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In settings with high contamination of MGIT cultures, the performance of the Capilia test is diminished.

Background & objectives: Early case detection is essential to interrupt transmission and to prevent further spread of tuberculosis (TB) in high endemic settings. Nucleic acid amplification tests (NAATs) with visual read-outs are ideal as point-of-care tests. Truenat™ MTB is an indigenous chip-based NAAT for detection of Mycobacterium tuberculosis , which involves extraction of DNA and real-time polymerase chain reaction (PCR) using portable, automated, battery-operated instruments. The current multicentric study was aimed to evaluate Truenat for detection of MTB in sputum samples obtained from patients with presumptive pulmonary TB with reference to culture as gold standard and Xpert as a comparator. Methods: The study was conducted at four sites, namely ICMR-National Institute for Research in Tuberculosis, Chennai; All India Institute of Medical Sciences, New Delhi; ICMR-National JALMA Institute for Leprosy and Other Mycobacterial Diseases, Agra; and National Institute of TB and Respiratory Diseases, New Delhi. Patients suspected to have TB were screened for eligibility. Two sputum samples were collected from each patient. Tests included smear, Xpert and Truenat directly from the sputum sample and culture by Lowenstein-Jensen (L-J) medium and MGIT960 from decontaminated pellets. Sample used for Truenat assay was coded. Resolution of Truenat false positives was done using an in-house PCR with TRC 4 primers. Results: The study enrolled 2419 presumptive TB patients after screening 2465 patients, and 3541 sputum samples were collected from the enrolled patients. Results of 2623 samples were available for analysis. Truenat showed a positivity rate of 48.5 per cent as compared to 37.0 per cent by Xpert. The sensitivities of Truenat and Xpert were was 88.3 and 79.7 per cent, respectively in comparison with culture. Interpretation & conclusions: Truenat MTB identified more positives among culture-confirmed samples than Xpert and had higher sensitivity. In addition, other advantageous operational features of Truenat MTB were identified which would be useful in field settings.

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Diagnosis of latent tuberculosis infection is a myth for want of a simple, direct tool. Simulation of hypoxic environment was done to create a novel hypothetical model for persistence using processed sputum samples. The adaptation of tubercle bacilli to hypoxic environment seems to be influenced by pre-existing clinical status of the patients at the time of sputum collection, resulting in varied growth pattern. Bacilli from 36 samples did not get adapted to latency of which 15 samples were from patients in whom the disease was well established and the tubercle bacilli in them probably did not experience any stress whatsoever. Similarly, 10 of the 37 samples showing the presence of cultivable cells in both aerobic and anaerobic conditions were from patients who had relapsed. The bacilli in these samples had been probably experiencing stress and thus were ready to adapt to the hypoxic environment. Diagnostic luciferase reporter phage assay for non-replicating persistors (DLRPA-NRP) identified 30 additional positives which failed to grow on Lowenstein-Jensen medium. Presence of viable bacilli in these samples was confirmed by reverse transcriptase-PCR (RT-PCR) for 16S rRNA indicating either the improved sensitivity of the assay to detect actively growing bacilli or its ability to detect non-replicating persistors. The utility of LRP assay to detect both dormant and active tubercle bacilli was explored in this work and was optimized using lysis inhibition to diagnose tuberculosis with rapidity, improved sensitivity and specificity. DLRPA-NRP, a rapid growth based assay is thus developed to detect both dormant and actively growing tubercle bacilli.