Chest Computed Tomography Manifestations of Legionella Pneumonia in a Large Multihospital Cohort of Immunocompromised and Immunocompetent Patients

PURPOSE: To assess chest computed tomography (CT) manifestations of Legionella pneumonia (LP) in a large, well-characterized immunocompetent and immunocompromised patient cohort. MATERIALS AND METHODS: This retrospective study identified LP patients across a multicenter hospital system over 84-months. Chest CTs were reviewed for presence and distibution of ground-glass opacity (GGO), consolidation, and numerous other findings. CT findings were categorized into lobar, bronchopneumonia, atypical, and mixed patterns. Evolution on follow-up CT was assessed. RESULTS: 311/346 patients (median age 66.6 y [IQR: 55.9, 74.8]; 178 [57.2%] male) had CT examinations available. GGO (98.1%, 305/311) and consolidation (92%, 286/311) were the most prevalent findings, commonly coexisting. The segmental pattern occurred most frequently. The GGO and reverse halo signs occurred in 6.1% (19/311) and 3.5% (11/311), respectively. Follow-up CT occurred in 58.5% (182/311) (median=47.5 d), demonstrating improvement in 84.1% (153/182), worsening in 10.4% (19/182), stability in 5.5% (10/182), and new CT patterns in 12.6% (23/182). Respiratory co-infection occurred in 27.0% (84/311), commonly bacterial. Cavitation occurred in 7.1% (22/311), more frequently among co-infected patients (14.3%, 12/84) than isolated LP (4.4%, 10/227, P=0.005), even more common among immunocompromised patients (12.0% [18/150] vs. 2.5% [4/161], P=0.001), the highest prevalence among co-infected immunocompromised patients (21.3%, 10/47). Co-infection (odds ratio [OR]=3.26, 95% CI=1.33-8.00; P=0.01) and immunocompromise (OR=4.93, 95% CI=1.61-15.1; P=0.005) were independently associated with cavitation. CONCLUSIONS: LP presents nonspecifically with a multilobar segmental pattern of GGO and consolidation. Respiratory co-infection was common, often heralded by cavitation. CT findings improve after LP diagnosis.