Potential for the Use of Polymerase Chain Reaction (PCR) in the Detection and Identification of Mycobacterium tuberculosis Complex in Sputum Samples

The COBAS AMPLICOR Mycobacterium tuberculosis assay was evaluated for routine detection and identification of Mycobacterium tuberculosis complex (MTBC) in 629 sputum samples. In addition to the Polymerase Chain Reaction (PCR), diagnostic culture, which is considered the reference method, was also performed on theses samples. Of the 629 specimens tested, 64 were culture positive for M. tuberculosis and 51 were positive by COBAS AMPLICOR MTB assay and 19 specimens were considered PCR inhibitory. There were no false positive results in all tested samples and 3 PCR-negative, culture-positive specimens were considered false negative especially after reviewing the medical records for the 3 patients. A PCR inhibition rate of 3 % (19/629) was observed; these samples remained inhibitory despite re-testing. After excluding the inhibitory samples from the statistical analysis, the overall sensitivity, specificity, positive predictive value (PPV) and negative predictive values (NPV) for the COBAS AMPLICOR MTB assay were 94.4, 100, 100 and 99.5 % respectively compared to those of the diagnostic culture. In conclusion, the COBAS AMPLICOR PCR system proved itself a very useful component of today mycobacteriology laboratory.