Oral swab test finds many TB cases in Ethiopian prisons

Tuberculosis remains a hidden threat in crowded, high‑burden places such as prisons, where many people with active disease are undiagnosed. Asymptomatic or subclinical TB — infections that cause little or no cough — is increasingly recognized and makes screening harder when tests rely on sputum. In response to this challenge, a team led by Kelemework Adane explored a sputum‑free approach: oral swab analysis (OSA) paired with the molecular test Xpert MTB/RIF Ultra (Ultra). The study was a cross‑sectional evaluation set in Ethiopian carceral settings, aimed at assessing whether an easy, non‑invasive oral swab could help diagnose pulmonary TB among incarcerated adults. The researchers enrolled incarcerated adults (≥18 years) presenting with a cough of any duration, collected oral swab samples, and processed them using a customized 2:1 sample-to-reagent protocol before running Ultra. The work tests whether OSA with Ultra can perform well enough to be useful for routine screening in prisons, where sputum-free options could reach people who cannot produce sputum or who have minimal symptoms.

The study screened 858 incarcerated men across two prisons and one detention center; 240 met eligibility criteria and 221 were included in the final analysis. The team used a composite microbiological reference standard (MRS) made up of sputum Ultra and liquid culture to define pulmonary TB. By that standard, 34 participants (15.4%) had TB. Oral swab Ultra detected 21 of those cases, giving a sensitivity of 61.8% (95% CI, 44.7–76.6%) and a specificity of 100% compared with the composite MRS. When compared specifically to sputum Ultra, oral swab sensitivity was 63.6% (95% CI, 45.1–79.6%) with 100% specificity. Performance depended on bacillary load: oral swabs detected all participants with medium or high sputum bacillary loads, but failed to detect any of seven cases with trace sputum bacillary loads. The tests were performed using the customized 2:1 sample-to-reagent protocol for oral swabs followed by Xpert MTB/RIF Ultra.

These results suggest that oral swab testing with Xpert MTB/RIF Ultra, using a tailored processing protocol, is a feasible and promising complement to sputum‑based diagnosis in prison settings. The test showed moderate‑to‑high sensitivity overall and perfect specificity in this study, and it reliably identified cases with higher bacillary burden. That pattern means oral swabs could pick up many of the infectious cases that contribute to ongoing transmission, while cases with very low bacillary load may still be missed. In practical terms, a non‑invasive oral swab option could expand screening reach to incarcerated people who cannot produce sputum or who have minimal symptoms, and it could be integrated into prison TB screening initiatives where rapid molecular testing like Xpert MTB/RIF Ultra is available. The authors present oral swab Ultra not as a replacement for sputum testing but as a complementary tool that can help find additional TB cases in high‑burden carceral environments such as those studied in Ethiopia.