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Review 2: "Tongue Swab Testing on Two Automated Tuberculosis Diagnostic Platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima"

The reviewers found the methods rigorous, and with conclusions and interpretations supported by their results. Reviewers did comment that additional detail in describing their methods, such as by following established guidelines, would offer additional clarity.

Published onNov 14, 2023
Review 2: "Tongue Swab Testing on Two Automated Tuberculosis Diagnostic Platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima"
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key-enterThis Pub is a Review of
Tongue swab testing on two automated tuberculosis diagnostic platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima
Tongue swab testing on two automated tuberculosis diagnostic platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima

ABSTRACT Tongue dorsum swabbing is a potential alternative to sputum collection for tuberculosis (TB) testing. Previous studies showed that Cepheid Xpert® MTB/RIF Ultra (Xpert Ultra) can detect Mycobacterium tuberculosis (MTB) DNA in tongue swabs stored in buffer, with 72% sensitivity and 100% specificity relative to a sputum microbiological reference standard (sputum MRS). The present study evaluated a more convenient sample collection protocol (dry swab storage), combined with streamlined sample processing protocols, for side-by-side analysis using two commercial TB diagnostic tests: Xpert Ultra and Molbio Truenat® MTB Ultima (MTB Ultima). Copan FLOQSwabs were self-collected, or collected by study workers, from 321 participants in Western Cape, South Africa. All participants had symptoms suggestive of TB, and 245 of them had sputum MRS-confirmed TB (by sputum culture and/or Xpert Ultra). One tongue swab per participant was tested on Xpert Ultra and another tongue swab was tested with MTB Ultima. Xpert Ultra was 75.4% sensitive and 100% specific, and MTB Ultima was 71.6% sensitive and 96.9% specific, relative to sputum MRS. When sample lysates that were false-negative by MTB Ultima were frozen, thawed, and re-tested, MTB Ultima sensitivity rose to 79.1%. Both tests were more sensitive with swabs from participants with higher sputum Xpert semi-quantitative results. The protocol for Xpert Ultra enabled fast and easy testing of dry-stored swabs with no loss of accuracy relative to previous methods. MTB Ultima testing of dry-stored swabs exhibited comparable performance to Xpert Ultra. These results further support tongue swabs as easy-to-collect samples for high-throughput TB testing.

RR:C19 Evidence Scale rating by reviewer:

  • Reliable. The main study claims are generally justified by its methods and data. The results and conclusions are likely to be similar to the hypothetical ideal study. There are some minor caveats or limitations, but they would/do not change the major claims of the study. The study provides sufficient strength of evidence on its own that its main claims should be considered actionable, with some room for future revision.



The manuscript under review describes novel protocols for tongue swab processing for subsequent molecular MTB detection and provide clinical evidence for their performance. The current study adds to the growing body of evidence supporting the feasibility and value of tongue swabs for TB detection, which is encouraging given the pressing need for alternative, non-sputum sample types for TB detection; reporting needs to be improved, though. 

Despite the fact that this is a diagnostic accuracy study, the STARD guidelines are not followed. The purpose of the STARD (Standards for Reporting of Diagnostic Accuracy Studies) guideline is to improve the transparency and completeness of diagnostic accuracy study reports: . Therefore, when summarizing the findings of research on diagnostic accuracy, it is critical to follow this guideline. The authors' findings are highly valuable to the field and should be published, but it would be helpful if they could enhance the reporting quality in accordance with the guidelines in their manuscript. This is something they could easily accomplish during a round of revisions. Please re-structure the manuscript in accordance with the guidelines to ensure high-quality reporting.

Section: Title

  1. According to the STARD guidelines, studies on diagnostic accuracy should be clearly identified in the title. Because the current title does not allude to the study design, I would advise heeding this recommendation.

Section: Abstract

  1. Provide 95% confidence intervals for the accuracy estimates.

  2. If the study protocol was registered, include the registration number and name of the registry.

  3. Line 26-28: Please clearly state if fresh or frozen samples were used.

  4. Line 35: It is unclear how the authors conclude that tongue swab testing is appropriate for high-throughput TB testing based on their findings, considering that low-throughput systems like Xpert Ultra and MTB Ultima were used in the study.

Section: Introduction

  1. Line 41-42: For readers who are unfamiliar with the field, please provide more details on why a different sample type than sputum is desired for TB testing.

  2. Line 56-57: Please provide references.

  3. Line 66-77: It seems like the content would be better suited for discussion than introduction. To clearly identify the study objectives, I suggest rephrasing part of the content.

Section: Methods

  1. Line 88-100: Please elaborate on the eligibility criteria for each cohort.

  2. Please provide details on the reference standard and the reasoning behind its selection.

  3. It is not stated how the sample size for each cohort was determined.

  4. It is unclear how the indeterminate/invalid results were handled.

Section: Results

  1. Line 169-170: Please provide a clear explanation for why nine participants were excluded from the analysis. You note on Line 172 that some participants were excluded from the analysis because of incomplete sample collection, but it is not clear if this applies to all nine participants who were excluded.

  2. Please provide 95% confidence intervals for the accuracy estimates.

  3. Line 187-188: Please clearly state the number of indeterminate/invalid results per platform. Although lines 194 to 196 imply this, the numbers in this paragraph do not match the numbers in Table 2. In addition, line 170 states that 321 participants in total were included in the analysis, as opposed to the 320 stated here.

  4. Line 194: Please report on the commonly observed error types per platform.

Overall, the results of the study add to the body of evidence in favor of using tongue swabs in place of sputum collection in situations where it is not feasible. Their use has the potential to improve access to TB testing and lower occupational risks for healthcare professionals. 

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