Tongue swabs show promise for tuberculosis detection

Sputum testing has been the long-standing standard for diagnosing tuberculosis, but researchers are exploring new specimen types to expand how the disease is detected. In a study led by corresponding author Anura David, investigators tested whether tongue swabs (TS) could be a practical alternative or complement to sputum for identifying Mycobacterium tuberculosis complex (MTBC). The work was organized as a two-phase study at a healthcare facility in Johannesburg, South Africa. The team wanted to know how different transport and storage conditions, together with laboratory processing choices, would affect the ability to find MTBC on TS when using common molecular tests. Specifically, the study compared quantitative PCR (qPCR) and the Xpert MTB/RIF Ultra test (referred to as Ultra) as readouts for MTBC presence. By collecting multiple TS from each participant and changing variables such as whether swabs were kept dry or placed in buffer, and whether samples were stored cold or warm before testing, the researchers sought practical guidance on whether TS could reliably be used for TB detection and what steps would make them more effective in routine practice.

The study enrolled people who had already tested positive on Ultra using sputum. In Phase one, five serial tongue swabs were taken from each participant and transported “dry” at 2–8°C to the laboratory. Phase two expanded the experiment: seven TS were collected from participants and stored either “dry,” in Tris-EDTA (TE) buffer, or in PrimeStore® Molecular Transport Medium (MTM). Those samples were then subjected to different storage temperatures, including −80°C for longer-term preservation and 37°C to simulate short-term warm conditions, before laboratory testing. Results read by qPCR and Ultra showed MTBC could be detected from serial TS, but detection was sporadic, especially in individuals with lower bacillary loads. A laboratory processing step called 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 also showed improved detection when TS were processed with diluted SR buffer.

Taken together, these findings suggest that tongue swabs can serve as a viable, if variable, specimen type for detecting MTBC when paired with molecular tests like qPCR and Ultra. The variability emphasizes that technique and handling matter: incorporating vortex bead beating (VBB) into laboratory workflows and using diluted SR buffer when running Ultra increased the chances of finding MTBC on swabs. The study also identifies practical storage options—using −80°C for longer-term archiving and recognizing that short-term 37°C storage is possible—which can inform how programs collect and transport TS in different settings. By highlighting which combinations of storage and processing improve detection, the work offers a roadmap for labs and health programs considering tongue swabs as a supplement to sputum testing. With further validation and operational adjustments, TS collection paired with the identified methods could expand diagnostic options and adapt TB testing to a wider range of clinical and field environments.