Diagnostic usefulness of the GenoType MTBDRplus assay for detecting drug-resistant tuberculosis using AFB smear-negative specimens with positive TB-PCR result

Abstract

Background The aim of this study was to evaluate the diagnostic accuracy of the GenoType MTBDRplus assay in detecting drug-resistant tuberculosis (DR-TB) by using acid-fast bacilli (AFB) smear-negative specimens with positive TB-PCR results. Methods The MTBDRplus assay was performed with 2 different categories of 117 samples, including AFB smear-positive specimens (n = 53) and AFB smear-negative specimens (n = 64), which exhibited positive TB-PCR results, at a single institution. The results were retrospectively compared with the results of the phenotypic drug susceptibility test (DST), for reference. Results A total of 105 tests were finally analyzed. Of these, 54 tests were conducted using AFB smear-negative specimens with positive TB-PCR results. The MTBDRplus assay for these 54 samples demonstrated a sensitivity of 100%, specificity of 98%, positive predictive value (PPV) of 75%, and negative predictive value (NPV) of 100% in detecting rifampicin resistance. With these same species, the sensitivity, specificity, PPV, and NPV values for the MTBDRplus assay were 83.3%, 97.9%, 83.3%, and 97.9%, respectively, for the detection of isoniazid resistance. The overall correlation between the MTBDRplus assay and phenotypic DST demonstrated excellent agreement for detection of rifampicin resistance (κ = 0.847) and for detection of INH resistance (κ = 0.812), respectively. Conclusions The MTBDRplus assay can be used effectively even on AFB smear-negative specimens from TB patients, when the TB-PCR is positive. This result might help clinicians to manage patients with suspected DR-TB in difficult situations.

Keywords:

• Mycobacterium tuberculosis
• MTBDRplus
• AFB smear-negative specimen

Acknowledgments

The authors thank Ms Sarah Chang for her help in data collection.

Disclosure statement

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.