Case Report: Cavitary Legionella pneumophila pneumonia in a kidney transplant recipient: mNGS-guided diagnosis and prolonged combination therapy

Legionella pneumophila is an uncommon but potentially life-threatening cause of pneumonia in solid organ transplant (SOT) recipients. Diagnosis is challenging due to nonspecific features and the limited sensitivity of conventional assays. Metagenomic next-generation sequencing (mNGS) offers unbiased detection and may be particularly valuable in immunocompromised hosts with refractory pneumonia. We report the first documented case in Asia of cavitary Legionella pneumonia in a kidney transplant recipient. A 60-year-old man presented with fever and bilateral pulmonary nodules 5 months post-transplant. Despite empirical antifungal and antibacterial therapy, his condition progressed radiologically to cavitary disease. Bronchoalveolar lavage fluid mNGS identified abundant L. pneumophila reads, confirming the diagnosis. Initial azithromycin monotherapy achieved transient improvement but failed to prevent radiological progression. Escalation to prolonged dual therapy with azithromycin and levofloxacin resulted in rapid symptomatic relief, progressive cavity regression on serial computed tomography, and preserved allograft function. Sequential blood-based mNGS demonstrated declining pathogen reads paralleling recovery. This brief research report emphasizes three practice points for SOT recipients with refractory pneumonia: (1) early mNGS can shorten time-to-diagnosis when routine tests are inconclusive; (2) Legionella infection may manifest with atypical cavitary lesions in immunocompromised hosts, warranting scheduled imaging even when symptoms improve; and (3) prolonged macrolide–fluoroquinolone combination therapy may be required for severe or non-resolving cases. Together with our literature review, this case expands understanding of the radiological spectrum, diagnostic strategies, and therapeutic considerations of Legionella pneumonia in transplant populations.