A rare case of Legionella bozemanae leading to necrotizing pneumonia in an immunocompromised patient: a case study

Abstract

Legionella bozemanae is a rare organism of Legionella species that can cause mild fever to severe pulmonary pneumonia known as Legionnaires’ disease. It can also cause extra-pulmonary infections, particularly in immunocompromised patients although deadly outcome in immunocompetent has also been reported. Diagnosis is often delayed due to limitations of conventional methods such as culture, serology, and urinary antigen testing, making newer molecular methods more valuable for early detection. We report the case of a 68-year-old male with history of relapsed acute myeloid leukemia (AML) and Sweet’s syndrome who presented with worsening dyspnea to emergency department. For evaluation, CT chest and the Karius test were performed. Which confirmed L. bozemanae infection and lobar consolidation. Despite multiple courses of broad-spectrum antimicrobials, including fluoroquinolones (Levofloxacin), macrolides (Azithromycin), and beta-lactams (Amoxi-clav), his condition deteriorated. Repeat CT scan showed progressive bilateral consolidation with cavitation, this suggested progressing to necrotizing pneumonia. Invasive procedures were deferred due to profound pancytopenia. Escalation of antibiotics were done but the patient eventually succumbed to his illness. This case presents the diagnostic and therapeutic challenges of L. bozemanae infection in immunocompromised patient. Routine diagnostic methods often fail to identify this organism, whereas next-generation sequencing plasma cfDNA, was valuable in confirming the pathogen. However, treatment response was poor, likely because of profound immunosuppression and possible antimicrobial resistance, consistent with previously reported cases in the literature. L. bozemanae infection, though rare, should be considered in immunocompromised patients with progressive pneumonia unresponsive to standard therapy. Early use of advanced molecular diagnostics may facilitate timely diagnosis and treatment. Management may require combination antimicrobial therapy, as monotherapy has been associated with resistance and relapse. Aggressive management is recommended, as the infection can lead to lung tissue necrosis, as seen in our case.