Diagnostic value of the strand displacement amplification method compared to those of Roche Amplicor PCR and culture for detecting mycobacteria in sputum samples

We compared the ability of the semiautomated BDProbeTec-SDA system, which uses the strand displacement amplification (SDA) method, with that of the Recite Amplicor-PCR system and the Septi-Chek AFB culture system to directly detect Mycobacterium tuberculosis complex (MTB) and other mycobacteria in sputum samples. A total of 530 sputum samples from 299 patients were examined in this study. Of the 530 samples, 129 were culture positive for acid-fast bacilli with the Septi-Chek AFB system; 95 for MTB, 29 for,ll. avium-M. intracellulare complex (MAC), and 5 for other mycobacteria. The BDProbeTec-SDA system detected 90 of the 95 samples culture positive for MTB (sensitivity, 94.7%), and the Amplicor-PCR system detected 85 of the 95 samples culture positive for RITE (sensitivity, 89.5%). The specificity of each system, based on the clinical diagnosis, was 99.8% for SDA and 100% for PCR, respectively. Among the 29 samples culture positive for ILIAC, the BDProbeTec-SDA system detected MAC in 24 samples (sensitivity, 82.8%), whereas the Amplicor-PCR system detected MAC in 24 samples (sensitivity, 79.3%). The specificities of the systems were 98.3 and 100%, respectively. The high degrees of sensitivity and specificity of the BDProbeTec-SDA system suggest that it should be very useful in clinical laboratories for the rapid detection of mycobacteria in sputum samples.