Legionnaires' disease

Legionnaires' disease is an infection primarily presenting as pneumonia caused by Legionella bacteria (legionellosis), also known as Legionnaires' disease. The pathogenic bacteria mainly originate from contaminated water sources and enter through the respiratory tract. Additionally, the pathogenic bacteria may also cause another clinical form characterized by fever, headache, and myalgia, which is milder in severity and is called Pontiac fever. In 1976, at a convention of the American Legion veterans in Pennsylvania held in a hotel in Philadelphia, among approximately 4,400 delegates and their families, 221 people successively developed pneumonia, with 34 deaths. Legionnaires' disease was thus named. Six months later, the pathogen was isolated and identified as a previously unclassified bacterium, which was named Legionella pneumophila. Subsequent retrospective studies found that Legionnaires' disease had already occurred in epidemics as early as 1957, and the pathogenic bacterium had been isolated as early as 1943.