Legionnaires' Disease

Written by Jacquelyn Cafasso | Published on July 9, 2012
Medically Reviewed by George Krucik, MD

What Is Legionnaires’ Disease?

Legionnaires’ disease is a serious type of lung infection, or pneumonia. It is caused by bacteria called Legionella. The bacteria and the disease were named following an outbreak of the infection at a Philadelphia convention of the American Legion in 1976.

The bacteria usually grow best in warm water. People get infected with Legionella by breathing in contaminated droplets of water in the air. Outbreaks have been linked to whirlpool spas in hotels and cruise ships and to water systems in hospital buildings.

According to the Centers for Disease Control and Prevention (CDC), 8,000 to 18,000 people are hospitalized in the United States each year for Legionnaires’ disease(CDC ).The number of infections, however, is probably higher, as many infections are not diagnosed or reported. The symptoms of Legionnaires’ are similar to those of other types pneumonia. They include fever, chills, and a cough.

Not everyone exposed to Legionella will become sick. If illness does occur, it can be very serious. The CDC states that Legionnaires’ disease can be fatal in 5 to 30 percent of cases(CDC ).

Legionella may also cause a more mild condition referred to as Pontiac fever. Pontiac fever does not cause pneumonia or death. It has symptoms similar to those of a mild flu and will usually go away on its own. Pontiac fever and Legionnaire’s disease are sometimes collectively called Legionellosis.

What Causes Legionnaires’ Disease?

Legionnaires’ disease is caused by an infection with bacteria called Legionella. The bacteria invade the lungs and lead to pneumonia.

Legionella usually live in warm freshwater. They are believed to be distributed worldwide. Common locations include:

  • hot tubs
  • whirlpool spas
  • swimming pools
  • cooling systems or air-conditioning units for large buildings, such as hospitals
  • showers
  • humidifiers
  • mist sprayers in grocery produce departments
  • fountains
  • natural bodies of water, such as lakes, rivers, streams, creeks, and hot springs

The bacteria survive outdoors, but are known to multiply rapidly in indoor water systems. People get infected by inhaling water droplets or mist in the air that is contaminated with the bacteria. The disease cannot be spread directly from person to person.

Who Is at Risk for Legionnaires’ Disease?

Not everyone who breathes in contaminated air droplets will get sick. The following people are at a higher risk of developing Legionnaires’ disease:

  • older adults (over age 65)
  • people in hospitals or nursing homes where diseases are spread more easily, especially after a surgery, intubation (having a tube placed in the trachea), or mechanical ventilation
  • smokers
  • people with a weakened immune system
  • people with lung disease
  • people whose job involves maintaining cooling or air conditioning systems
  • alcoholics

What Are the Symptoms of Legionnaires’ Disease?

Legionnaires’ disease will usually start causing symptoms two to 14 days after exposure to the bacteria. This period is called the incubation period. The symptoms are similar to those of other types of lung infections.

The most common symptoms include:

  • fever that may be above 104 °F
  • chills
  • cough, with or without mucus or blood

Other symptoms may include:

  • headaches
  • muscle aches
  • loss of appetite
  • chest pain
  • fatigue
  • general feeling of sickness

What Are the Complications of Legionnaires’ Disease?

If not treated, complications are similar to those of other types of severe pneumonia and can be life-threatening. These include:

  • respiratory failure
  • septic shock (an overwhelming infection that leads to very low blood pressure)
  • kidney and multi-organ failure

These complications can progress rapidly and lead to death. This is especially true if your immune system is already weakened.

How Is Legionnaires’ Disease Diagnosed?

Your doctor may test your urine for the presence of Legionellaantigens. Antigens are substances that your body recognizes as harmful. Your body produces an immune response to antigens. The doctor may also test your blood or a sample of sputum for the Legionellabacteria.

Your doctor may also perform a chest X-ray. An X-ray is used to determine the extent of your pneumonia. It will not be used to confirm Legionnaires’ disease.

How Is Legionnaires’ Disease Treated?

The disease is always treated with antibiotics. Treatment is usually started as soon as Legionnaires’ disease is suspected, without waiting for confirmation.

Elderly people and people with other health conditions will typically be admitted to the hospital. These people are particularly vulnerable to the effects of Legionnaires’ disease. They may receive oxygen or other breathing support. They may also be given fluids and electrolytes directly into a vein in their arm to prevent dehydration.

What Is the Outlook After Treatment?

The outlook is typically good in otherwise healthy people who receive prompt treatment. The death rate depends on the severity of the disease and how quickly treatment is received. Faster treatment means better results. The disease is usually most serious in those with a weakened immune system or another disease.

How Can Legionnaires’ Disease be Prevented?

There is no vaccine available for Legionnaires’. It is possible to help prevent the disease by properly disinfecting and cleaning potential sources of the bacteria. Preventative measures include:

  • disinfecting and cleaning cooling towers
  • regular draining and cleaning pools and hot tubs
  • using chemical treatments, such as chlorine, in pools and spas
  • keeping hot water systems at above 140 degrees °F and cold water systems below 68 degrees °F

Finally, avoiding smoking can significantly lower your risk of getting Legionnaires’ disease.

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