A Case of Asymptomatic Pulmonary Nocardia cyriacigeorgica Infection With Mild Diabetes Mellitus

Nocardiosis is a relatively rare opportunistic infection, ranging from localized to systemic diseases, commonly occurring in immunocompromised patients with high mortality rates. We present a case of a 61-year-old man who received medical treatment for type 2 diabetes mellitus and underwent a physical examination that showed abnormal chest shadows on radiography. Chest computed tomography revealed bronchiectasis and infiltration in the left lower lobe. Nocardia spp. was detected in the bronchial washes, and he was started on sulfamethoxazole-trimethoprim under the diagnosis of pulmonary nocardiosis. 16S ribosomal RNA gene sequencing analysis identified the species as Nocardia cyriacigeorgica. His pulmonary lesions successfully improved after treatment for six months. Pulmonary nocardiosis often presents with symptoms such as hemoptysis and blood-tinged sputum, and bronchiectasis has been identified as an underlying condition. Even in hosts without underlying immunocompromising conditions, Nocardia spp. can be a causative microorganism of pulmonary infections, and it should be considered in the differential diagnoses.