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 .
Alternative Names
Legionella pneumonia; Pontiac fever
Causes, incidence, and risk factors
The bacteria 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 route. Person to person spread has not been proven. From the onset of symptoms, a worsening of the condition is typical 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 chronically ventilated patients.
Signs and tests
Listening to the chest with a stethoscope ( auscultation ) reveals fine crackles.
Sputum DFA (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
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. Erythromycin is the drug of choice. 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)
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
Some complications include respiratory failure requiring mechanical ventilation (use of a respirator).
Calling your health care provider
Call your health care provider if breathing difficulties develop.
Prevention
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.