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. 2024 May 15;78(5):1313-1320.
doi: 10.1093/cid/ciae041.

New Manual Quantitative Polymerase Chain Reaction Assay Validated on Tongue Swabs Collected and Processed in Uganda Shows Sensitivity That Rivals Sputum-based Molecular Tuberculosis Diagnostics

Amy Steadman  1 , Alfred Andama  2   3 , Alexey Ball  1 , Job Mukwatamundu  3 , Khushboo Khimani  1 , Tessa Mochizuki  4 , Lucy Asege  3 , Alice Bukirwa  3 , John Baptist Kato  3 , David Katumba  3 , Esther Kisakye  3 , Wilson Mangeni  3 , Sandra Mwebe  3 , Martha Nakaye  3 , Irene Nassuna  3 , Justine Nyawere  3 , Annet Nakaweesa  3 , Catherine Cook  4 , Patrick Phillips  4 , Talemwa Nalugwa  3 , Christine M Bachman  1 , Fred Collins Semitala  2 , Bernhard H Weigl  1 , John Connelly  1 , William Worodria  2 , Adithya Cattamanchi  5
Affiliations

New Manual Quantitative Polymerase Chain Reaction Assay Validated on Tongue Swabs Collected and Processed in Uganda Shows Sensitivity That Rivals Sputum-based Molecular Tuberculosis Diagnostics

Amy Steadman et al. Clin Infect Dis. .

Abstract

Background: Sputum-based testing is a barrier to increasing access to molecular diagnostics for tuberculosis (TB). Many people with TB are unable to produce sputum, and sputum processing increases assay complexity and cost. Tongue swabs are emerging as an alternative to sputum, but performance limits are uncertain.

Methods: From June 2022 to July 2023, we enrolled 397 consecutive adults with cough >2 weeks at 2 health centers in Kampala, Uganda. We collected demographic and clinical information, sputum for TB testing (Xpert MTB/RIF Ultra and 2 liquid cultures), and tongue swabs for same-day quantitative polymerase chain reaction (qPCR) testing. We evaluated tongue swab qPCR diagnostic accuracy versus sputum TB test results, quantified TB targets per swab, assessed the impact of serial swabbing, and compared 2 swab types (Copan FLOQSWAB and Steripack spun polyester).

Results: Among 397 participants, 43.1% were female, median age was 33 years, 23.5% were diagnosed with human immunodeficiency virus, and 32.0% had confirmed TB. Sputum Xpert Ultra and tongue swab qPCR results were concordant for 98.2% (95% confidence interval [CI]: 96.2-99.1) of participants. Tongue swab qPCR sensitivity was 92.6% (95% CI: 86.5 to 96.0) and specificity was 99.1% (95% CI: 96.9 to 99.8) versus microbiological reference standard. A single tongue swab recovered a 7-log range of TB copies, with a decreasing recovery trend among 4 serial swabs. Swab types performed equivalently.

Conclusions: Tongue swabs are a promising alternative to sputum for molecular diagnosis of TB, with sensitivity approaching sputum-based molecular tests. Our results provide valuable insights for developing successful tongue swab-based TB diagnostics.

Keywords: diagnosis; nonsputum; oral swab; tongue swab; tuberculosis.

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Conflict of interest statement

Potential conflicts of interest. A. C. reports participation on the Medaica Advisory Board and stock or stock options for Medaica. All remaining authors: No reported conflicts of interest. All authors have submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest. Conflicts that the editors consider relevant to the content of the manuscript have been disclosed.

Figures

Figure 1.
Figure 1.
Measured mean log copies of Mycobacterium tuberculosis IS6110 per swab per participant by Xpert semiquantitative grade. Abbreviation: ns, not significant,
Figure 2.
Figure 2.
Quantity of MTB IS6110 copies present on 4 sequentially collected swabs. A, Heat map demonstrating decreasing recovery with each sequentially collected swab. B, Normalized MTB targets recovered from all swabs calculated as a percentage of the highest recovery condition (“100%”). C, Recovery of 4 swabs by Xpert semiquantitative status. Abbreviation: MTB, Mycobacterium tuberculosis.
Figure 3.
Figure 3.
Recovery of IS6110 copies from Copan versus Steripack swabs. A, Bland–Altman ratio of measured IS6110 copies recovered by Copan versus Steripack divided by log mean measured copies of IS6110. B, Measured log copies 1S6110 recovered from Steripack versus Copan.
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