Unmasking isoniazid resistance in rifampicin-susceptible TB: a national multicentre study using Xpert MTB/XDR

TB remains a major global health threat, worsened by drug resistance. Hr-TB (isoniazid resistance) in rifampicin-susceptible cases compromises outcomes. This study used Xpert MTB/XDR to determine Hr-TB prevalence and associated risk factors, informing national control strategies.A cross-sectional study was conducted in 74 Ethiopian health facilities (May-October 2024), including 841 rifampicin-susceptible TB cases. Hr-TB was evaluated using the Xpert MTB/XDR assay. Two-stage sampling and logistic regression estimated prevalence and identified significant predictors.The overall Hr-TB prevalence was 2.7%, higher among previously treated TB cases (16.2%) than in new TB cases (0.9%). Regional variation showed the highest prevalence in Gambella (7.1%), Oromia (6.2%), and Sidama (5.7%). Multivariable analysis identified prior TB treatment as the main predictor, including other previously treated cases (AOR = 138.48), relapses (AOR = 5.59), and history of treatment after failure (AOR = 45.51).Hr-TB remains a significant concern among rifampicin-susceptible TB patients in Ethiopia, particularly in previously treated cases, with regional variation underscoring a persistent challenge. Strengthening routine isoniazid resistance testing, expanding access to Xpert MTB/XDR, improving treatment adherence, and implementing targeted interventions with enhanced surveillance are essential to prevent resistance amplification, improve outcomes, and control Hr-TB spread..