What You Should Know About. Legionellosis is an illness caused by infection with the bacterium Legionella pneumophilia. Most cases of Legionnaires' disease occur as single isolated events.
Outbreaks are relatively rare.
An additional unknown number are infected with Legionella bacterium and have mild symptoms or no illness at all. In New Jersey approximately 40 cases of Legionellosis are reported each year. The disease most often affects middle-aged and older persons. Those who smoke cigarettes, drink heavily, have chronic lung disease, or lowered immune system resistance due to underlying disease or chemotherapy are at higher risk of becoming ill with Legionellosis. The disease is spread through the air from a soil or water source contaminated with Legionella bacteria, such as cooling towers and showers.