the virus may have spread from person to person.

Unlike ordinary flu, swine flu is more likely to occur and to cause death in young and middle-aged adults than in older people.


Symptoms are typically flu-like. They include fever, cough, sore throat, body aches, headache, chills, runny nose, and fatigue. Nausea, vomiting, and diarrhea are also common.

In most people, symptoms seem to develop from 1 to 5 days after exposure to the virus and continue for up to another week. People can spread the infection for about 8 days, from the day before symptoms appear until symptoms are gone.

Symptoms are usually mild but can become severe, leading to pneumonia or respiratory failure. The infection can make chronic disorders (such as heart and lung disorders and diabetes) worse and, during pregnancy, can cause complications (such as miscarriage or premature birth). Also at high risk of complications are children under 5 years old and people with kidney or liver disorders or a weakened immune system due to drugs or disorders such as AIDS. Severe complications can develop and progress rapidly—sometimes, even in young, healthy people.


  • Testing of a sample taken the nose or throat

Doctors may take samples of secretions from the nose and mouth. A test that can confirm H1N1 infection can be done.


People with flu-like symptoms should stay home, cover their mouth and nose with a tissue when sneezing or coughing, wash their hands frequently, and use an alcohol-based hand sanitizer.

People who have been in close contact with someone who has swine flu may be given antiviral drugs.

There is a vaccine for swine flu.


  • Rest and plenty of fluids

  • Relief of symptoms

  • Sometime antiviral drugs

People should see a doctor immediately if they have severe vomiting, shortness of breath, chest or abdominal pain, or sudden dizziness or confusion.

Children should be taken to a doctor immediately if they have blue lips or skin, are not drinking enough fluids, are breathing rapidly or with difficulty, are unusually drowsy or irritable (including not wanting to be held), or have a fever with a rash.

If people at high risk of severe complications (including children under 5 years old) or pregnant women have even mild symptoms, a doctor should be contacted.

Also, if a fever and a worse cough develop after flu-like symptoms disappear in any person, a doctor's attention is required.

Treatment focuses on relieving symptoms. For example, acetaminophen can relieve fever and aches. Getting enough rest and drinking plenty of fluids can help.

The antiviral drugs oseltamivir or zanamivir may be used if people are at risk of complications or have severe symptoms. These drugs are most effective when started within 48 hours after symptoms appear. In the United States, most people have recovered from H1N1 swine influenza fully without taking these drugs.

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