Diagnostic accuracy and usability of the Pluslife MTB assay on tongue and sputum swabs in symptomatic and asymptomatic adults in South Africa

Abstract

Abstract Background Access to accurate tuberculosis (TB) diagnostics remains limited, particularly in high-burden settings. The Pluslife MTB assay is among the first molecular tests specifically designed for swab-based detection of Mycobacterium tuberculosis complex (MTBC) and offers near point-of-care use. Methods We conducted a prospective diagnostic accuracy study in South Africa to evaluate the performance of the Pluslife assay on tongue swabs (TSs) and sputum swabs (SSs) among symptomatic and asymptomatic adults. Results were compared against liquid culture as the reference standard and Xpert MTB/RIF Ultra (Xpert Ultra) as a comparator. Operational characteristics and ease-of-use were assessed through structured observation and Likert-scale scoring by testing personnel. Results Of 256 participants enrolled, 92 [36%] were people with HIV (PHIV) and 217 were included in the final analysis. Culture confirmed TB in 41/217 (19%). The Pluslife assay demonstrated sensitivity of 85% (95% CI: 70.8-94.4) on SSs, comparable to Xpert Ultra on sputum (83%, 95% CI: 67.9-92.8), and detected one additional case missed by Xpert Ultra. Sensitivity on TSs was lower (63%, 95% CI: 46.9-77.9), particularly among PHIV. Specificity exceeded 97% across specimen types. Concordance on TSs between Pluslife and Xpert Ultra increased with higher bacterial loads. Operational evaluation showed short hands-on time and high ease-of-use scores, though limitations were noted for patient identifier recording and troubleshooting on the Pluslife MiniDock device. Conclusions The Pluslife MTB assay on SSs shows comparable performance to existing rapid diagnostics and favorable usability. Tongue swabs remain feasible but less reliable, supporting sputum as the preferred first specimen for TB diagnosis. Summary The Pluslife MTB assay showed high diagnostic accuracy on sputum swabs, comparable to Xpert Ultra, with high specificity and acceptable usability. Performance on tongue swabs was lower, particularly among PHIV, supporting sputum as the preferred first specimen for TB diagnosis.