Clinical significance of isolation of Mycobacterium avium complex from respiratory specimens

Background/Purpose: Mycobacterium avium complex (MAC) is frequently considered to be a contaminant or transient colonizer. To the best of our knowledge, there have been very few reports regarding the clinical significance of MAC isolates in respiratory specimens, and the associated disease spectrum in Taiwan. The purpose of this study was to investigate the clinical significance of MAC isolates in respiratory specimens. Methods: We retrospectively reviewed the medical records of patients in a medical center in Southern Taiwan from whom MAC isolates were recovered from respiratory specimens, and analyzed their clinical features, chest imaging findings, treatment and prognosis. We also performed an antibiotic susceptibility test on our MAC isolates. Results: The 64 isolates used in this study were recovered from April to October 2001 from respiratory specimens in 54 patients admitted to Kaohsiung Veterans General Hospital, Taiwan. According to the 2007 criteria of the American Thoracic Society, a total of 12 patients (22.2%) had clinically significant MAC pulmonary disease. Conclusion: Despite the increased frequency of recovering MAC from respiratory specimens, most cases did not meet the criteria of American Thoracic Society for clinically significant nontuberculous pulmonary disease. The minimum inhibitory concentrations of drugs against these MAC isolates might help to guide treatment, but further studies should be done.