No disease the world has ever known even remotely resembles the great influenza epidemic of 1918. Presumed to have begun when sick farm animals infected soldiers in Kansas, spreading and mutating into a lethal strain as troops carried it to Europe, it exploded across the world with unequaled ferocity and speed. It killed more people in twenty weeks than AIDS has killed in twenty years; it killed more people in a year than the plagues of the Middle Ages killed in a century. Victims bled from the ears and nose, turned blue from lack of oxygen, suffered aches that felt like bones being broken, and died. In the United States, where bodies were stacked without coffins on trucks, nearly seven times as many people died of influenza as in the First World War.