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Legionnaires Disease

Legionnaires Disease

Alternate Names

  • pneumonia


Legionnaire's disease is a mild to severe pneumonia. It is caused by the bacteria Legionella pneumophila. Legionnaires' disease occurs when people are exposed to water contaminated with the bacteria.

What is going on in the body?

The bacteria enter the lungs when the person inhales contaminated water. The bacteria grow in the lungs, causing pneumonia, and can also cause extrapulmonary infections, that is, infections outside the lung.
Extrapulmonary infections occur when the bacteria spread through the bloodstream or lymph system. The most common site of infection outside of the lungs is the heart.


What are the causes and risks of the infection?

Legionnaires' disease is caused by the bacteria Legionella pneumophila. The bacteria are found in many kinds of water supplies. The bacteria grow rapidly in water that is warm and still.
Some of the most common sources of Legionella infection are as follows:
  • air conditioning systems
  • hot tubs, whirlpools, and spas
  • hot water tanks
  • institutional water supplies
  • showers
Though Legionnaires' disease was first identified in the United States, it has been detected in several other countries and scientists believe it occurs everywhere in the world.
Those at higher risk for this infection include:
  • individuals with chronic disease, such as diabetes
  • individuals with weakened or damaged immune systems
  • people who are middle-aged or older
  • people with chronic lung disease, such as chronic obstructive pulmonary disease
  • those on chemotherapy
  • those receiving dialysis, or blood filtering for kidney disease
  • those who smoke cigarettes
The infection can occur at any time, but it is most common in the summer and early fall. It is more common in humid areas of the U.S., and less common in the arid West.


What can be done to prevent the infection?

Complete sterilization of the bacteria from water supplies is not practical. When a contaminated water source is identified, it may be treated.
Some of the methods used to reduce levels of the bacteria in water supplies include:
  • exposure to ultraviolet light
  • flushing
  • superheating the water
People with compromised immune systems are at high risk for Legionnaires' disease. Facilities that care for these people should monitor water supplies for the bacteria.
Research toward possible legionella vaccines has been reported over a period of several years, but little progress has been made.


How is the infection diagnosed?

Diagnosis begins with a medical history and physical exam. The healthcare professional may order tests, including:
  • antibody titer tests
  • a chest X-ray
  • examination of the person's sputum for bacteria
  • urine tests
A bronchoscopy may be done to obtain samples of lung tissue for examination. In this procedure, a flexible, lighted scope is inserted through the windpipe into the lungs.

Long Term Effects

What are the long-term effects of the infection?

As many as 5% to 30% of the people with Legionnaires' disease die from the infection. Long-term effects include lung scarring and abscesses (pus pockets). These effects are usually not severe.

Other Risks

What are the risks to others?

Legionnaires' disease is not communicable from one person to another. It is acquired only by exposure to contaminated water.


What are the treatments for the infection?

Legionnaires' disease is treated with antibiotics, such as azithromycin (i.e., Zithromax, Zmax), clarithromycin (i.e., Biaxin), levofloxacin (i.e., Levaquin), ciprofloxacin (i.e., Cipro, Proquin), erythromycin, doxycyline (i.e., Adoxa, Doryx, Oracea, Periostat, Vibramycin), minocycline (i.e., Minocin, Solodyn), trimethoprim/sulfamethoxazole (i.e., Bactrim, Septra) or rifampin.

Side Effects

What are the side effects of the treatments?

Antibiotics may cause stomach upset, rash, and allergic reactions. Rifampin turns the person's urine and other body secretions an orange color.

After Treatment

What happens after treatment for the infection?

Legionnaires' disease can be persistent. It can last for several weeks to several months, if not treated. After treatment, individuals should be aware that relapses can occur.


How is the infection monitored?

The individual may have regular visits with the healthcare professional until he or she has completely recovered. Any new or worsening symptoms should be reported.

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