Pulmonary infections due to Legionella in immunocompromised patients.

At present, 11 different species of Legionella have been implicated in human disease. It has become apparent that disease caused by Legionella is acquired from a variety of environmental sources and that water is the factor that links many of them. Patients who are immunosuppressed, such as individuals receiving cancer chemotherapy or therapy designed to prevent organ rejection, are particularly susceptible to such environmental sources. It appears that intact cell-mediated immunity is more important in host defense than are adequate numbers of granulocytes or immunoglobulin concentrations. Diagnostic steps should be undertaken in all patients developing nosocomial pneumonia who present with a picture suspicious for this disorder. In the meantime, appropriate antimicrobial therapy with erythromycin and rifampin should be begun. If clusters of cases are detected in a hospital, immediate steps should be taken to attempt to isolate the organism from any aqueous environmental sources, and if found appropriate, steps taken. Awareness of the threat of legionnaires' disease must be maintained among clinicians and hospital epidemiologists because it is unlikely that the problem of nosocomial legionnaires' disease will disappear.