Legionellosis (Legionnaires' Disease, Pontiac Fever)

Legionellosis is an infectious disease generally caused by the bacteria Legionella pneumophila, which is responsible for approximately 90% of the infections. Legionellosis may take two forms. The more serious form, Legionnaires’ Disease can develop into pneumonia. The second form, Pontiac Fever produces a milder disease without pneumonia. It is difficult to distinguish Legionnaires’ Disease from other types of pneumonia by symptoms alone; laboratory tests are required for diagnosis.

Anyone can get Legionellosis, but people with weakened immune systems due to chronic diseases such as diabetes, kidney failure, HIV infection, or persons on medicines used to prevent organ rejection after organ transplantation are at highest risk for the disease. Persons who smoke or heavily consume alcohol are also more likely to get the disease. Cases of disease may occur throughout the year, but most cases occur in the summer and fall.

The time between the patient's exposure to the Legionella bacteria and the onset of illness for Legionnaires’ Disease is from two to ten days. For several days, the person may feel tired and weak. Most patients who are admitted to the hospital develop high fever often greater than 102°F. Cough can be the first sign of a lung infection. The cough may be sufficiently severe to cause patients to cough up mucous. Gastrointestinal symptoms are common with diarrhea being the most common symptom. Many patients have nausea, vomiting, and stomach discomfort. Other common symptoms include headaches, muscle aches, chest pain, and shortness of breath. Many antibiotics are highly effective against Legionella bacteria and should be prescribed by your health care provider.

For those who develop the Pontiac Fever form of Legionellosis, onset of illness is shorter, generally a few hours to 2 days. Cases may experience fever and muscle aches, but do not develop pneumonia. They generally recover in 2 to 5 days without treatment.

Person-to-person spread of Legionellosis does not occur. Legionella bacteria are natural inhabitants of water and can be detected in rivers, lakes, and streams, and some species have been recovered from soil. The organisms can survive in a wide range of conditions. People may become infected when they inhale aerosolized Legionella bacteria carried in the mist generated by such things as water-cooling towers, hot tubs, showerheads, vegetable misting devices, and decorative fountains.