Gotway, Michael

Abstract Rationale Legionella species can cause severe community-acquired pneumonia requiring targeted antimicrobial therapy. The impact of time to effective Legionella-directed therapy on mortality is not well defined. Objectives To evaluate the association between time to effective Legionella-directed therapy and mortality in hospitalized patients with community-acquired Legionella pneumonia and to determine whether differences in treatment timing contribute to the excess mortality observed among immunocompromised patients. Methods A retrospective multicenter cohort study of adults hospitalized with laboratory-confirmed community-acquired Legionella pneumonia (2019–2025) was performed. Time from presentation to effective therapy (macrolide, fluoroquinolone, or doxycycline) was recorded. The primary outcome was 90-day mortality. Multivariable logistic regression analysis was performed, adjusting for age, SOFA-2 score (first 6 hours), and immunocompromised status. Secondary analyses included a 24-hour landmark Cox model for 90-day survival and multivariable logistic regression for 30-day mortality. Results Among 310 patients (median age 66.9 years, 44.8% immunocompromised), 90-day mortality was 17.4%. Every 6-hour delay in effective therapy was independently associated with increased 90-day mortality (adjusted OR per 6 hours: 1.11; 95% CI, 1.06–1.17; P < 0.001). Delays >24 hours were associated with worse 90-day survival (adjusted HR, 2.72; 95% CI, 1.65–4.77; P < 0.001). Time to effective therapy was also independently associated with increased odds of 30 day mortality (adjusted OR per 6 hours: 1.06; 95% CI: 1.01-1.11, p = 0.024). Immunocompromised patients experienced longer delays (median, 7.1 versus 3.3 hours; P < 0.001) and higher unadjusted 90-day mortality (22.3% versus 13.5%; P = 0.041), but immunocompromised status was not independently associated with mortality after adjusting for severity and treatment timing. Conclusion Longer time to effective Legionella-directed therapy was independently associated with increased mortality in a graded fashion. Delays were more common among immunocompromised patients, partially accounting for excess mortality in this group, suggesting that timely pathogen-directed therapy may represent a clinically important and potentially modifiable contributor to risk.

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.