Avalilação PREreview de High Sensitivity of the BioNote Anigen™ Rapid Rabies Antigen Test in Detection of Diverse Rabies Virus Variants Suggests Utility for Global Rabies Control

Summary

This preprint evaluates the performance of the Xpert MTB/XDR assay for rapid detection of drug resistance in Mycobacterium tuberculosis (Mtb) beyond rifampicin, specifically targeting fluoroquinolone and aminoglycoside resistance. The authors compiled a multi-site panel of clinical specimens across multiple geographic regions and compared Xpert MTB/XDR results against conventional phenotypic drug-susceptibility testing (DST). The study reports high sensitivity and specificity for several resistance-associated markers, suggesting that this assay could substantially reduce time to diagnosis of multidrug-resistant (MDR) and extensively drug-resistant (XDR) tuberculosis and enable more rapid treatment decisions. The preprint highlights the importance of expanding rapid molecular diagnostics beyond rifampicin resistance alone, particularly given rising global rates of second-line drug resistance. The authors argue that Xpert MTB/XDR could serve as a practical, near–near-point-of-care diagnostic tool, especially in decentralized and resource-limited settings.

Major Concerns

• Unclear specimen types and clinical relevance

  • The manuscript does not clearly state whether the tested samples were cultured isolates, direct patient specimens (e.g., sputum), or a mixture of both.

  • Actionable suggestion: The authors should explicitly specify, for each sample (or sample group), whether it was a cultured isolate or a direct clinical specimen. If direct specimens were used, details should be provided on smear status (smear-positive vs. smear-negative), specimen type (sputum, extrapulmonary), and any preprocessing steps.

  • If the panel is enriched for resistant isolates, this should be clearly acknowledged.

  • Actionable suggestion: The authors should report the proportion of resistant vs. susceptible samples and discuss how enrichment may affect positive and negative predictive values in routine clinical populations.

• Limited description of geographic and epidemiological diversity

  • While the study includes samples from multiple sites, there is insufficient detail about the diversity of Mtb lineages, resistance-conferring mutations, and patient backgrounds.

  • Actionable suggestion: The authors should include a table or supplementary material describing, for each specimen or site: Geographic origin, Mtb lineage, Specific resistance-associated mutations detected, and Prior treatment status (new case vs. previously treated)

  • This information is necessary for readers to assess how generalizable the results are to different global TB settings.

• Performance in low bacterial load and heteroresistance not addressed

  • The manuscript does not evaluate or discuss assay performance in cases of low bacterial burden or heteroresistance (mixed susceptible and resistant populations), which are common in smear-negative, extrapulmonary, or early TB.

  • Actionable suggestion: The authors should either:

    • Present stratified performance data by smear status or bacterial load (if available), or

    • Explicitly state that such data were not collected and discuss this as a limitation.

  • Additionally, discussion of heteroresistance detection (or lack thereof) should be included, along with implications for missed resistance.

• Lack of information on limits of detection and sample processing

  • No data are provided on the assay’s limit of detection (LOD) or the impact of sample quality and processing on assay performance.

  • Actionable suggestion: The authors should report any available LOD data or reference existing validation studies. They should also describe sample processing protocols (e.g., decontamination methods) and discuss how these may influence sensitivity in real-world settings.

Minor Concerns

• Terminology and definitions

  • Terms such as “non-rifampicin drug resistance,” “MDR,” and “XDR” are used without a clear definition.

  • Actionable suggestion: The authors should define all resistance categories according to current WHO guidelines and clarify whether resistance refers to mono-resistance, multidrug resistance, or resistance across multiple drug classes.

• Clinical interpretation and limitations

  • The discussion does not sufficiently address clinical contexts in which molecular assays may underperform or mislead.

  • Actionable suggestion: The authors should expand the discussion to explicitly address: Paucibacillary and extrapulmonary disease, Heteroresistance, Discordance between molecular resistance markers and phenotypic DST

  • They should also comment on the potential risk of overdiagnosis or overtreatment when molecular resistance detection does not correlate with phenotypic resistance, and suggest confirmatory testing strategies or follow-up studies.

Competing interests

The author declares that they have no competing interests.

Use of Artificial Intelligence (AI)

The author declares that they used generative AI to come up with new ideas for their review.