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Questions & Answers

2009 H1N1 Flu ("Swine Flu") and You
November 5, 2009 5:00 PM ET


2009 H1N1 Flu

What is 2009 H1N1 (swine flu)?
2009 H1N1 (sometimes called “swine flu”) is a new influenza virus causing illness in people. This new virus was first detected in people in the United States in April 2009. This virus is spreading from person-to-person worldwide, probably in much the same way that regular seasonal influenza viruses spread. On June 11, 2009, the World Health Organization (WHO) signaled that a pandemic of 2009 H1N1 flu was underway.

Why is 2009 H1N1 virus sometimes called “swine flu”?
This virus was originally referred to as “swine flu” because laboratory testing showed that many of the genes in this new virus were very similar to influenza viruses that normally occur in pigs (swine) in North America. But further study has shown that this new virus is very different from what normally circulates in North American pigs. It has two genes from flu viruses that normally circulate in pigs in Europe and Asia and bird (avian) genes and human genes. Scientists call this a "quadruple reassortant" virus.

2009 H1N1 Flu in Humans

Are there human infections with 2009 H1N1 virus in the U.S.?
Yes. Human infections with 2009 H1N1 are ongoing in the United States. Most people who have become ill with this new virus have recovered without requiring medical treatment.
CDC routinely works with states to collect, compile and analyze information about influenza, and has done the same for the new H1N1 virus since the beginning of the outbreak. This information is presented in a weekly report, called FluView.

Is 2009 H1N1 virus contagious?
The 2009 H1N1 virus is contagious and is spreading from human to human.

How does 2009 H1N1 virus spread?
Spread of 2009 H1N1 virus is thought to occur in the same way that seasonal flu spreads. Flu viruses are spread mainly from person to person through coughing or sneezing by people with influenza. Sometimes people may become infected by touching something – such as a surface or object – with flu viruses on it and then touching their mouth or nose.

Can I get 2009 H1N1 more than once? Nov 5
Getting infected with any influenza virus, including 2009 H1N1, should cause your body to develop immune resistance to that virus so it's not likely that a person would be infected with the identical influenza virus more than once. (However, people with weakened immune systems might not develop full immunity after infection and might be more likely to get infected with the same influenza virus more than once.) However, it's also possible that a person could have a positive test result for flu infection more than once in an influenza season. This can occur for two reasons:

1. A person may be infected with different influenza viruses (for example, the first time with 2009 H1N1 and the second time with a regular seasonal flu virus. Most rapid tests cannot distinguish which influenza virus is responsible for the illness. And,
2. Influenza tests can occasionally give false positive and false negative results so it's possible that one of the test results were incorrect. This is more likely to happen when the diagnosis is made with the rapid flu tests. More information about flu diagnosis is available at http://www.cdc.gov/h1n1flu/diagnosis/.