Diagnostic accuracy of self-collected tongue swabs for Mycobacterium tuberculosis complex detection in individuals being assessed for tuberculosis in South Africa using the Xpert MTB/RIF Ultra assay.

Abstract

Objectives: Tongue swabs (TS) have shown potential for detecting Mycobacterium tuberculosis complex (MTBC) through downstream molecular testing. Analytical performance varies, depending on the processing protocol and the molecular test used. This study aimed to first investigate the ease of use of TS collection in addition to acceptability by individuals being assessed for tuberculosis and second to determine the performance of self-collected TS on the Xpert MTB/rifampicin (RIF) Ultra (Ultra) assay (Cepheid, Sunnyvale, CA, USA) for MTBC and RIF resistance detection.

Methods: The ease of use of TS collection and acceptability by study participants was assessed through completion of a survey questionnaire. Analytical performance of self-collected TS on the Ultra assay was determined by comparing results with a liquid culture reference result and with Ultra on sputum. Results were additionally stratified by HIV and smear status.

Results: Of the 399 survey respondents, all were happy with the TS collection procedure with minimal discomfort reported. Data analysis was performed on 321 specimens. The sensitivity of the Ultra TS assay for MTBC detection was 78.1% (95% CI, 66.0-87.5%), whereas the specificity was 100% (95% CI, 98.6-100%). Test performance was better in individuals with a higher bacillary load, with some variability. On HIV-positive individuals, TS performance is ∼30% lower than that on sputum but also slightly better than smear microscopy, whereas the performance of TS among HIV-negative individuals is similar to sputum (93% vs. 97%). For RIF resistance profiling, the Ultra TS assay showed 41/41 (100%) concordance with phenotypic drug-susceptibility testing.

Discussion: Although self-collected TS have lower sensitivity compared with sputum, their ease of use and high acceptability make them a valuable additional specimen type for molecular tuberculosis testing. Self-collection can reduce the burden on healthcare workers and increase access to testing, particularly for individuals who are too busy to visit healthcare facilities or fear stigma.