Clinical Significance of Mycobacterium avium Complex Isolates at a Medical Center in Northern Taiwan

Abstract

We read with great interest the case report by Shen et al1 in the July 2010 issue of Journal of the Formosan Medical Association. In that retrospective study, the authors described the clinical significance of Mycobacterium avium complex (MAC) that had been isolated from respiratory specimens at a medical center in southern Taiwan. We wonder whether similar findings could be noted in other parts of Taiwan. Therefore, we would like to report our observation about nontuberculous mycobacteria (NTM) in northern Taiwan. From January to December 2009, a total of 1,756 specimens from 898 patients positive for NTM were identified at the Mycobacteriology Laboratory at the National Taiwan University Hospital, a 2,500-bed tertiary care center in northern Taiwan that receives more than 6,000 daily clinical visits. The most common NTM isolates identified were MAC (579 isolates from 279 patients), followed by Mycobacterium abcesssus (275 isolates from 174 patients), and Mycobacterium fortuitum (258 isolates from 186 patients). Among the 279 patients from whom MAC was isolated, MAC colonization was noted in 210 (75.3%) patients, and MAC caused NTM disease in 69 (24.7%) patients, based on the 2007 criteria of the American Thoracic Society/Infectious Diseases Society of America.2 Those findings were consistent with those from our previous study conducted during the period January 2000 to December 2008 at the same institution.3 In that study, a total of 9,204 NTM isolates were recovered from 4,786 patients, and 2,761 isolates from 1,515 patients were confirmed to be MAC. Among those patients, MAC colonization was noted in 1,282 (84.6%) and MAC caused NTM diseases in 233 (15.4%). The annual prevalence of MAC colonization ranged from 80.0% (2000) to 87.4% (2006). These findings are consistent with those reported by Shen et al,1 namely that only 12 (22.2%) of 54 patients with positive MAC isolates had clinically significant MAC pulmonary disease. In addition, trend analysis has revealed that the annual incidence (per 100,000 inpatients and outpatients) of MAC colonization increased