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

Abstract

Young children cannot easily produce sputum for diagnosis of pulmonary tuberculosis. Alternatively, Mycobacterium tuberculosis complex (MTB) bacilli can be detected in stool by using the Xpert MTB/RIF (Ultra) assay (Xpert). Published stool processing methods contain somewhat complex procedures and 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 sputum Xpert testing for the detection of MTB in stool. We first assessed if the SOS stool method could provide valid Xpert results without the need of bead-beating, dilution and filtration steps. We concluded that this was the case and, subsequently, validated the SOS stool method by testing spiked stool samples. By using the SOS stool method, of the 29 spiked samples, 27 gave valid Xpert results and MTB was recovered from all 27. The proof of principle of the SOS stool method was demonstrated in a routine setting in Addis Ababa, Ethiopia. Nine of 123 children with presumptive TB were MTB positive on nasogastric aspirate (NGA), and seven (77.8%) of these also had an MTB positive Xpert result on stool. Additionally, MTB was detected in the stool but not on the NGA of two 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.

The Simple One-step stool processing method for detection of Pulmonary tuberculosis: a study protocol to assess the robustness, stool storage conditions and sampling strategy for global implementation and scale-up

“…This shows that there is a lack of standardized stool preparation and testing protocols and warrants the optimization and standardization of the stool processing methods that can be used at the decentralized level. The KNCV Tuberculosis Foundation (KNCV) and Ethiopian Public Health Institute (EPHI) developed the Simple One-Step (SOS) stool processing method, which can be applied in any GeneXpert laboratory (8).…”

“…The SOS method has shown to be successful, with a low rate of unsuccessful results reported, in a demonstration study conducted in Ethiopia, in which multiple laboratories were involved (8). Furthermore, a head-to-head comparison study, in which the SOS method is compared to other stool processing methods showed similar sensitivity and specificity.…”

“…This shows that there is a lack of standardized stool preparation and testing protocols and warrants the optimization and standardization of the stool processing methods that can be used at the decentralized level. The KNCV Tuberculosis Foundation (KNCV) and Ethiopian Public Health Institute (EPHI) developed the Simple One-Step (SOS) stool processing method, which can be applied in any GeneXpert laboratory (8). This SOS stool processing method uses similar steps as sputum Xpert testing and does not require additional materials or equipment other than an applicator to pick the correct stool amount for testing.…”

“…This SOS stool processing method uses similar steps as sputum Xpert testing and does not require additional materials or equipment other than an applicator to pick the correct stool amount for testing. Since the method is as simple as sputum Xpert processing, it can be performed at all sites where a GeneXpert instrument is functional after providing minimal training to the staff involved in Xpert testing (8).…”

“…The SOS method has shown to be successful, with a low rate of unsuccessful results reported, in a demonstration study conducted in Ethiopia, in which multiple laboratories were involved (8).…”