25 Years Ago In TIME

By Harriet Barovick, Ellin Martens and Sora Song

American Legion conventioneers in Philadelphia were dying of a mysterious illness. Eventually, DISEASE DETECTIVES would discover the cause to be a bacterium spread through air-conditioning systems, but until then, near panic took hold:

There was an invisible, impersonal mass killer on the loose. The knowledge rekindled, despite all the advances of modern medicine, humanity's ancient memories of epidemics beyond understanding or control. Even as the first waves of shock and fear began to spread, the search for the killer began in one of the most intensive efforts at medical sleuthing ever undertaken in the U.S. Now that the alert had been sounded, the case files quickly swelled. Within the week, more than 130 people, mostly men, had been stricken and hospitalized, and 25 had died. Each report fueled the nation's anxiety, producing panicky calls to doctors and hospitals from people who developed any of the reported and not uncommon symptoms... "There's an outside chance we may never find out the cause," says CDC director David Spencer. "I think we will. But there are times when disease baffles us all. It may be sporadic, a one-time appearance." Whatever the solution--or lack of one--to the mystery of the Philadelphia killer, the outbreak served as a jarring reminder that all the marvels of modern technology have not yet made the U.S. immune to a sudden pestilence.

--TIME, Aug. 16, 1976