Health Encyclopedia

Legionnaires disease

Definition

Legionnaires disease is an infection of the lungs and airways. It is caused by Legionella bacteria.

Alternative Names

Legionella pneumonia; Pontiac fever; Legionellosis; Legionella pneumophila; Legionnaires' disease

Causes

The bacteria that cause Legionnaires disease have been found in water delivery systems. They can survive in the warm, moist air conditioning systems of large buildings, including hospitals.

Most cases are caused by the bacteria Legionella pneumophila. The rest of the cases are caused by other Legionella species.

Spread of the bacteria from person to person has not been proven.

Most infections occur in middle-aged or older people. In rare cases, children can get the infection. When they do, the disease is less severe.

Risk factors include:

Alcohol use
Cigarette smoking
Chronic illnesses, such as kidney failure or diabetes
Long-term (chronic) lung disease, such as COPD
Long-term use of a breathing machine (ventilator)
Medicines that suppress the immune system, including chemotherapy and steroid drugs
Older age

Symptoms

Symptoms tend to get worse during the first 4 to 6 days. They most often improve in another 4 to 5 days.

Symptoms may include:

General discomfort, loss of energy, or ill feeling (malaise)
Headache
Fever, shaking chills
Joint pain, muscle aches and stiffness
Chest pain
Cough that does not produce much sputum or mucus (dry cough)
Coughing up blood (rare)
Diarrhea, nausea, vomiting, and abdominal pain
Shortness of breath

Exams and Tests

The health care provider will perform a physical exam. Abnormal sounds, called crackles, may be heard when listening to the chest with a stethoscope.

Tests that may be done include:

Arterial blood gases
Blood cultures or other tests to identify the bacteria
Bronchoscopy to view the airways and diagnose lung disease
Chest x-ray or CT scan
Complete blood count (CBC), including white blood cell count
Liver blood tests
Tests and cultures on sputum to identify Legionella bacteria
Urine tests to check for Legionella pneumophila bacteria
Molecular tests with polymerase chain reaction (PCR)

Treatment

Antibiotics are used to fight the infection. Treatment is started as soon as Legionnaire disease is suspected, without waiting for results of any lab test.

Other treatments may include receiving:

Fluids through a vein (IV)
Oxygen, which is given through a mask or breathing machine
Medicines that are breathed in to ease breathing

Outlook (Prognosis)

Legionnaires disease can be life threatening. The risk of dying is higher in people who:

Have long-term (chronic) diseases or compromised immune systems
Become infected while in the hospital
Are older adults

When to Contact a Medical Professional

Contact your provider right away if you have any type of breathing problem and think you have symptoms of Legionnaires disease.

References

Edelstein PH, Roy CR. Legionnaires' disease and Pontiac fever. In: Bennett JE, Dolin R, Blaser MJ, eds. Mandell, Douglas, and Bennett's Principles and Practice of Infectious Diseases. 9th ed. Philadelphia, PA: Elsevier; 2020:chap 232.

Marrie TJ. Legionella infections. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 298.

Review Date:1/22/2023
Reviewed By:Denis Hadjiliadis, MD, MHS, Paul F. Harron, Jr. Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team. Editorial update 01/19/2024.

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