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

Legionella pneumonia; Pontiac fever

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:

• Alcohol abuse 
• Cigarette smoking
• Chronic illnesses such as kidney failure or diabetes
• 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
• Older age

Symptoms tend to get worse during the first 4 - 6 days. They most often improve in another 4 - 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
• General discomfort, uneasiness, or ill feeling (malaise)
• Headache
• Joint pain
• Loss of energy
• Muscle aches and stiffness
• Problems with balance
• Shaking chills
• Shortness of breath

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 culturesBronchoscopy
• Chest x-ray
• Complete blood count (CBC), including white blood cell countESR (sed rate)
• Liver blood tests
• Tests and cultures on sputum to identify 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 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

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.