Tongue swab Xpert MTB/RIF Ultra for tuberculosis diagnosis in Ethiopian prisons

Tuberculosis (TB) diagnosis remains a major challenge in Ethiopian prisons, where access to diagnostics is limited. Current TB diagnostic strategies in Ethiopian prisons rely primarily on sputum-based testing. However, sputum collection is often challenging due to logistical barriers and infection-control concerns. Tongue swabs offer a promising non-sputum alternative. We assessed the diagnostic accuracy and feasibility of tongue swab testing using Xpert MTB/RIF Ultra (Ultra) for diagnosing pulmonary TB in Ethiopian prisons. Incarcerated men (≥18 years) presenting with a cough of any duration were enrolled. Two tongue swabs were collected from each participant: an early-morning swab and a second swab collected 30 min later. Tongue swabs were processed using a 2:1 sample reagent (SR) to sample ratio and tested with Ultra. Diagnostic accuracy was assessed against a composite microbiological reference standard (MRS) comprising sputum Ultra and liquid culture. Of 221 participants included in the final analysis, 34 (15.4%) had TB. Compared with the MRS, tongue swab Ultra detected 21 cases, yielding a sensitivity of 61.8% (95% CI: 44.7%–76.6%) and a specificity of 100.0%. Sensitivity compared with sputum Ultra was 63.6% (95% CI: 45.1%–79.6%), with 100.0% specificity. Sensitivity varied according to sputum Ultra bacillary load: 100.0% (9/9) for medium or high loads, 70.6% (12/17) for low or very low loads, and 0.0% (0/7) for “trace” loads. Tongue swab testing with Ultra was feasible and showed modest sensitivity but excellent specificity for TB diagnosis in Ethiopian prisons, supporting its use as a complementary diagnostic approach to improve case detection.

IMPORTANCE

This study is among the few to evaluate tongue swab testing using Ultra for TB diagnosis in a sub-Saharan African prison setting. It demonstrates the diagnostic performance and operational feasibility of this approach in a high-burden prison context. It supports the potential integration of non-sputum-based diagnostic approaches into prison TB diagnostic systems. Tongue swab testing using Ultra could improve access to TB diagnostics within existing case-finding algorithms, particularly by identifying individuals who are unable or unwilling to produce sputum.