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Legionnaire disease


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

Alternative Names

Legionella pneumonia; Pontiac fever; Legionellosis


The bacteria that cause Legionnaire 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 abuse
  • 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 tend to get worse during the first 4 to 6 days. They most often improve in another 4 to 5 days.

Symptoms may include:

  • Chest pain
  • Cough that does not produce much sputum or mucus (dry cough)
  • Coughing up blood
  • Diarrhea, nausea, vomiting, and abdominal pain
  • Fever, shaking chills
  • General discomfort, uneasiness, or ill feeling (malaise)
  • Headache
  • Joint pain
  • Loss of energy
  • Muscle aches and stiffness
  • Problems with balance
  • 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:


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

Outlook (Prognosis)

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

  • Have chronic diseases
  • Become infected while in the hospital
  • Are elderly

When to Contact a Medical Professional

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


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. 8th ed. Philadelphia, PA: Elsevier Saunders; 2015:chap 234.

Marrie TJ. Legionella infections. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 25th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 314.

Review Date:2/2/2015
Reviewed By:Denis Hadjiliadis, MD, MHS, Paul F. Harron Jr. Associate Professor of Medicine, Pulmonary, Allergy, and Critical Care, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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