Pulmonary disease caused by Mycobacterium shimoidei in an immunocompetent adult: a case report

Mycobacterium shimoidei is a rare, slow-growing nontuberculous mycobacterium (NTM) primarily reported in the Asian Pacific region and Japan. It is typically associated with severe pulmonary disease in older patients with pre-existing structural lung damage. We report a rare case of cavitary NTM-pulmonary disease (NTM-PD) caused by M. shimoidei in a 30-year-old male from Austria. In April 2022, a 30-year-old male smoker presented with an incidental right upper lobe cavity on a routine chest X-ray. Computed tomography (CT) revealed tree-in-bud infiltrates, mild localized emphysema, and two thick-walled cavitary lesions. Sputum cultures were positive for M. shimoidei. Although the patient only reported mild cough, treatment was initiated due to the presence of cavitary disease. The patient received an initial regimen of azithromycin, ethambutol, and rifampicin that was modified after 12 months by replacing rifampicin with linezolid (total treatment duration = 24 months). At the 36-month follow-up, the patient remained asymptomatic without signs of disease recurrence. This case demonstrates that M. shimoidei may cause clinically relevant NTM-PD in individuals without known risk factors outside of traditional endemic regions. A multi-drug regimen including azithromycin, ethambutol, and linezolid may be an effective treatment for M. shimoidei . The overall benefit of early treatment in oligosymptomatic cases is not yet established but can be hypothesized by the relatively poor prognosis in earlier case reports.