Simultaneous infection with Legionella pneumophila and Pittsburgh pneumonia agent. Clinical features and epidemiologic implications.

Nosocomial pneumonia caused simultaneously by two organisms, Legionella pneumophila and the Pittsburgh pneumonia agent, was documented in seven patients in one institution. In all seven cases, both organisms were demonstrated by isolation from culture or visualization by direct immunofluorescence. Four patients died as a result of pneumonia, including two who received erythromycin therapy. The hospital water distribution system appeared to be the reservoir for both L. pneumophila and Pittsburgh pneumonia agent. These seven cases constituted 26.9 percent and 17.9 percent of the cases of Pittsburgh pneumonia agent and Legionnaires' disease, respectively, at one institution. Given this relatively high incidence of dual infection, it is likely that the mode of transmission for both organisms is identical. Dual infection may account for some cases of antibody response to more than one Legionella species. Historical parallels of the discovery of L. pneumophila and Pittsburgh pneumonia agent are reviewed.