Legionnaire’s disease is a form of bacterial pneumonia that may occur in sporadic isolated cases or as a localized epidemic affecting groups of people. Symptoms develop within two days to a week after infection. Progressively severe pneumonia frequently occurs soon thereafter.

This is followed by either a gradual recovery or by progressively worsening congestion in the lungs that causes serious breathing difficulty. (In a milder form of the disease known as Pontiac syndrome, symptoms subside in a few days, although fatigue may persist for several weeks.)

The prognosis for Legionnaire’s disease largely depends on the age and the general health of the patient. Younger people usually recover fully, while the elderly or those in poor health are at risk for potentially fatal respiratory failure.

Legionnaire’s disease most often affects those who are middle-aged or older and is most prevalent in late summer or early fall. Immunosuppressed patients (those on certain medications, such as corticosteroids, or who have undergone organ transplantation) are at increased risk for acquiring Legionnaire’s disease.

What Causes Legionnaire's Disease?

  • Legionnaire’s disease is most often caused by the Legionella pneumophila bacterium. Most outbreaks of the disease occur when these bacteria contaminate the air-conditioning or hot-water systems of large public buildings and are transmitted via airborne vapor droplets. Outbreaks have also been described in hospitals. The infection does not spread from person to person.
  • Smoking and excessive alcohol consumption increase the risk of infection among those exposed to the bacterium.
  • Many chronic illnesses, such as kidney failure, emphysema or diabetes mellitus, increase the risk; immunosuppressed patients are also at increased risk.

Symptoms of Legionnaire's Disease

  • Headache
  • High fever and shaking chills
  • Muscle aches and stiffness
  • Dry cough in early stages; blood-streaked cough with sputum later
  • Shortness of breath
  • Chest pain
  • Diarrhea
  • Nausea and vomiting
  • Mental confusion; disorientation
  • Delirium
  • Fatigue
  • Loss of appetite

Legionnaire's Disease Prevention

  • Cooling and heating systems should be cleaned and inspected regularly and all filters changed as needed.

Diagnosis of Legionnaire's Disease

  • Patient history and physical examination are needed for proper diagnosis of pneumonia.
  • A culture of respiratory mucus may be taken.
  • Blood cultures and/or a urine specimen may also be taken.
  • A chest x-ray will be done to diagnose pneumonia or lung infection.
  • A lung biopsy may be performed (rarely).
  • Urine tests may also be performed to check for Legionella proteins in the urine.

How to Treat Legionnaire's Disease

  • Hospitalization is usually required.
  • A macrolide antibiotic (such as azithromycin or clarithromycin) or a fluoroquinolone antibiotic is often given intravenously. This usually alleviates symptoms quickly. Once clinical improvement occurs, antibiotic therapy is continued orally for 10 to 21 days.
  • Intravenous replenishment of fluids and electrolytes (essential mineral salts) may be required.
  • Aspirin or aspirin-like drugs are used to reduce fever and ease discomfort.
  • Supplementary oxygen may be administered, or in severe cases, a mechanical respirator may be required.

When to Call a Doctor

  • If you develop the symptoms of Legionnaire’s disease, call your doctor immediately.
  • If you believe you have been exposed during an outbreak of Legionnaire’s disease, contact your doctor or the public health department.


Johns Hopkins Symptoms and Remedies: The Complete Home Medical Reference

Simeon Margolis, M.D., Ph.D., Medical Editor

Prepared by the Editors of The Johns Hopkins Medical Letter: Health After 50

Updated by Remedy Health Media

Publication Review By: the Editorial Staff at Healthcommunities.com

Published: 26 Oct 2011

Last Modified: 12 Feb 2015