Epidemiology of legionella pneumonia and factors associated with legionella-related mortality at a tertiary care center.

Legionella pneumophila is an important pathogen that may cause nosocomial and community-acquired pneumonia in patients with normal or altered immunity. The epidemiology of 40 cases of legionella pneumonia in patients hospitalized between 1986 and 1994 was studied. Fourteen patients (35%) were solid organ transplant recipients. The calculated annual incidence of L. pneumophila infection was highest among lung transplant recipients (2.07 cases per 1,000 transplant-years). There was a trend toward reduced mortality rates and less severe disease among transplant patients vs. nontransplant patients: mortality rate, 36% vs. 54%; incidence of intubation, 50% vs. 69%; rate of concurrent infections, 29% vs. 38%; and overall rate of complications, 86% vs. 96%; respectively. In a multivariate analysis, factors independently associated with an increased mortality rate were nosocomial acquisition, need for intubation, formation of lung abscess or cavitation, and presence of pleural effusion. Thus, despite differing host immune responses, the most important prognostic factors affecting the outcome of legionellosis are nosocomial acquisition and the development of pulmonary complications.