In 1977, the U.S. Centers for Disease Control and Prevention (CDC) isolated Legionella pneumophila, which caused a deadly outbreak of Legionnaires’ disease in a Philadelphia hotel. Legionella was discovered after an outbreak in 1976 among people who went to a Philadelphia convention of the American Legion. Those who were affected suffered from a type of pneumonia (lung infection) that eventually became known as Legionnaires’ disease.