Diagnostic Challenges of Nocardia beijingensis Pneumonia: a Microbiological and Multidisciplinary Analysis in an Immunocompetent Patient.

BACKGROUND: Nocardia species are ubiquitously distributed in natural environments and typically cause opportunistic infections through inhalation into the respiratory tract or invasion of damaged skin or mucosal barriers. The clinical manifestations and imaging findings of Nocardia infections often lack specificity, which can lead to misdiagnosis or delayed diagnosis. However, etiological examinations (e.g., microbiological culture, PCR, or metagenomic sequencing) can facilitate accurate diagnosis and prompt therapeutic intervention. METHODS: In November 2024, a 74-year-old female presented with a cough and sputum production. Sputum and bronchoalveolar lavage fluid (BALF) samples were collected by the Department of Respiratory and Critical Care Medicine and subjected to Gram staining, modified acid-fast staining, and cultured on blood agar plates at a constant temperature of 35℃ with 5% CO2. Gram staining of sputum smears revealed Gram-positive bacilli with right-angle branching, which were also positive on modified acid-fast staining. After 48 hours of culture on blood agar, dry, white colonies were observed. Finally, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) identified the isolate as Nocardia beijingensis (N. beijingensis), which was further confirmed by targeted next-generation sequencing (tNGS). RESULTS: The patient was definitively diagnosed with Nocardia pneumonia and achieved complete recovery following antibiotic therapy. After hospitalization, the patient was treated with piperacillin sodiumtazobactam sodium (4.5 g, Q8h) combined with compound sulfamethoxazole (2 tablets, Q6h), along with adjunctive symptomatic and supportive management such as antitussive agents and gastric protection. CONCLUSIONS: Nocardia pneumonia remains a clinical challenge due to its rarity and nonspecific symptoms. A systematic analysis of laboratory findings, definitive pathogen identification, and therapeutic interventions in this case offers valuable insights to improve diagnostic proficiency for Nocardia-related pulmonary infections and enhance patient prognosis.