Pulmonary Nocardia otitidiscaviarum in immunocompetent individuals: a case series and literature review.

Nocardia are filamentous, Gram-positive, aerobic bacteria widely distributed in diverse environments. Nocardia otitidiscaviarum, first isolated from the middle ear of guinea pigs, is an opportunistic pathogen. Nocardia primarily infects immunocompromised hosts, However, recently there is an increasing incidence in immunocompetent individuals. Pulmonary nocardiosis is commonly caused by N. asteroides, Nocardia otitidiscaviarum pulmonary infections remain exceptionally rare. Here, we report four cases of Nocardia otitidiscaviarum infection of lung in immunocompetent individuals, including one with rare disseminated involvement of both brain and kidneys. Patients presented mostly with varied manifestations, most commonly fever, chest and back pain, and dyspnea. All patients were definitively diagnosed by either culture methods or next-generation sequencing technology. Chest computed tomography imaging revealed characteristic findings: three cases demonstrated high-density opacities (with one case additionally showing mediastinal lymphadenopathy), while one case presented with cavitary lesions accompanied by pleural effusion. Prompt administration of trimethoprim-sulfamethoxazole following rapid diagnosis effectively resolved the infection. Furthermore, in order to comprehensively characterize Nocardia otitidiscaviarum infection, we performed a systematic literature review. Our study aims to enhance clinicians’ awareness of a relatively rare pulmonary Nocardia otitidiscaviarum infection, thus providing some reference for early diagnosis and timely therapeutic intervention.Clinical trial numberNot applicable.