The story

The World Health Organization has called the swine flu outbreak spreading around the world a "public health emergency of international concern."

Health workers worldwide are racing to prevent what may potentially become a pandemic.

An influenza pandemic occurs when a new virus appears against which the human population has no immunity, according to the WHO.

Christine Layton, a public health expert who specializes in influenza at research institute RTI International, told CNN the swine flu has "pandemic potential."

"Unlike the avian flu that people were concerned about a few years ago, a lot more cases are occurring in a lot more different places," she said. Read full article »

Sources: World Book Online, U.S. Department of Health and Human Services

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