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Nontuberculous Mycobacterial Pulmonary Disease from Mycobacterium hassiacum, Austria

The clinical relevance of newly described nontuberculous mycobacteria is often unclear. We report a case of pulmonary infection caused by Mycobacterium hassiacum in an immunocompetent patient in Austria who had chronic obstructive pulmonary disease. Antimicrobial drug susceptibility testing showed low MICs for macrolides, aminoglycosides, fluoroquinolones, tetracyclines, imipenem, and linezolid.

C urrently, >170 species of nontuberculous mycobacteria (NTM) are recognized (1), most considered nonpathogenic to humans. However, some NTM can cause severe pulmonary disease. We recently observed a case of NTM pulmonary disease (NTM-PD) in Austria that was caused by Mycobacterium hassiacum.
In January 2019, a 62-year-old man was admitted to the outpatient clinic at Kepler University Hospital in Linz, Austria, having had dry cough and progressive dyspnea for several months. No weight loss or night sweats were reported. He had a medical history of chronic obstructive pulmonary disease with severe emphysema because of cigarette smoking. The patient had no history of tuberculosis or NTM-PD and was unaware of any contact with persons with mycobacterial infections.
Chest radiograph showed new consolidations in the right and left upper lung lobes compared with images obtained 1 year before. We performed a high-resolution computed tomography scan of the chest and an 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET) scan that indicated metabolic activity consistent with an inflammatory process ( Figure). In addition, results of tests for serum lung cancer biomarkers, including CA 19-9, CEA (carcinoembryonic antigen), CYFRA 21-1, and NSE (neuron-specific enolase), and for HIV-1 and HIV-2 were negative. Transbronchial catheter aspiration from the posterior lung segment of the right upper lung lobe showed no microscopic evidence of bacteria, acid-fast bacilli, or fungi. The result from a PCR assay (Mycobacterium tuberculosis PCR kit; Geneproof, https://www.geneproof.com) for M. tuberculosis complex DNA was negative. Results from bacterial and fungal cultures were unremarkable. Because the patient was at high risk for developing pneumothorax due to severe emphysema, no transbronchial biopsy was taken during initial bronchoscopy.
The clinical relevance of newly described nontuberculous mycobacteria is often unclear. We report a case of pulmonary infection caused by Mycobacterium hassiacum in an immunocompetent patient in Austria who had chronic obstructive pulmonary disease. Antimicrobial drug susceptibility testing showed low MICs for macrolides, aminoglycosides, fluoroquinolones, tetracyclines, imipenem, and linezolid.

RESEARCH LETTERS
Mycobacterial culture results of the transbronchial catheter aspirate were negative after 8 weeks of incubation. Consequently, we performed a computed tomography-guided needle biopsy of the cavitary lesion in the right upper lung lobe. Histological results showed granulomatous inflammation with focal eosinophilic necrosis. We detected no atypical cells, acid-fast bacilli, or fungal hyphae and subsequent immunohistochemistry testing revealed no evidence of malignant disease.
Since M. hassiacum was described as a new species in 1997, 3 cases of suspected infections caused by M. hassiacum have been reported in the medical literature (6). So far, M. hassiacum has been reported as the causative agent for peritonitis and cystitis (7,8). In addition, M. hassiacum was recently isolated from a respiratory sample in a patient in Germany with exacerbation of chronic obstructive pulmonary disease (9). However, that patient likely did not have NTM-PD because M. hassiacum was isolated in only 1 of 3 sputum samples, he showed no NTM-specific radiological abnormalities in a chest radiograph, and his clinical condition improved rapidly without any antimycobacterial treatment.
In contrast, the patient we report fulfills 3 diagnostic criteria of NTM-PD: 1) an NTM-specific radiologic pattern characterized by new nodules in both upper lung lobes in a high-resolution computed tomography scan of the chest, 2) a positive culture result from a sterile computed tomography-guided needle biopsy, as well as typical mycobacterial histopathologic features including granulomatous inflammation, and 3) exclusion of other disorders including pulmonary tuberculosis or lung cancer (10).
In conclusion, detection of M. hassiacum in patients fulfilling the criteria for NTM-PD should be considered a potentially relevant finding. Further studies are needed to evaluate the precise role of M. hassiacum as an emerging mycobacterial pathogen.