Home > Encyclopedia of Science > Legionnaires' Disease

• A mysterious outbreak
• Words to Know
• "Philly Killer"
• Discovery by CDC
• Course of disease
• Source of infection
• Attacks the susceptible
• A new "old" disease

Legionnaires' disease is an acute respiratory infection caused by a common bacteria that results in a serious case of pneumonia. It first became a well-known disease in 1976 when a serious outbreak occurred among a large number of people attending an American Legion convention. Researchers eventually discovered that the bacteria can be easily found in nature wherever there is warm and moist stagnant water, and that it is transmitted by breathing it in.