ALL epidemics are different in their own way, and the current swine flu outbreak — which by Friday had sickened 141 people in 19 states, and caused deaths and illness in Mexico and 13 other countries — is no exception. Yet, as you can see from the chart below, which provides details on a selected handful of epidemics in American history, all outbreaks share certain themes. While some of these events killed many thousands and others affected only a few, in each case public health officials felt a grave threat was imminent and did what they could using the science...