Tracking the Philly Killer

Scientists find a lair for the Legionnaires' disease bug

Few ailments in the history of epidemic diseases have been more baffling than the one that struck more than 200 people during an American Legion convention in Philadelphia in 1976. Since then, disease detectives have isolated the bacterium-like organism that causes Legionnaires' disease. But if this dangerous form of pneumonia, which is now suspected of afflicting up to 45,000 people a year in the U.S. alone and requires treatment with the antibiotic erythromycin, is ever to be fully understood, researchers must know where the as yet unnamed infecting agent usually lives and how it is transmitted to humans.

Last week, after investigating a recent outbreak in Bloomington, Ind., which killed three people, Atlanta's Center for Disease Control announced a partial solution of that puzzle. The organism, or one closely resembling it, was found in water from an air conditioning cooling tower atop the Indiana University Memorial Union Hotel, where many of the victims had stayed, as well as in a nearby creek. The key to the discovery: two new culture media specifically designed to foster laboratory growth of the bug, which ordinarily multiplies so slowly that it is obscured by other bacteria.

CDC Epidemiologist David Fraser was unable to say how the microbe got into the water; one theory: it was carried there by particles of dust, possibly from nearby construction activity. But he did note encouragingly that when antirust materials or algicides are added to the contaminated water, the organism perishes.

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