Evaluation of a simplified IS6110 PCR for the rapid diagnosis of Mycobacterium tuberculosis in an area with high tuberculosis incidence

Purpose

To assess the diagnostic yield of a simplified IS6110-PCR in an area with high tuberculosis incidence.

Methods

Pulmonary (218) and extrapulmonary (121) samples were collected from 236 patients including smearpositive leprosy patients. All samples were processed to detect acidfast bacilli by microscopy, culture on solid media and PCR. To remove PCR inhibitors, three washing steps of the decontaminated pellet were included before mycobacterial cell lysis by heat treatment. No detergents, enzymes, or chelating agents were used. From the 339 samples, 34 were selected basing on their large volume and were tested by the commercial kit GenoType Mycobacteria Direct (GTMD) (VER 4, Hain Lifescience, Germany) in addition to the tests cited above.

Results

The overall sensitivity and specificity of PCR were 93.8 and 98.6% for pulmonary samples, 63.6 and 100% for extrapulmonary samples, respectively. The assay detected MTC in 94.2% of smear positive samples with a positive predictive value of 100%. No inhibition was found among seven samples that were PCR negative but bacteriological confirmed as containing Mycobacterium tuberculosis. No false positive result occurred with samples from leprosy patients. The sensitivities for PCR and GTMD were 81.8 and 75%, respectively.

Conclusion

PCR could efficiently complement conventional bacteriological tools for the rapid diagnosis of tuberculosis but cannot replace them.