Legionella Pneumonia in the Modern Era: Clinical Features and Predictors of Mortality.

Abstract

Background: Legionella pneumonia is an important cause of severe pneumonia, yet contemporary data describing its clinical phenotype, diagnostic patterns, and outcomes in the modern era are limited.

Methods: We conducted a retrospective multicenter cohort study of adults with laboratory-confirmed Legionella pneumonia across an integrated health system between January 2019 and September 2025. The primary outcome was 30-day mortality. Severe disease was defined as having a requirement for high-flow nasal cannula, noninvasive ventilation, mechanical ventilation, or extracorporeal membrane oxygenation (ECMO). Univariate and multivariable logistic regression were used to identify predictors of mortality and severe disease.

Results: There were 344 patients with laboratory-confirmed Legionella pneumonia during the study period. The median age was 66.6 years, and 45.1% were immunocompromised. Most patients required hospital admission (94.2%), with 36.1% admitted to the intensive care unit; 22.7% required mechanical ventilation and 1.5% ECMO. Thirty- and 90-day mortality were 11.9% and 16.6%, respectively. In multivariable analysis, cirrhosis (OR 10.2, 95% CI 2.15-48.3, P = .003), immunocompromised status (odds ratio [OR] 2.24, 95% CI 1.05-4.77, P = .036), age (OR 1.03, 95% CI 1.00-1.06, P = .031), and lymphopenia at presentation (OR 2.09, 95% CI 1.02-4.24, P = .043) were independently associated with increased 30-day mortality. Among patients who were polymerase chain reaction (PCR) or culture positive, urinary antigen testing was positive in only 25.6%.

Conclusions: Legionella pneumonia was associated with substantial short-term mortality. Cirrhosis, age, immunocompromised status, and lymphopenia at presentation emerged as independent predictors of 30-day mortality, underscoring the importance of host vulnerability in determining outcomes.