MedlinePlus Medical Encyclopedia: Legionnaire's disease

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Legionnaire's disease

Contents of this page:
Illustrations Alternative names Definition Causes, incidence, and risk factors Symptoms Signs and tests	Treatment Expectations (prognosis) Complications Calling your health care provider Prevention

Illustrations

Legionnaires' disease organism, legionella

Alternative names Return to top

Legionella pneumonia; Pontiac fever

Definition Return to top

Legionnaire's disease is an acute respiratory infection caused by the bacterium Legionella pneumophila, which can cause a broad spectrum of disease from mild cough and fever to a serious pneumonia.

Causes, incidence, and risk factors Return to top

The bacteria that cause Legionnaire's disease have been found in water delivery systems and can survive in the warm, moist, air conditioning systems of large buildings including hospitals. The infection is transmitted through the respiratory system. Person-to-person spread has not been proved.

From the onset of symptoms, the condition typically worsens during the first 4 to 6 days, with improvement starting in another 4 to 5 days. Most infection occurs in middle-aged or older people, although it has been reported in children. Typically, the disease is less severe in children.

Risk factors include cigarette smoking; underlying diseases such as renal failure, cancer, diabetes, or chronic obstructive pulmonary disease; people with suppressed immune systems from chemotherapy, steroid medications, or diseases such as cancer and leukemia; alcoholism; being middle-aged or elderly, and in people on a ventilator for extended periods.

Symptoms Return to top

Muscle aches and stiffness
Joint pain
Loss of energy
General discomfort, uneasiness, or ill feeling (malaise)
Headache
Fever
Shaking chills
Nonproductive cough
Coughing of blood
Shortness of breath
Chest pain
Diarrhea
Ataxia (lack of coordination)

Signs and tests Return to top

Listening to the chest with a stethoscope reveals fine crackles.
Sputum direct fluorescent antibody staining shows Legionella.
The causative organism may be cultured from the airway.
Urine tests for the bacteria (urine antigen test) may be positive.
Chest X-ray shows pneumonia.
Arterial blood gas analysis may show low concentrations of oxygen.
CBC shows an increased white blood cell count.
Erythrocyte sedimentation rate is increased.
Low serum sodium.
Liver function tests may show moderate elevation.

Treatment Return to top

The goal of treatment is to eliminate the infection with antibiotics. Treatment is started as soon as Legionnaire's disease is suspected, without waiting for confirmation by culture results.

The antibiotic commonly used is quinolone (ciprofloxacin, levofloxacin, moxifloxacin, or gatifloxacin) or a macrolide (azithromycin, clarithromycin, or erythromycin).

Supportive treatment includes hospitalization for fluid and electrolyte replacement and oxygen administration by mask or by mechanical ventilation, if the respiratory system becomes severely compromised by the infection.

Expectations (prognosis) Return to top

The overall death rate for those with pneumonia is about 15%, and the death rate increases in those with underlying diseases. The mortality for patients who develop Legionnaire's disease while hospitalized is close to 50%, especially when antibiotics are started late.

Complications Return to top

Some complications include respiratory failure requiring use of a respirator.

Calling your health care provider Return to top

Call your health care provider if breathing difficulties develop.

Prevention Return to top

Active surveillance of infections that were acquired within a hospital can lead to the treatment of contaminated water delivery systems. Detection and treatment of sources outside hospitals usually occurs during or after an epidemic has happened.

Update Date: 8/11/2003

Updated by: Daniel Levy, M.D., Ph.D., Infectious Diseases, Greater Baltimore Medical Center, Baltimore, MD. Review provided by VeriMed Healthcare Network.

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright 2002 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.