Legionnaires’ disease outbreak in Philadelphia in 1976 was mysterious and deadly – 50 years later, scientists know the cause but outbreaks continue

The source was a newly discovered bacterium called Legionella pneumophila that can thrive in household pipes, whirlpools, cooling units and outdoor fountains.

By: Charles N. Haas, Drexel University and Robert Promisloff, Drexel University, The Conversation

Outlets: The Conversation

Published: June 19, 2026

Words: 1,006

Last Updated: 1 month ago

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By Charles N. Haas, Drexel University and Robert Promisloff, Drexel University

Soon after Philadelphia hosted America’s bicentennial celebrations in late July 1976, more than 200 attendees of the American Legion Convention at the Bellevue-Stratford Hotel in Philadelphia fell ill with pneumonia symptoms, including fever, cough and trouble breathing.

Thirty-four of them died.

One of us was a newly minted pulmonary fellow at Hahnemann University Hospital. The hospital was just a mile from the …

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