What is legionellosis?

Legionellosis is a bacterial disease caused by Legionella pneumophilia. The disease, which may occur in outbreaks or as single cases, can cause mild respiratory illness or pneumonia. The most common form of the disease is known as "Legionnaires' disease."

How common is legionellosis?

It is estimated that about 8,000 to 18,000 people develop legionellosis in the United States each year. An additional unknown number are infected with the Legionella bacterium but have mild symptoms or no illness at all.

In Illinois, between 25 and 50 cases are reported each year.

Why is it called legionellosis?

An outbreak of this disease occurred in Philadelphia in 1976, largely among people attending an American Legion convention; this led to the name "Legionnaires' disease." Subsequently, the bacterium causing the illness was named Legionella and the name of the illness was changed to legionellosis.

Is this a new disease?

No. While the bacterium was only identified following the 1976 convention, earlier cases have been confirmed as far back as 1947 and cases probably occurred before that date.

Where are Legionella found?

Legionella are widely distributed in our environment. They have been found in creeks and ponds, hot and cold water taps (primarily hot water taps), hot water tanks, water in cooling towers and evaporative condensers, and whirlpool spas.

Most people contract the disease by inhaling mist from a water source contaminated with the bacteria. In some cases, the disease may be transmitted by other ways, such as aspirating contaminated water. All studies to date have shown that person-to-person spread does not occur. Outbreaks occur following the exposure of many individuals to a common source of the bacteria in the environment. When a single case occurs, it is extremely difficult to pinpoint a source. Environmental testing is recommended only when multiple cases have the same potential exposure.

How severe is the illness?

Legionellosis can be a mild respiratory illness or it can be severe enough to cause death. Studies have shown that about 5 percent to 30 percent of known cases have been fatal. From 1 percent to 20 percent of healthy adults have antibodies showing previous exposure to the organism, but only a small percentage have a history of previous pneumonia. This suggests that many cases of Legionnaires' disease go undiagnosed.

Who gets legionellosis?

People of any age may get Legionnaires' disease, but the disease most often affects middle-aged and older persons, particularly those who smoke heavily. People with underlying illness, such as cancer, kidney disease, diabetes, AIDS, chronic lung disease or heart failure, or who have had an organ transplant also are at higher risk. Individuals who take corticosteroids (e.g., prednisone, azathioprine or cyclosporine) are also at higher risk.

What are the usual symptoms of legionellosis?

The most common symptoms of legionellosis are fever (102 degrees F - 105 degrees F), chills, and a cough (which may be dry or productive). Some patients also have muscle aches, headaches, tiredness, loss of appetite and, occasionally, diarrhea.Chest X-rays usually confirm pneumonia. Legionnaires' disease cannot be distinguished from other causes of pneumonia based on symptoms alone. Special testing is required to establish this diagnosis.

How soon do symptoms occur?

The period between exposure and onset of illness for Legionnaires' disease is two to 10 days, but most often five to six days.

How is legionellosis diagnosed?

Legionellosis usually is diagnosed by one of four methods. The organism can be seen under a microscope in sputum or tissue using special stains. The bacteria also may be cultured from sputum or tissue; this usually takes two to five days. Passing a small lighted tube into the lungs (a procedure called bronchoscopy) or sometimes even an operation may be required to obtain a specimen for staining or culturing. The bacteria also can be detected in the urine. Comparison of blood tests obtained during the illness and several weeks later may be needed to make the diagnosis when other methods are inconclusive or are negative.

What is the treatment for legionellosis?

Antibiotics appear to be effective in treating the disease; erythromycin is currently recommended as the drug of choice. Other drugs are available for patients unable to tolerate erythromycin.

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Illinois Department of Public Health
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Springfield, Illinois 62761
Phone 217-782-4977
Fax 217-782-3987
TTY 800-547-0466
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