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Updated: Nov 24, 2025
Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection
Published on: November 22, 2013
Risk Factors, Management, and Outcomes of Legionella Pneumonia in a Large, Nationally Representative Sample
Joshua Allgaier1, Tara Lagu2, Sarah Haessler3
1Department of Medicine, University of Massachusetts Medical School-Baystate, Springfield, MA.
Background:
American Thoracic Society/Infectious Diseases Society of America guidelines recommend against routine Legionella pneumophila testing, but recommend that hospitalized patients with community-acquired pneumonia receive empiric treatment covering Legionella. Testing, empiric treatment, and outcomes for patients with Legionella have not been well described.
Research Question:
Is testing for Legionella pneumophila appropriate, and could it impact treatment?
Study Design And Methods:
We conducted a large retrospective cohort analysis using Premier Healthcare Database data from 2010 to 2015. We included adults with a principal diagnosis code for pneumonia (or a principal diagnosis of respiratory failure or sepsis with secondary diagnosis of pneumonia) if they also received treatment for pneumonia on hospital days 1-3. We categorized Legionella-tested patients by test result, identified patient characteristics associated with testing and test result, and examined seasonal and regional patterns of Legionella pneumonia (LP) diagnoses. Empiric therapy for LP was defined as a macrolide, quinolone, or doxycycline, administered on each of the first two hospital days.
Results:
Of 166,689 eligible patients, 43,070 (26%) were tested for Legionella, and 642 (1.5%) tested positive. Although only 36% of tests were ordered from June to October, 70% of positive test results occurred during this time. Only 30% of patients with hyponatremia, 32% with diarrhea, and 27% in the ICU were tested. Of patients with positive test results, 495 of 642 (77%) had received empiric Legionella therapy. Patients with LP did not have more severe presentation. They had more frequent late decompensation, but similar mortality to patients without LP.
Interpretation:
Legionella is an uncommon cause of community-acquired pneumonia, occurring primarily from late spring through early autumn. Testing is uncommon, even among patients with risk factors, and many patients with positive test results failed to receive empiric coverage for LP.
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