1976 Philadelphia Legionnaires' disease outbreak

The 1976 Legionnaires' disease outbreak, occurring in the late summer in Philadelphia, Pennsylvania, United States at an annual American Legion convention, 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.

[3] On July 27, three days after the convention ended, Legionnaire Ray Brennan, a 61-year-old retired US Air Force captain employed as a Legion bookkeeper, died at his home of an apparent heart attack.

[3] Three of the Legionnaires had been patients of Dr. Ernest Campbell, a physician in Bloomsburg, Pennsylvania, who noticed that the only common link between the three was that they had attended the convention.

In January 1977, the Legionella bacterium was finally identified and isolated and was found to be breeding in the cooling tower of the hotel's air conditioning system,[5] which then spread it through the building.

[8] Complicating the situation was a fear among the public that the original cluster of 14 cases, six of whom died within a few days of each other, represented an outbreak of swine flu.

[10] While the Center for Disease Control (as it was called in that era) 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 patients failed to grow bacteria when incubated in culture medium.