Legionnaires’ disease
An acute bronchopneumonia, legionnaires’ disease is produced by a fastidious, gram-negative bacillus. This disease may occur epidemically or sporadically, usually in late summer or early fall. Its severity ranges from a mild illness, with or without pneumonitis, to multilobar pneumonia, with a mortality as high as 15%. A milder, self-limiting form (Pontiac fever) subsides within a few days, but leaves the patient fatigued for several weeks; this form mimics legionnaires’ disease, but produces few or no respiratory symptoms, no pneumonia, and no fatalities.
Causes
The cause of legionnaires’ disease, Legionella pneumophila, is an aerobic, gram-negative bacillus that’s probably transmitted by an airborne route. With past epidemics, it has spread through cooling towers or evaporation condensers in air-conditioning systems. However, Legionella bacilli also flourish in soil and excavation sites. The disease doesn’t spread from person to person.
Legionnaires’ disease is more common in men than in women and is most likely to affect:
middle-aged to elderly people
immunocompromised people (particularly those receiving a corticosteroid, for example, after a transplant) or those with lymphoma or other disorders
associated with delayed hypersensitivity
patients with a chronic underlying disease, such as diabetes, chronic renal failure, or chronic obstructive pulmonary disease
alcoholics
cigarette smokers (three to four times more likely to develop legionnaires’ disease than nonsmokers).
