1976 Philadelphia Legionnaires' disease outbreak 1976 Philadelphia Legionnaires' disease outbreak The 1976 Legionnaires disease outbreak, occurring in the late summer in Philadelphia, Pennsylvania, was the first occasion in which a cluster of a particular type of pneumonia cases were determined to be caused by the "Legionella pneumophila" bacteria. Previous outbreaks were retroactively diagnosed as being most probably caused by Legionella bacteria. On July 21, 1976, the American Legion opened its annual three-day convention at the Bellevue-Stratford Hotel in Philadelphia, Pennsylvania. More than 2,000 Legionnaires, mostly men, attended the convention. The date and city were chosen to coincide with America’s celebration of the 200th anniversary of
1976 Philadelphia Legionnaires' disease outbreak testing specimens. While the Center for Disease Control responded rapidly, as did the Pennsylvania Health Department, it took six months for the CDC microbiologist Joseph McDade to discover the cause of the outbreak. He initially thought the cause was viral because blood and tissues from the victims failed to grow bacteria when incubated in culture medium. His subsequent attempts to isolate the viral agent in eggs included antibiotics to kill off "contaminating" bacteria. It was only when he omitted the antibiotics that the bacteria grew in eggs. Attempts to reproduce the disease in mice, the standard laboratory animal model, also