Oral Swab Xpert MTB/RIF Ultra for Tuberculosis Diagnosis in Ethiopian Prisons

ABSTRACT As asymptomatic (subclinical) tuberculosis (TB) is increasingly recognized, there is a need for sputum-free diagnostic approaches applicable to both symptomatic individuals and population screening. Oral swab analysis (OSA) using Xpert MTB/RIF Ultra (Ultra) is a promising approach; however, its performance has not been evaluated in prisons. We conducted a cross-sectional study to assess the diagnostic accuracy of oral swab Ultra for TB diagnosis in Ethiopian prisons. Incarcerated adults (≥18 years) presenting with a cough of any duration were enrolled. Oral swabs were collected and processed using a customized 2:1 sample-to-reagent protocol and tested with Ultra. Diagnostic accuracy was evaluated against a composite microbiological reference standard (MRS) comprising sputum Ultra and liquid culture. Among 858 incarcerated men screened across two prisons and one detention center, 240 were eligible, and 221 were included in the analysis. Overall, 34 participants (15.4%) were diagnosed with pulmonary TB using MRS. Compared with the composite MRS, oral swab Ultra detected 21 cases, yielding a sensitivity of 61.8% (95% CI, 44.7–76.6%) and a specificity of 100%. Sensitivity compared with sputum Ultra was 63.6% (95% CI, 45.1–79.6%), with 100% specificity. Performance varied by bacillary burden: sensitivity reached 100% among participants with medium or high sputum bacillary loads, whereas none of the seven cases with trace bacillary loads were detected using oral swabs. In summary, oral swab Xpert Ultra, using a customized processing protocol, demonstrated moderate-to-high sensitivity for TB diagnosis in high-burden Ethiopian prisons, supporting its potential role as a complementary tool in prison TB screening initiatives. IMPORTANCE Prisons in high-burden countries such as Ethiopia remain heavily affected by undiagnosed tuberculosis (TB). Overreliance on sputum samples for diagnosis is a key contributing factor. Sputum-based tests may fail to capture all TB cases in such settings, as many incarcerated individuals with active TB are either unable to produce sputum or have asymptomatic (subclinical) disease. Patients with minimal or no symptoms (subclinical or asymptomatic TB), on the other hand, contribute to ongoing transmission. Oral swab analysis (OSA) using molecular diagnostics such as Xpert MTB/RIF Ultra (Ultra) offers a promising, non-invasive option for TB diagnosis. However, OSA with Ultra has not been systematically evaluated for TB screening in prison settings in high-burden regions, where diagnostic needs are greatest. In this study, we show that oral swab testing with Xpert Ultra is feasible and demonstrates moderate-to-high sensitivity for TB diagnosis in Ethiopian prisons.