Background: The Xpert MTB/RIF Ultra (Xpert-Ultra) assay provides timely results with good sensitivity and acceptable specificity with stool specimens in children for bacteriological confirmation of tuberculosis (TB). This study aims to optimize the Simple One-Step (SOS) stool processing method for testing stool specimens using the Xpert-Ultra in children and adults in selected health facilities in Addis Ababa, Ethiopia. The study is designed to assess the robustness of the SOS stool method, to help fine-tune the practical aspects of performing the test and to provide insights in stool storage conditions and sampling strategies before the method can be implemented and scaled in routine settings in Ethiopia as well as globally.
Methods and design: The project "painless optimized diagnosis of TB in Ethiopian children" (PODTEC) will be a cross sectional study where three key experiments will be carried out focusing on 1) sampling strategy to investigate if the Xpert-Ultra M. tuberculosis (MTB) -positivity rate depends on stool consistency, and if sensitivity can be increased by taking more than one stool specimen from the same participant, or doing multiple tests from the same stool specimen, 2) storage conditions to determine how long and at what temperature stool can be stored without losing sensitivity, and 3) optimization of sensitivity and robustness of the SOS stool processing method by varying stool processing steps, stool volume, and storage time and conditions of the stool-sample reagent mixture. Stool specimens will be collected from participants (children and adults) who are either sputum or naso-gastric aspiration (NGA) and/or stool Xpert-Ultra MTB positive depending on the experiment. Stool specimens from these participants, recruited from 22 sites for an ongoing related study, will be utilized for the PODTEC experiments. The sample size is estimated to be 50 participants. We will use EpiData for data entry and Stata for data analysis purposes. The main analyses will include computing the loss or gain in the Xpert-Ultra MTB positivity rate and rates of non-determinate Xpert-Ultra test results per experiment compared to the Xpert-Ultra MTB result of stool processed according to the published standard operating procedures for SOS stool processing. The differences in the MTB positivity rate by regarding testing more than one sample per child, and using different storage, and processing conditions, will be also compared to the baseline (on-site) Xpert-Ultra result.