A contagious respiratory infection that frequently occurs in epidemics. The term “flu” is also applied to various forms of viral gastroenteritis, com¬monly known as stomach or intestinal flu, which are unrelated to true respiratory influenza. This article will deal only with the respiratory disease.
History. The so-called “English Sweat” of the 16th century was the first definitely identifiable influenza epidemic. Seemingly, pandemics, or worldwide epidemics, of influenza occur in 20-year to 50-year cycles with minor local epidemics in between. Major pandemics occurred in 1627, 1729, 1788, 1830, 1847, 1872, 1890, 1918, 1957, and 1968. The 1918 pandemic, after World War I, was the worst on record. It killed 10,000,000 more people than the war; in the United States, 500,000 people died. Since World War II vaccines have helped contain flu epidemics and thereby reduce mortality. Mortality was very low in the 1957 pan¬demic, known as the Asian flu because it came from Hong Kong, and was relatively low in the 1968 pandemic. In 1976 there was a flu outbreak in Fort Dix, N.J., that in some cases was caused by the swine flu virus, believed by many experts to have caused the 1918 pandemic. Fearing another disaster, the United States and Canada set up a crash mass vaccina¬tion program. But when some people who had been vacci¬nated developed Guillain-Barre syndrome, a rare type of temporary paralysis, the U.S. program was canceled. A pandemic never developed.