Legionnaires’ Disease
An acute bronchopneumonia, Legionnaires’ disease is produced by a gram-negative bacillus. This disease was named for 221 persons (34 of whom died) who became ill while attending an American Legion convention in Philadelphia in July 1976. Outbreaks, usually occurring in late summer and early fall, may be epidemic or confined to a few cases. The disease may range from a mild illness (with or without pneumonitis) to serious multilobar pneumonia with mortality as high as 15%.
A less severe, self-limiting form of the illness, Pontiac fever subsides within a
few days but leaves the patient fatigued for several weeks. This disorder mimics Legionnaires’ disease but produces few or no respiratory symptoms, no pneumonia, and no fatalities.
few days but leaves the patient fatigued for several weeks. This disorder mimics Legionnaires’ disease but produces few or no respiratory symptoms, no pneumonia, and no fatalities.
Legionnaires’ disease is more common in males than in females and is most likely to affect:
middleaged or elderly people
immunocompromised patients (particularly those receiving corticosteroids after transplantation) or those with lymphoma or other disorders associated with impaired humoral immunity
patients with a chronic underlying disease, such as diabetes, chronic renal failure, and chronic obstructive pulmonary disease
alcoholics
cigarette smokers (three to four times more likely to contract Legionnaires’ disease than nonsmokers).
Causes
Legionnaires’ disease results from infection with Legionella pneumophila, an aerobic, gram-negative bacillus that is probably transmitted by air. The organism’s natural habitat seems to be water—either hot or cold. In the past, air-conditioning systems were thought to be the main source of transmission. However, public health officials have since identified water distribution systems as the primary reservoir for the organism.
Complications
Patients in whom pneumonia develops also may experience hypoxia and acute respiratory failure. Other complications include hypotension, delirium, seizures, heart failure, arrhythmias, renal failure, and shock that usually is fatal.
Assessment
The patient history may include presence at a suspected source of infection. Onset of Legionnaires’ disease may be gradual or sudden. After a 2- to 10-day incubation period (or a 1-to 2-day incubation period in Pontiac fever), the patient may report nonspecific prodromal symptoms, including diarrhea, anorexia, malaise, diffuse myalgia and generalized weakness, headache, and recurrent chills.
With Legionnaires’ disease, the patient typically reports a cough—initially nonproductive but eventually productive. He also may complain of dyspnea and chest pain or sometimes nausea, vomiting, and abdominal pain.
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