The fact is that epidemics and pandemics seem to hit populations during major negative social mood trends. ...when we study pandemics of the Dark Ages or the Spanish influenza epidemic that broke out during the bear market of 1917 (which year also saw intense fighting in World War I and the Communist coup in Russia), there always appears to be a bear market in force, and the extent of the epidemic tends to correlate with the size of the setback in mood. -- Bob Prechter, The Wave Principle of Human Social Behavior, Chapter 18.
There is an article to the right from Elliott Wave International that is worth reading. It is titled. "Swine Flu and Elliott Wave Analysis" and it's genesis is with the above quote from Robert Prechter's Socionomics book. (Click on "What does a rally really tell you" to access the list of articles including the Swine flu article).