Legionnaire disease is an infection of the lungs and airways caused by Legionella bacteria.
Legionella pneumonia; Pontiac fever
Causes, incidence, and risk factors
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-age or older people. In rare cases, children can get the infection. When they do, the disease is less severe.
Risk factors include:
Weakened immune system, such as during cancer treatment or taking steroid medicines
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 medications
Symptoms tend to get worse during the first 4 - 6 days. They most often improve in another 4 - 5 days.
Symptoms may include:
Cough that does not produce much sputum or mucus (dry cough)
Coughing up blood
Diarrhea, nausea, vomiting, and abdominal pain
General discomfort, uneasiness, or ill feeling (malaise
Loss of energy
Muscle aches and stiffness
Problems with balance
Shortness of breath
Signs 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 and oxygen, which is given through a mask or breathing machine.
Legionnaire disease can be life-threatening. The risk of dying is higher in patients who:
- Have chronic diseases
- Become infected while in the hospital
Calling your health care provider
Make an appointment with your health care provider if you have any type of breathing problem.
Edelstein PH, Ciancioti NP. Legionella. In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, PA: Elsevier Churchill-Livingstone; 2009:chap 232.
Torres A. Menendez R, Wunderink R. Pyrogenic bacterial pneumonia and lung abscess. In: Mason RJ, Broaddus VC, Martin TR, et al., eds. Murray & Nadel's Textbook of Respiratory Medicine. 5th ed. Philadelphia, PA: Elsevier Saunders; 2010:chap 32.
Denis Hadjiliadis, MD, Assistant Professor of Medicine, Division of Pulmonary, Allergy and Critical Care, University of Pennsylvania, Philadelphia, PA. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, David R. Eltz, Stephanie Slon, and Nissi Wang.