Legionellosis is a bacterial disease which may cause life-threatening pneumonia. Fewer than 150 cases are reported each year in the Commonwealth. Most cases occur as single isolated events all year long.
Outbreaks are relatively rare, but occur most often in the summer.
Subsequently, the bacterium causing the illness was identified and named Legionella pneumophila , and the name of the disease was changed to legionellosis. It is estimated that about 25,000 people in the United States develop legionellosis each year. An additional unknown number are infected with legionella bacteria and have either mild symptoms, or no illness at all. Legionellosis can be a mild respiratory illness, or severe enough to cause death. Legionella bacteria are widely distributed in the environment.