Legionnaires Disease

A progressive and potentially fatal atypical pneumonia caused by the inhalation of water aerosols containing Legionella bacteria.


caused by infection with a gram negative, aerobic bacteria belonging to the genus Legionella. Over 90% of legionellosis cases are caused by Legionella pneumophila, a ubiquitous aquatic organism that thrives in temperatures between 25 and 45 °C.

Two prognosis:

  1. Legionnaires’ disease, “Legion Fever” , is the more severe form of the infection and produces pneumonia.
  2. Pontiac fever is caused by the same bacterium, but produces a milder respiratory illness without pneumonia which resembles  acute influenza.

Manifestation: Signs and Symptoms:

Legionnaires’ disease

  1. fever
  2. chills
  3. cough, which may be dry or productive
  4. muscle aches
  5. headache
  6. tiredness
  7. loss of appetite (anorexia)
  8. loss of coordination (ataxia)
  9. occasionally diarrhea and vomiting.


  1. Laboratory tests may show that patients’ renal functions, liver functions and electrolytes are deranged
  2. hyponatremia.
  3. Chest X-rays often show pneumonia with bi-basal consolidation.
  4. It is difficult to distinguish Legionnaires’ disease from other types of pneumonia by symptoms or radiologic findings alone.

Chest X-ray of pneumonia patient

Treatment: antibiotics



  1. Persons with Pontiac fever experience fever and muscle aches without pneumonia. They generally recover in 2 to 5 days without treatment.
  2. The time between the patient’s exposure to the bacterium and the onset of illness for Legionnaires’ disease is 2 to 10 days; recovery duration is longer with the additional use of antibiotics.

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