Optimization of the Simple One-Step Stool Processing Method to Diagnose Tuberculosis: Evaluation of Robustness and Stool Transport Conditions for Global Implementation

ABSTRACT Stool is recommended as an alternative specimen for the diagnosis of tuberculosis (TB) in young children, as they cannot easily produce sputum. The Simple One-Step (SOS) stool processing method is a new and simple stool processing method for the detection of Mycobacterium tuberculosis (MTB) using Xpert MTB/RIF Ultra (Xpert-Ultra). We determined the robustness of the SOS stool processing method and stool specimen transport conditions in participants with confirmed TB. We processed stool using the standard protocol after simulated “transport,” varying time, and temperature, and experimented with slightly modified processing steps. We included 2,963 Xpert-Ultra test results from 132 stool specimens of 47 TB participants, including 11 children aged 0.8 g of stool. We found that almost all steps in the current SOS stool processing method provide optimal Xpert-Ultra results but recommend an adjustment to use a wider range of stool amounts (0.3 to 0.8 g) than advised previously (0.8 g). With this adaptation, stool-based diagnosis of TB using the SOS stool processing method can be scaled-up. IMPORTANCE The manuscript will support the global implementation and scale-up of the SOS stool method in routine settings. It also provides important insights on the optimal stool transport conditions and robustness of the SOS method, which can be used for bacteriological diagnosis of TB in children at the lowest levels of the healthcare system, avoiding lengthy healthcare-seeking pathways and additional costs

The Simple One-Step (SOS) Stool Processing Method for Use with the Xpert MTB/RIF Assay for a Child-Friendly Diagnosis of Tuberculosis Closer to the Point of Care

International audienceYoung children cannot easily produce sputum for diagnosis of pulmonary tuberculosis (TB). Alternatively, Mycobacterium tuberculosis complex bacilli can be detected in stool by using the Xpert MTB/RIF (Ultra) assay (Xpert). Published stool processing methods contain somewhat complex procedures and require additional supplies. The aim of this study was to develop a simple one-step (SOS) stool processing method based on gravity sedimentation only, similar to Xpert testing of sputum samples, for the detection of M. tuberculosis in stool samples. We first assessed whether the SOS stool method could provide valid Xpert results without the need for bead-beating, dilution, and filtration steps. We concluded that this was the case, and we then validated the SOS stool method by testing spiked stool samples. By using the SOS stool method, 27 of the 29 spiked samples gave valid Xpert results, and M. tuberculosis was recovered from all 27 samples. The proof of principle of the SOS stool method was demonstrated in routine settings in Addis Ababa, Ethiopia. Nine of 123 children with presumptive TB had M. tuberculosis-positive results for nasogastric aspiration (NGA) samples, and 7 (77.8%) of those children also had M. tuberculosis-positive Xpert results for stool samples. Additionally, M. tuberculosis was detected in the stool samples but not the NGA samples from 2 children. The SOS stool processing method makes use of the standard Xpert assay kit, without the need for additional supplies or equipment. The method can potentially be rolled out to any Xpert site, bringing a bacteriologically confirmed diagnosis of TB in children closer to the point of care

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