Pulmonary Nocardiosis Caused by Nocardia sputorum Identified via 16S rRNA Gene Sequencing: A Case Report.

Nocardia sputorum, a novel Nocardia species discovered in Japan in 2023, has not been reported to infect humans. Here, we report a case of pulmonary nocardiosis in a 70-year-old immunocompetent woman infected with N. sputorum. The patient presented to the hospital with a chief complaint of weight loss. She worked at a fruit sorting facility where she was exposed to dust. Chest computed tomography revealed a single cavity and diffuse nodular opacities in both lungs. Nocardia species was isolated from tracheal sputum and bronchial lavage fluid and identified as N. sputorum via 16S rRNA gene sequencing. The patient was treated with oral sulfamethoxazole and trimethoprim but developed oral mucositis on the 12th day of treatment. Consequently, minocycline was prescribed, and the patient's condition improved after a six-month course of treatment. To our knowledge, this is the first reported case of pulmonary nocardiosis caused by N. sputorum in humans. Accurate species identification and antimicrobial susceptibility tests will be necessary to prescribe appropriate treatment for Nocardia infections.