Deciphering rifampicin resistance among tuberculosis patients who have trace results on Xpert MTB/RIF ultra assay

Introduction The Mycobacterium. tuberculosis (MTB) detected trace, rifampicin (RIF) resistance indeterminate category of the Xpert MTB/RIF Ultra assay results is usually, non-actionable and requires retesting the samples. We aimed to decipher RIF resistance among tuberculosis patients who have trace and indeterminate results.

Four hundred and three (403) MTB detected trace, RIF resistance indeterminate results, which were obtained in Mycobacteriology (BSL-3) and Molecular Diagnostic laboratories, College of Health Sciences, Makerere University from August 2018 to June 2023, having culture results were identified from the laboratory database. Isolates of those that turned out culture positive were retrieved and sub-cultured in liquid media to perform phenotypic first line Drug Susceptibility tests, first line Line-Probe assays (LPA) and repeat GeneXpert ultra.

A total of 31/403 (7.7%) culture positive isolates were identified from the database of which 77.42% (24/31) were positive for Mycobacterium tuberculosis complex (MTBc). Nineteen (19) out of the identified 24 MTBc were successfully retrieved, cultured and resistance testing performed. Phenotypic Drug susceptibility testing and repeated GeneXpert did not identify any resistance. Only one mutation inhA MUT1 related to isoniazid (INH) resistance was identified using MTBDRplus assay.

In this study, we did not identify any missed rifampicin resistance among MTBc culture positive samples that were initially Xpert ultra-trace and rifampicin resistance indeterminate. More studies with bigger sample sizes especially in high MDR-TB settings are required. Competing Interest Statement The authors have declared no competing interest. Funding Statement Yes Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Not Applicable The details of the IRB/oversight body that provided approval or exemption for the research described are given below: Makerere University, School of Biomedical Sciences Research and ethics Committee (SBS-2022-244) I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Not Applicable I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Not Applicable I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Not Applicable Data Availability All relevant data are within the manuscript and its Supporting Information files. Data availability statement All data generated or analyzed during this study are included in this published article