Legionnaires' disease is a severe bacterial infection of the respiratory tract, caused by Legionella pneumophila. This microorganism may also affect other body systems. Afflicted patients may have pulmonary, gastrointestinal tract, and central nervous system complications. Renal insufficiency may occur occasionally and can be severe enough to require dialysis.
Legionella bacteria were first identified as a cause of pneumonia in 1976, following an outbreak of pneumonia among people who had attended an American Legion convention in Philadelphia, Pennsylvania.

Causes

The major environmental source of the infection is water from reservoirs and cooling units of air conditioning systems. Lakes, creeks, and areas of excavation also may harbor the bacteria. Transmission is by breathing in droplets of contaminated water. Person-to-person transmission has not been documented. Those at risk are cigarette smokers, those with chronic lung disease, and persons receiving drugs that suppress the immune system.

Symptoms

Legionnaires' disease develops 2-10 days after exposure to the bacteria. The symptoms are similar to those of many other respiratory diseases, making it difficult to differentiate and diagnose.

Early symptoms include lethargy, headaches, fever, chills, muscle aches, and a lack of appetite. Respiratory symptoms such as coughing or congestion are usually absent. As the disease progresses, a dry, hacking cough develops and may become productive after a few days. In about a third of Legionnaires' disease cases, blood is present in the sputum. Half of the people who develop Legionnaires' disease suffer shortness of breath and a third complain of breathing-related chest pain.

Treatment