In the last century, three influenza pandemics have swept the globe. In 1918, the first pandemic (sometimes referred to as the "Spanish Flu") killed over 500,000 Americans and more than 20 million people worldwide. One-third of the U.S. population was infected, and average life expectancy was reduced by 13 years. Pandemics in 1957 and 1968 killed tens of thousands of Americans and millions across the world. Scientists believe that viruses from birds played a role in each of those outbreaks.