Legionellosis

 

• Legionellosis [lee-juh-nel-OH-sis] is caused by bacteria found in water sources in the environment.
• People get legionellosis when they inhale water mist containing the bacteria. Infections have been traced to mist-producing devices, such as certain air-conditioning systems.
• Legionellosis has two forms: Pontiac fever, a mild respiratory infection, and Legionnaires' disease, a serious and potentially fatal form of pneumonia.
• Pontiac fever requires no treatment. Legionnaires' disease is treatable with antibiotics.
• Outbreaks can usually be controlled by identifying and cleaning contaminated water sources.

 

What is legionellosis?

Legionellosis is a lung infection that can be mild or severe enough to cause death. In its mild form, it is called Pontiac fever. The more severe form of infection, a type of pneumonia, is called Legionnaires' disease. Legionnaires' disease got its name in 1976 when an outbreak of pneumonia occurred in people attending an American Legion convention in Philadelphia.

 

What is the infectious agent that causes legionellosis?

Legionellosis is caused by Legionella pneumophilia, a bacterium.

 

Where is legionellosis found?

Cases of legionellosis have been identified throughout the United States and in several other countries. The disease likely occurs worldwide.

Legionella bacteria are widespread in natural, industrial, and recreational water sources in the environment. The bacteria live best in warm, stagnant water. They have been found in creeks and ponds, hot and cold water taps, hot water tanks, and water in cooling towers and condensers of large air-conditioning systems.

 

How do people get legionellosis?

People get legionellosis when they inhale aerosols (water mist) that carry Legionella bacteria. People can be exposed to aerosols from mist-producing devices (especially water heaters and air-conditioning systems) in their homes and in workplaces, hospitals, or other public places.

Because Legionella bacteria live in the environment, groups of persons who are exposed to a common source of water mist can be exposed to the bacteria at the same time. When this happens, a legionellosis "outbreak" occurs among some members of the group. Legionellosis outbreaks have been traced to whirlpools, showers, room humidifiers, decorative spraying fountains, and large air-conditioning cooling towers.

For most cases not associated with outbreaks, the water source responsible for infection is not known. Legionellosis is not spread from infected persons to uninfected persons.

 

What are the signs and symptoms of legionellosis?

Persons with Pontiac fever have fever and muscle aches but do not have pneumonia. They usually get better in 2 to 5 days without treatment.

Persons with Legionnaires' disease are generally much sicker. They usually have fever, chills, and a cough, which might be dry or might produce sputum. Some persons also have muscle aches, headache, tiredness, loss of appetite, and, occasionally, diarrhea. Temperatures often reach 102^oF-105^o F, and chest x-rays often show signs of pneumonia.

 

How soon after exposure do symptoms appear?

The time between exposure and the beginning of symptoms for Legionnaires' disease is 2 to 10 days. For Pontiac fever, it is shorter, usually a few hours to 2 days.

 

How is legionellosis diagnosed?

It is difficult to distinguish Legionnaires' disease from other types of pneumonia by symptoms alone; special tests are needed for a diagnosis. Because these tests are not routinely performed on persons with fever or pneumonia, a health-care provider must consider the possibility of legionellosis to ask for the appropriate tests.

Several types of tests are available. These include: detecting Legionella bacteria in sputum, finding evidence of Legionella in body fluids, or finding Legionella antibodies in the blood after illness begins.

 

Who is at risk for legionellosis?

Anyone can get legionellosis, but the illness most often strikes middle-aged and older persons, especially those who smoke cigarettes or have chronic lung disease. Persons whose immune systems are weakened by cancer, kidney failure requiring dialysis, diabetes, or HIV infection are also at high risk.

 

What complications can result from legionellosis?

The main complication is respiratory failure requiring use of a respirator. Multiple organ failure and shock can lead to death. The overall death rate for those with legionellosis who develop pneumonia is about 15%. The rate is higher for persons with underlying diseases.

 

What is the treatment for legionellosis?

Pontiac fever requires no specific treatment.

Legionnaires' disease is treated with antibiotics. Treatment is started as soon as Legionnaires' disease is suspected, without waiting for test results. Erythromycin or a related antibiotic are the drugs of choice. In severe cases, a second drug, rifampin, can be added.

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How common is legionellosis?

An estimated 15,000 to 30,000 persons get Legionnaires' disease in the United States each year. An additional unknown number are infected with Legionella, have no symptoms or only a mild illness, and are never diagnosed and reported.

Cases occur singly and in outbreaks. Although outbreaks of Legionnaires' disease receive more attention, legionellosis most often occurs as a single, isolated case. Outbreaks occur most often in the summer and early fall, but cases occur year-round.

 

Is legionellosis a new or emerging infectious disease?

Legionellosis is not a new disease. Although the Legionella bacterium was identified only recently, cases from as far back as 1947 have been confirmed. Reported cases are increasing as health-care providers become more familiar with the disease and diagnostic tests become more widely available.

 

How can legionellosis be prevented?

Individual cases of legionellosis are not preventable. However, they are often investigated to confirm the diagnosis and rule out an outbreak.

If an outbreak occurs, public health experts conduct an investigation to look for a possible source and to recommend prevention and control measures, such as decontamination of the aerosol-producing device. Long-term prevention efforts center on improving the design and maintenance of cooling towers and plumbing systems to limit the growth and spread of Legionella bacteria.

 

Where can I find more information about legionellosis?

http://www.cdc.gov/ncidod/diseases/legion/legion.htm

 

This fact sheet is for information only and is not meant to be used for self-diagnosis or as a substitute for consultation with a health-care provider. If you have any questions about the disease described above, consult a health-care provider.