Review 3: "Tongue Swab Testing on Two Automated Tuberculosis Diagnostic Platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima"

Soumitesh Chakravorty

doi:doi:10.1162/2e3983f5.f3955084

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.

by Soumitesh Chakravorty

Published onNov 14, 2023

Tongue swab testing on two automated tuberculosis diagnostic platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima

by Rachel C. Wood, Angelique K. Luabeya, Rane B. Dragovich, Alaina M. Olson, Katherine A. Lochner, Kris M. Weigel, Renée Codsi, Humphrey Mulenga, Margaretha de Vos, Mikashmi Kohli, Adam Penn-Nicholson, Mark Hatherill, and Gerard A. Cangelosi

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Published on Oct 11, 2023
www.medrxiv.org

Description

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:

Potentially informative. The main claims made are not strongly justified by the methods and data, but may yield some insight. The results and conclusions of the study may resemble those from the hypothetical ideal study, but there is substantial room for doubt. Decision-makers should consider this evidence only with a thorough understanding of its weaknesses, alongside other evidence and theory. Decision-makers should not consider this actionable, unless the weaknesses are clearly understood and there is other theory and evidence to further support it.

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Review:

This study provides a more convenient and user-friendly way of collecting tongue swab samples for molecular diagnostic testing to detect pulmonary tuberculosis. The authors verify the performance using two different commercial assays and claim equivalent performance to previous tongue swab collection methods with significantly lower sample handling time.

Overall the paper is well-written and a well performed clinical study. The conclusions drawn are valid with good justifications. I recommend the paper to be accepted if the authors can address the following comments:

The authors need to elaborate more in the discussion section on the potential effect of cold storage (-80C) on the results. No control condition experiments were done to show how the performance of the assay would be on freshly collected samples without storage, which is important for both the near-patient/point of care tests which the authors used to evaluate the sample collection method. This should be discussed as a limitation in the study.
The authors need to describe in more details, what the errors types were for invalid runs and whether sample collection and storage method may contribute to such errors
Line 161-162: Please mention that the Sample Reagent was not used in any step of sample processing, which is a key difference from what is recommended for sputum and most widely used for various off-label sample testing, and whether the authors believe that it may have any effect on the assay performance.
Line 171-172: Sample numbers add up to 221 and not 222

Review 3: "Tongue Swab Testing on Two Automated Tuberculosis Diagnostic Platforms, Cepheid Xpert® MTB/RIF Ultra and Molbio Truenat® MTB Ultima"

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