Detecting Mycobacterium Tuberculosis in BACTEC MGIT 960 Cultures by COBAS AMPLICOR MTB in Routine Clinical Practice

Introduction: The rapid, automated cultivation and detection system, BACTEC MGIT 960, is widely used in Taiwan. But the high nontuberculous mycobacteria (NTM) isolation rate is a concern that should be carefully evaluated. The aim of this study was to evaluate the ability of the commercial COBAS AMPLICOR MTB amplification system to identify Mycobacterium tuberculosis (M. tuberculosis) in positive BACTEC MGIT 960 cultures in routine clinical practice. Methods: We tested 270 positive BACTEC MGIT 960 cultures with the COBAS AMPLICOR MTB at Taipei Medical University-Wan Fang Hospital from March 1, 2006 through February 28, 2007. The COBAS AMPLICOR MTB results were compared with mycobacterial species identification by conventional biochemical testing. Results: We found that 207 (76.7%) COBAS AMPLICOR MTB results were regarded as conclusive, and 63 (3 M. tuberculosis, 60 NTM) inconclusive. Among 176 conclusive results positive for M. tuberculosis, 174 were regarded as true positive and 2 false positive. Among 31 conclusive results negative for M. tuberculosis, 30 were regarded as true negative and 1 false negative. After excluding the inconclusive results, we further found that the sensitivity, specificity, and positive/negative predictive values of the COBAS AMPLICOR MTB test were 99, 94, 99, and 97%, respectively. Conclusion: COBAS AMPLICOR MTB might be suitable for rapid detection and identification of M. tuberculosis in BACTEC MGIT 960 cultures in routine clinical practice.