Legionella Pneumophila Pneumonia - Legionnaires' Disease

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 Legionella pneumophila bacteria enter the lungs when the person inhales contaminated water. The bacteria grow in the lungs and cause pneumonia, or lung infection. The bacteria can also cause extrapulmonary infections, or 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 Legionella pneumophila bacteria. 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 infection are as follows:

Legionnaires' disease was first identified in the United States. It has been detected in several other countries. Scientists believe it occurs everywhere in the world. Following is a list of people who are at higher risk for this infection:

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. It is less common in the arid West.

What are the signs and symptoms of the infection?

Symptoms of Legionnaires' disease begin after an incubation period of 2 to 10 days. Common symptoms include the following:

Following are some of the less common symptoms:

Legionella pneumophila infections can cause symptoms in other parts of the body, including the heart. Symptoms are specific to the body part that is infected.

How is the infection diagnosed?

Diagnosis begins with a medical history and physical exam. The healthcare provider may order tests, including the following:

A bronchoscopy may be done to obtain samples of lung tissue for examination. A flexible scope is inserted through the windpipe into the lungs.

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. Following are some of the methods used to reduce levels of Legionella pneumophila in water supplies:

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. Vaccinations are being developed for use in high risk individuals.

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, or pus pockets. These effects are usually not severe.

What are the risks to others?

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

What are the treatments for the infection?

Legionnaires' disease is treated with antibiotics, such as erythromycin. A stronger medication, rifampin, may be used in severe cases.

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.

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 provider until he or she is completely recovered. Any new or worsening symptoms should be reported to the provider.

Author:Thomas Fisher, MD
Date Written:
Editor:Ballenberg, Sally, BS
Edit Date:05/31/01
Reviewer:Eileen McLaughlin, RN, BSN
Date Reviewed:09/24/01