Legionnaires’ disease

Other Names

Legionellosis; Legionnaires disease

Legionnaires’ disease is a severe type of pneumonia caused by the bacteria Legionella. It is named Legionnaires’ disease because it was first discovered after a pneumonia outbreak among people who attended an American Legion Convention in Philadelphia, Pennsylvania in 1976.

Cause

The species Legionella pneumophila causes most cases, but other species of Legionella can also cause the disease. A person can become infected from Legionella when they inhale mist or water droplets that contain the bacteria. Sources of exposure may include showers, faucets, whirlpools, grocery store misters, and water droplets passing through ventilation systems in large buildings (such as hotels, office buildings, and hospitals).

Risk factors

Most healthy people exposed to Legionella do not get sick. People at increased risk of getting sick are:

• People 50 years or older
• Current or former smokers
• People with a chronic lung disease (like chronic obstructive pulmonary disease or emphysema)
• People with weak immune systems or who take drugs that weaken the immune system (like after a transplant operation or chemotherapy)
• People with cancer
• People with underlying illnesses such as diabetes, kidney failure, or liver failure

Various stages of the disease: Chest radiograph (A) and high-resolution computed tomography (B) at hospital admission, repeat high-resolution computerized tomography of the chest a week after hospital admission (C, D), shown in a 42-year-old male with severe pneumonia caused by L. pneumophila serogroup 11a

Transmission

After Legionella grows and multiplies in a building water system, water containing Legionella then has to spread in droplets small enough for people to breathe in. People can get Legionnaires’ disease or Pontiac fever when they breathe in small droplets of water in the air that contain the bacteria. Less commonly, people can get sick by aspiration of drinking water containing Legionella. This happens when water accidently goes into the lungs while drinking. People at increased risk of aspiration include those with swallowing difficulties.

Signs and Symptoms

People who get sick after being exposed to Legionella can develop two different illnesses: Legionnaires’ disease and Pontiac fever.

Legionnaires’ Disease Legionnaires’ disease is very similar to other types of pneumonia (lung infection), with symptoms that include:

• Cough
• Shortness of breath
• Fever
• Muscle aches
• Headaches

Legionnaires’ disease can also be associated with other symptoms such as diarrhea, nausea, and confusion. Symptoms usually begin 2 to 10 days after being exposed to the bacteria, but it can take longer so people should watch for symptoms for about 2 weeks after exposure. If you develop pneumonia symptoms, see a doctor right away. Be sure to mention if you may have been exposed to Legionella, have used a hot tub, spent any nights away from home, or stayed in a hospital in the last two weeks.

Pontiac Fever Pontiac fever symptoms are primarily fever and muscle aches; it is a milder infection than Legionnaires’ disease. Symptoms begin between a few hours to 3 days after being exposed to the bacteria and usually last less than a week. Pontiac fever is different from Legionnaires’ disease because someone with Pontiac fever does not have pneumonia.

Diagnosis

Legionellosis can present as two types of illness: Legionnaires’ disease and Pontiac fever. The two illnesses can be diagnosed with similar tests, but are treated differently.

Legionnaires’ Disease Diagnosis People with Legionnaires’ disease have pneumonia (lung infection), which can be confirmed by chest x-ray. Clinicians typically use two preferred types of tests to see if a patient’s pneumonia is caused by Legionella: Urine test Laboratory test that involves taking a sample of sputum (phlegm) or washing from the lung.

Pontiac Fever Diagnosis Clinicians can use a urine or blood test to see if someone has Pontiac fever. However, a negative test doesn’t rule out that someone may have it (this is called a false negative). Clinicians most often diagnose Pontiac fever when there are other known laboratory-confirmed legionellosis cases (either Legionnaires’ disease or Pontiac fever) who may have been exposed to Legionella at the same time or place.

Treatment

• Legionnaires’ disease requires treatment with antibiotics (medicines that kill bacteria in the body), and most cases of this illness can be treated successfully.
• Healthy people usually get better after being sick with Legionnaires’ disease, but they often need care in the hospital.
• Pontiac fever goes away without specific treatment.

Prevention

Water Management Programs There are no vaccines that can prevent Legionnaires’ disease. Instead, the key to preventing Legionnaires’ disease is to make sure that building owners and managers maintain building water systems in order to reduce the risk of Legionella growth and spread. Examples of building water systems that might grow and spread Legionella include:

• Hot tubs
• Hot water tanks and heaters
• Large plumbing systems
• Cooling towers (structures that contain water and a fan as part of centralized air cooling systems for building or industrial processes)
• Decorative fountains.

NIH genetic and rare disease info

• NIH info on Legionnaires’ disease

Legionnaires’ disease is a rare disease.

Legionnaires’ disease Resources
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