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Diseases reference index «Legionnaire's disease»

Legionnaire's disease is an acute respiratory infection caused by Legionella bacteria.


The bacteria that cause Legionnaire's 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 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, although they have been reported in children. Typically, the disease is less severe in children.

Risk factors include:

  • Alcoholism
  • Cigarette smoking
  • Diseases such as kidney failure or diabetes
  • Diseases that weaken the immune system, including cancer
  • Long-term (chronic) lung disease, such as chronic obstructive pulmonary disease (COPD)
  • Long-term use of a breathing machine (ventilator)
  • Medicines that suppress the immune system, including chemotherapy and steroid medications
  • Older age


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

Symptoms may include:

  • Chest pain
  • Coughing up blood
  • Fever
  • Gastrointestinal symptoms, such as diarrhea, nausea, vomiting, and abdominal pain
  • General discomfort, uneasiness, or ill feeling (malaise)
  • Headache
  • Joint pain
  • Lack of coordination (ataxia)
  • Loss of energy
  • Muscle aches and stiffness
  • Nonproductive cough
  • Shaking chills
  • Shortness of breath

Exams and Tests

The health care provider will perform a physical exam, and may hear abnormal sounds called crackles when listening to the chest with a stethoscope.

Tests that may be done include:

  • Arterial blood gases
  • Chest x-ray
  • Complete blood count (CBC), including white blood cell count
  • Erythrocyte sedimentation rate
  • Liver function tests
  • Sputum culture for the Legionella bacteria
  • Sputum indirect fluorescent antibody test for the Legionella bacteria
  • Urine tests to check for Legionella pneumophila bacteria


Antibiotics are used to fight the infection. Treatment is started as soon as Legionnaire's disease is suspected, without waiting for confirmation by lab test.

Antibiotics commonly used to treat this condition include:

  • Quinolones (ciprofloxacin, levofloxacin, moxifloxacin, or gatifloxacin)
  • Macrolides (azithromycin, clarithromycin, or erythromycin)

Other treatments may include:

  • Fluid and electrolyte replacement
  • Oxygen (given through a mask or breathing machine)

Outlook (Prognosis)

Legionnaire's disease can be life-threatening. The death rate is higher in patients with other diseases. The death rate for patients who develop Legionnaire's disease while in the hospital is close to 50%, especially when antibiotics are started late.

Possible Complications

  • Lung failure
  • Death

When to Contact a Medical Professional

Make an appointment with your health care provider if you have any type of breathing problem.


Treating water delivery systems can prevent the spread of disease.

Alternative Names

Legionella pneumonia; Pontiac fever

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