Rapid discrimination between Mycobacterium tuberculosis (MTB) and nontuberculous mycobacteria (NTM) is critical for patient treatment and to avoid unnecessary expenditure on infection control. Because real-time PCR assays distinguish MTB from NTM, we evaluated the performance of two real-time PCR assays (AdvanSure and PowerChek).Methods
This study used 143 DNA samples from respiratory specimens which were collected based on routine PCR results using Anyplex kit. A total of 87 positive samples (65 MTB and 22 NTM) and 56 negative samples were collected consecutively during 6 months and 1 month, respectively. The diagnostic performance of PCR assays (AdvanSure and PowerChek) was retrospectively analyzed based on the results of conventional mycobacterial tests and routine PCR assay.Results
Based on culture results, the sensitivities/specificities of AdvanSure and PowerChek were 90.7%/87.6% and 92.6%/85.4%, respectively, for MTB detection. For PCR-positive specimens, the quantification cycle (Cq) values of smear-negative specimens were higher than those of the smear-positive specimens (P < 0.001). As expected, the two PCR assays had the same sensitivities for NTM detection, viz. 90.0%, and their specificities were 99.2% and 98.4%, respectively. The overall agreement rate between the three PCR assays was 96.5% for MTB and 97.9% for NTM.Conclusion
The sensitivities of PCR assays in our study might be overestimated, because this study enrolled relatively lower number of PCR-negative samples which potentially missed PCR-negative but culture-positive specimens. However, the two real-time PCR assays for detecting MTB and NTM perform equally well in relative performance evaluation and their Cq values can be considered suitable for predicting smear-positive specimens.