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Legionnaires' Disease

Legionnaires' disease is an acute bronchopneumonia produced by a gram-negative bacillus. This disease was named for 221 persons (34 of whom died) who became ill during an American Legion convention in Philadelphia in July 1976. Outbreaks, usually in late summer and early fall, may be epidemic or confined or a few cases. The disease may range from a mild illness (with or without pneumonitis) to serious multilobed pneumonia with mortality as high as 15%.

Pontiac fever is a less severe, self-limiting form of the illness that subsides within a few days but leaves the patient fatigued for several weeks. This disorder is caused by the same organism as Legionnaires' disease but produces few or no respiratory symptoms, no pneumonia, and no fatalities.

Legionnaires' disease is more common in men man in women and is most likely to affect:

  • elderly people
  • immunocompromised patients (particularly those receiving corticosteroids after transplantation) or those with lymphoma or other disorders associated with impaired humoral immunity
  • patients with chronic underlying disease, such as diabetes, chronic renal failure, or chronic obstructive pulmonary disease
  • alcoholics
  • cigarette smokers (who are three to four times more likely to contract Legionnaires' disease than non-smokers).


The bacteria that cause Legionnaires' disease are found in warm, stagnant water and the soil it seeps into. People inhale the bacteria when it becomes airborne, usually through air conditioners, humidifiers, shower heads and faucets, whirlpool spas, and even the water misters found in grocery stores. The bacteria has been found in soil and groundwater at construction sites.

Symptoms and Signs

The symptoms of legionnaires' disease:

  1. High temperature, feverishness and chills;
  2. Cough;
  3. Muscle pains;
  4. Headache; and leading on to
  5. Pneumonia, very occasionally
  6. Diarrhoea and signs of mental confusion

Diagnostic tests

Chest X-ray typically shows patchy, localized infiltration, which progresses to multilobed consolidation (usually involving the lower lobes) and pleural effusion. In fulminant disease. chest X-ray reveals opacification of the entire lung.

Laboratory tests include various blood studies and cultures. Blood test findings may include leukocytosis; increased erythrocyte sedimentation rate; a moderate increase in liver enzyme (alkaline phosphatase, alanine aminotransferase, and aspartate aminotransferase) levels; and decreased partial pressure of oxygen and, initially, decreased partial pressure of carbon dioxide. Hyponatremia (serum sodium level less than 131 mg/L) is evident on chemistry.

Bronchial washings, blood and pleural fluid cultures, and transtracheal aspirate studies rule out other pulmonary infections. Gram staining reveals numerous neutrophils but no organism. Isolation of the organisms from respiratory secretions or bronchial washings or through thoracentesis is a definitive method of diagnosis.

Definitive tests include direct immunofluorescence of L. pneumophila and indirect fluorescent serum antibody testing. These tests compare findings from initial blood studies with findings from those done at least 3 weeks later. A convalescent serum sample showing a fourfold or greater increase in antibody titer for L. pneumophila confirms the diagnosis.


Antibiotic treatment begins as soon as Legionnaires' disease is suspected and diagnostic material is collected. Treatment need not await test results. Erythromycin and tetracycline are most effective. Azithromycin or other nerve macrolides are preferred for immunocompromised patients. For severely ill patients, a combination of rifampin and a macrolide or quinoline may be used.

Supportive therapy includes administration of antipyretics, fluid replacement, circulatory support with pressor drugs if necessary, and oxygen administration by mask or cannula or by mechanical ventilation with positive end-expiratory pressure.


The likelihood of Legionella infection can be best reduced by good engineering practices in the operation and maintenance of air and water handling systems.

Cooling towers and evaporative condensers should be inspected and thoroughly cleaned at least once a year.

Corroded parts, such as drift eliminators, should be replaced. Algae and accumulated scale should be removed.

   Pneumocystis Carinii Pneumonia
   Pseudomonas Infections
   Relapsing Fever
   Respiratory Syncytial Virus Infection
   Rocky Mountain Spotted Fever
   Roseola Infantum
   Salmonella Infection
   Scarlet Fever
   Toxic Shock Syndrome
   Vancomycin Intermittent-Resistant Staphylococcus Aureus
   Vancomycin-Resistant Enterococcus
   West Nile Encephalitis

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