Pandemics are epidemics that occur on a global scale. They generally result from the emergence of an influenza A virus that is novel for the human population. The hallmark of pandemic influenza is excess mortality--the number of deaths observed during an epidemic of influenza-like illness in excess of the number expected. During this century, pandemics occurred in 1918, 1957 (Asian flu), and 1968 (Hong Kong flu). The 1918 influenza outbreak is regarded as the worst in human history--it killed up to 40 million people world wide.

The outbreak started in the United States at an army base in the Midwest and then spread to Europe and other parts of the world. This epidemic was different from most others because it preyed heavily upon the 20 to 40 year old age group, which was normally the most healthy and resistant to disease.

It all started on March 11, 1918 at an army camp in...