2009 H1N1 influenza: a pandemic

The first cases of 2009 pandemic influenza A (H1N1) virus infection were documented in March 2009 and have subsequently caused a worldwide outbreak. The World Health Organization declared the first phase 6 global influenza pandemic of the century on June 11, 2009. As of November 2009, more than 47 million people in the United States have been infected and there have been more than 213,000 H1N1-related hospitalizations and approximately 10,000 H1N1-related deaths. The majority of illness is reported in the 18-64 years age group. The risk of illness, hospitalization, and death related to 2009 H1N1 is very age-specific and very different from seasonal influenza.