Pulmonary infection caused by Nocardia cyriacigeorgica and influenza A virus coinfection in an immunocompetent patient

Rationale: Pulmonary nocardiosis (PN) is an opportunistic infection caused by Nocardia species. It is characterized by a lack of specificity in both clinical symptoms and imaging findings. Most cases occur in individuals with compromised immune systems or underlying pulmonary diseases. In contrast, our patient did not present with any of these risk factors. Patient concerns: A 60-year-old immunocompetent male was admitted with a 5-month history of recurrent cough and expectoration. His respiratory symptoms worsened, and he developed a fever 9 days prior to hospitalization. Diagnoses: Nocardia cyriacigeorgica was identified in the sputum culture, as well as in the targeted next-generation sequencing and culture of the bronchoalveolar lavage fluid, while influenza A virus was detected by nucleic acid detection. Interventions: Along with antiviral therapy with peramivir, a combination antibiotic regimen of trimethoprim-sulfamethoxazole (TMP-SMX), etimicin, and meropenem was administered during hospitalization. Following discharge, oral TMP-SMX was continued as maintenance therapy. Outcomes: Regular follow-ups with the patient revealed that subsequent chest computed tomography (CT) scans showed a gradual reduction in the extent of the lesions, and the patient demonstrated a good clinical response and radiological improvement. Lessons: This case highlights the diagnostic complexity of PN. The radiological manifestations are diverse, commonly including pulmonary consolidation, nodules, and cavities, making it difficult to differentiate from other diseases. Early, precise diagnosis and prompt combined therapy are of vital importance in severe Nocardia pulmonary infection.