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) announced that a pandemic of 2009 H1N1 flu was underway.
“Pandemic” means that an infectious disease, in this case Swine Flu, has spread all over the world in a very short period of time and is continuing to infect people. Pandemics due to influenza occur about 3-5 times per century, and are generally much more severe than routine “seasonal” flu. The worst pandemic in world history was caused by the “Spanish Flu” of 1918, which caused the deaths of 500,000 Americans and 50-100 million people throughout the world. This pandemic so far has been much less deadly.