Rapid diagnosis of Mycobacterium tuberculosis with Truenat MTB: a near-care approach

Abstract

Background: Control of the global Tuberculosis (TB) burden is hindered by the lack of a simple and effective diagnostic test that can be utilized in resource-limited settings.

Methods: We evaluated the performance of Truenat MTB™, a chip-based nucleic acid amplification test in the detection of Mycobacterium tuberculosis (MTB) in clinical sputum specimens from 226 patients with suspected pulmonary tuberculosis (TB). The test involved sputum processing using Trueprep-MAG™ (nanoparticle-based protocol run on a battery-operated device) and real-time PCR performed on the Truelab Uno™ analyzer (handheld, battery-operated thermal cycler). Specimens were also examined for presence of MTB using smear microscopy, liquid culture and an in-house nested PCR protocol. Results were assessed in comparison to a composite reference standard (CRS) consisting of smear and culture results, clinical treatment and follow-up, and radiology findings.

Results: Based on the CRS, 191 patients had "Clinical-TB" (Definite and Probable-TB). Of which 154 patients are already on treatment, and 37 were treatment naïve cases. Remaining 35 were confirmed "Non-TB" cases which are treatment naïve cases. The Truenat MTB test was found to have sensitivity and specificity of 91.1% (CI: 86.1-94.7) and 100% (CI: 90.0-100) respectively, in comparison to 90.58% (CI: 85.5-94.3) and 91.43% (CI: 76.9-98.2) respectively for the in-house nested PCR protocol.

Conclusion: This preliminary study shows that the Truenat MTB test allows detection of TB in approximately one hour and can be utilized in near-care settings to provide quick and accurate diagnosis.

Figure 1. Study design for evaluation of Truenat MTB performance.

Figure 2. Sample loading on Trueprep-MAG device.

Figure 3. Addition of 5 µl of DNA to Truenat MTB chip.

Figure 4. Enlistment and outcome of study.

Figure 5. Forest plot for sensitivity values of microbiological and molecular methods.

Forest Plot for sensitivity of smear, Culture, Nested and Truenat molecular methods with pooled sensitivity. Performance of molecular methods studies reporting sensitivity. Point estimates of sensitivity estimates from each study are shown as solid circles. Solid lines represent the 95%CI. CI = confidence interval.

Figure 6. ROC curves for various techniques evaluated in this study.

Performance of molecular tests reporting sensitivity and specificity. The curve is the regression line that summarises the overall diagnostic accuracy. Q* is an index defined by the point on the SROC curve where the sensitivity and specificity are equal, which is the point closest to the top-left corner of the ROC space. SROC: summary receiver operating curve; AUC: area under the curve; SE (AUC): standard error of AUC; SE (Q*): standard error of Q* index.