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
