The 1976 Legionnaires Disease outbreak also known as Legion Fever, refers to the first known cases of infection by Legionella pneumophila in the United States.
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 Legionaires, mostly men, attended the convention. The date and city were chosen to coincide with America’s celebration of the 200th anniversary of the signing of the US Declaration of Independence at Philadelphia in 1776.
On July 27, three days after the convention ended, Legionnaire Ray Brennan, a 61-year-old retired US Air Force captain and an American Legion bookkeeper, died at his home of an apparent heart attack. Brennan had returned home from the convention on the evening of July 24 complaining of feeling tired. On July 30, another Legionnaire, Frank Aveni, aged 60, also died of an apparent heart attack, as did three other Legionnaires. All of them had been convention attendees. Twenty-four hours later, on August 1, six more Legionnaires died. They ranged in age from 39 to 82, and, like Ray Brennan, Frank Aveni, and the three other Legionnaires, all had complained of tiredness, chest pains, lung congestion, and fever.
Three of the Legionnaires had been patients of Ernest Campbell, a physician in Bloomsburg, Pennsylvania, who noticed that all three men had been at the Legionnaires convention in Philadelphia. He contacted the Pennsylvania Department of Health. Officials at the American Legion also began getting notices of the sudden deaths of several members, all at the same time. Within a week, more than 130 people, mostly men, had been hospitalized, and 25 had died.
The U.S. Centers for Disease Control and Prevention mounted an unprecedented investigation and, by September, the focus had shifted from outside causes, such as a disease carrier, to the hotel environment itself. 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, which then spread it through the building. This finding prompted new regulations worldwide for climate control systems.
Complicating the situation was a fear among the public that the original cluster of 14 cases, six of whom died all within days of each other, represented an outbreak of swine flu. The total number of cases reached 211, and of those, 29 had died. At the time of the outbreak, epidemiological investigation protocols did not include active participation by both the laboratory specialists and investigators. No effective communication existed between scientists in the field interviewing patients, and those in the laboratory testing specimens.
While the Center for Disease Control responded rapidly, as did the Pennsylvania Health Department, it wasn't until nearly a year later that Joseph McDade made the discovery that a previously identified bacterium was the cause of the outbreak. It had not been considered previously because it was believed to affect only animals. The bacterium was later named Legionella pneumophila.