Legionella species as hospital-acquired respiratory pathogens

Nosocomial pneumonia caused by legionella is an increasingly recognized entity. Legionella sp responsible for documented nosocomial disease include Legionella pneumophila, Tatlockia micdadei, Legionella bozemanii, Legionella dumoffi and Legionella oakridgensis. The clinical presentation is nonspecific although diarrhea occurs frequently. Hyponatremia occurs significantly more frequently in legionnaires' disease than pneumonias caused by other agents. Chest roentgenographic findings are nonspecific, although cavitation can be seen in immunosuppressed patients. Laboratory methods require the use of direct fluorescent antibody (DFA) stains, culture using selective media, serologic testing, and detection of antigen in urine. The DFA test is not sensitive; however, it does correlate with the severity of disease. Culture from sputa is now feasible. Bronchoalveolar lavage is a promising technique for obtaining specimens. The ideal specimen for culture is that obtained by transtracheal aspiration, which bypasses oropharyngeal contamination. Combination therapy of erythromycin and rifampin is recommended for selected patients. Because the source of the organism is the hospital water distribution system, we recommend routine environmental surveillance, especially in hospitals in which organ transplants are performed. The role of cooling towers as a vector for dissemination of the organism is disputed. Disinfection of the water supply can be accomplished by using heat eradication. Chlorination has generally proven unsatisfactory because of organism persistence as well as corrosive damage to the plumbing system from the chlorine. Both physician awareness and availability of specialized laboratory testing are necessary for the detection of cases.