Clinical significance of Mycobacterium fortuitum isolated from respiratory specimens

Although Mycobacterium fortuitum is not an uncommon organism among the non-tuberculous mycobacteria isolated from respiratory specimens, its clinical significance had not been well studied.

We identified all patients whose respiratory specimens were positive for M. fortuitum between January 2003 and December 2005. Among 182 patients whose specimens were positive for M. fortuitum, 26 were positive at least twice. We retrospectively reviewed their characteristics, and clinical courses.

Of the 26 patients, 15 had two positive culture results for M. fortuitum; the other 11 had three or more. Sixteen patients were male and the median age was 61.5 years. Major presenting symptoms were cough (65%) and sputum (58%). Most patients had known underlying lung diseases, including prior tuberculosis (54%), lung cancer (15%), idiopathic pulmonary fibrosis (15%), and other mycobacterial lung disease (15%). The most common CT findings were bronchiectasis (80%). Only one patient received specific prolonged antibiotic therapy against M. fortuitum infection; the other 25 did not. No patients showed clinical aggravation during the follow-up period, although in five patients their underlying lung diseases continued to progress. The median follow-up duration was 12.5 months and none of the patients whose sputum specimens were available had persistent positive cultures for M. fortuitum.

M. fortuitum usually causes colonization or transient infection in patients with underlying lung disease, such as prior tuberculosis or bronchiectasis. The majority of patients may not need to receive prolonged antibiotic therapy for M. fortuitum isolates.