Clinical significance of Mycobacterium szulgai isolates from respiratory specimens

Background: The clinical relevance of Mycobacterium szulgai respiratory isolates has been controversial. The aim of this study was to determine the clinical significance of M. szulgai isolates from respiratory specimens and to identify the clinical features and outcomes of M. szulgai lung disease. Methods: We reviewed the medical records of 30 patients from whom M. szulgai was isolated between 2001 and 2010 at the Samsung Medical Center (Seoul, Korea). Results: Of the 30 patients, 13 (43%) met the American Thoracic Society diagnostic criteria and were thus likely to have true M. szulgai lung disease. Approximately 57% (17/30) of M. szulgai isolates were recovered only once from patients with other pulmonary diseases, such as pulmonary tuberculosis and other non-tuberculous mycobacterial lung diseases. The 13 patients with M. szulgai lung disease included 12 men (92%), and the median age was 63 y. Among them, 7 (54%) were current smokers and 7 (54%) had a history of previous treatment for tuberculosis. Eight (62%) patients had the fibrocavitary form of M. szulgai lung disease. Nine (69%) patients received anti-mycobacterial treatment for a median duration of 8 months. Conversion to negative cultures was documented in all patients. There was no recurrence or disease-related mortality. Conclusions: Because the isolated M. szulgai from respiratory specimens could be regarded as pathogenic in less than 50% of cases, strict adherence to the recommended diagnostic criteria of non-tuberculous mycobacterial lung disease is essential.