Challenges, innovations and considerations for the use of tongue swabs in Mycobacterium tuberculosis complex detection

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Abstract Background Sputum-based testing has long been the cornerstone of tuberculosis (TB) diagnosis, but emerging specimen types like tongue swabs (TS) offer additional approaches for detecting Mycobacterium tuberculosis complex (MTBC). This two-phase study evaluated the impact of storage and transport conditions, along with laboratory processing modifications, to improve MTBC detection using TS tested on quantitative PCR (qPCR) and Xpert MTB/RIF Ultra (Ultra). Methods Participants with positive Ultra sputum were enrolled at a healthcare facility in Johannesburg, South Africa. In Phase one, five serial TS were collected per participant and transported “dry” at 2-8°C. In Phase two, seven TS were collected and stored “dry,” in Tris-EDTA (TE) buffer or PrimeStore® Molecular Transport Medium (MTM) and subjected to different storage temperatures (−80°C or 37°C) before laboratory testing. Results Results using qPCR and Ultra demonstrated that MTBC detection from serially collected TS was possible but sporadic, particularly in individuals with lower bacillary loads. Vortex bead beating (VBB) improved detection compared to heat lysis alone. Storage at −80°C was shown to be a viable option for longer term storage while short-term storage at 37°C was feasible. Ultra testing showed improved detection when TS were processed with diluted SR buffer. Conclusions TS offer a viable, though variable, specimen type for MTBC detection. Optimizing processing methods, such as incorporating VBB and diluted SR buffer, and selecting appropriate storage conditions can enhance diagnostic performance and support broader implementation in diverse settings.

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