Type of pneumonia , first identified in American Legion conventioneers in 1976, 29 of whom died.
The cause was identified as a previously unknown bacterium, Legionella pneumophila , later revealed as causing earlier mysterious outbreaks at widely separated places. Usually, malaise and headache are followed by high fever and often chills, dry cough, shortness of breath, and pain, occasionally with mental confusion. Contaminated water (e.g., in water-distribution systems, humidifiers, and whirlpool spas) is usually suspected as the source. The disease is treated with antibiotics.