Legionnaires' Disease

What is legionellosis?

Legionellosis is a bacterial disease of the lungs caused by Legionella pneumophila. The disease can range from a mild respiratory illness to severe pneumonia and death. The most common form of legionellosis is known as "Legionnaires' disease," named after an outbreak in 1976 when many people who attended an American Legion conference in Philadelphia became ill.

 How common is legionellosis?

It is estimated that between 8,000 and 18,000 people are hospitalized with 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.  The disease can occur at any time of the year, but is more common in the summer and early autumn. 

How are people infected with legionella?

Legionella bacteria are widely distributed, and normally grow best in warm water environments. They have been found in creeks and ponds, water taps (primarily hot water taps), hot water tanks, cooling towers and evaporative condensers, whirlpool spas, and decorative fountains.

Most people contract the disease by inhaling mist or vapor from a water source contaminated with the bacteria.  In some cases, the disease may be transmitted by other ways, such as aspirating contaminated water.  The disease is not contracted by drinking contaminated water, and person-to-person spread of legionellosis 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.

Because man-made water systems are the most likely source of Legionella, appropriate maintenance is very important.  Water temperatures can be raised to reduce transmission, and chemical treatments or biocides can be administered to water systems to inhibit growth of bacteria.

What are the usual symptoms of legionellosis?

The incubation period, the time between exposure and onset of illness, is two to ten days, but most often five to six days.
Legionellosis usually begins with symptoms like high fever (102 degrees F - 105 degrees F), chills, muscle pain, and headache.  Other symptoms may include cough (which may be dry or productive), shortness of breath, chest pain, or even gastrointestinal symptoms like diarrhea. Legionnaires' disease cannot be distinguished from other causes of pneumonia based on symptoms alone. Laboratory testing is required to establish this diagnosis.

Who is most at risk for legionellosis?

People of any age may get Legionnaires' disease, but the disease most often affects persons older than 50.  The disease is rare in people younger than 20 years of age.  People at high-risk of acquiring the disease include current and former smokers, persons with chronic lung disease like emphysema or COPD, or those with compromised immunity (like patients who receive corticosteroids or have had an organ transplant).  People with underlying illnesses, such as cancer, kidney disease, diabetes, or AIDS are also at higher risk.

How is legionellosis diagnosed?

A chest exam and/or x-ray is usually performed to confirm a diagnosis of pneumonia. The most common laboratory test is the urinary antigen test, which detects the presence of Legionella antigen in the urine.  A diagnosis of legionellosis can be confirmed by successful culture (isolation and growth) of the bacteria from specimens taken from an ill patient. 

 What is the treatment for legionellosis?

Hospitalization may be required for patients with legionellosis.  Most cases can be successfully treated with antibiotics.  There is no vaccine to prevent legionellosis.

How are cases of legionellosis reported?

Legionellosis is a reportable disease in the state of Illinois, and cases must be reported to the local health department within seven days.  Timely reporting allows identification of additional cases and control of possible contaminated sources.