Risk factors, management, and outcomes of legionella pneumonia in a large nationally-representative sample

Background: ATS/IDSA guidelines recommend against routine Legionella pneumophila testing but that hospitalized patients with community-acquired pneumonia (CAP) 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 2010-2015 data from the Premier Healthcare Database. 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 by hospital day 1. 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 2 hospital days. Results: Of 166,689 eligible patients, 43,070 (26%) were tested for Legionella, and 642 (1.5%) tested positive. While only 36% of tests were ordered from June-October, 70% of positive tests occurred during this time. Only 30% of patients with hyponatremia and 32% with diarrhea and 27% in the ICU were tested. Of positive patients, 495/642 (77%) had received empiric Legionella therapy. LP patients did not have more severe presentation. They had more late decompensation, but similar mortality to patients without LP. Interpretation: Legionella is an uncommon cause of CAP, occurring primarily from late spring through early autumn. Testing is uncommon, even among patients with risk factors, and many positive patients failed to receive empiric coverage for LP