Stool processing methods for Xpert Ultra testing in childhood tuberculosis: A prospective, multi-country accuracy study.

Background: Centrifuge-free processing methods support stool Xpert Ultra testing for childhood tuberculosis (TB), but there are limited data on their accuracy, acceptability and usability. Methods: We conducted a prospective evaluation of stool Xpert Ultra in India, South Africa, and Uganda with three methods: Stool Processing Kit (SPK), Simple One-Step (SOS), and Optimized Sucrose Flotation (OSF). Children <15 years old with presumptive TB had respiratory specimen testing with Xpert Ultra and culture. Stool was tested using Xpert Ultra after processing with each method. We compared the accuracy of each method to a microbiological reference standard (MRS) and a composite reference standard (CRS). We surveyed the laboratory staff to assess acceptability and usability of the methods. Results: We included 607 children, of whom the median age was 3.5 years (IQR 1.3-7), 48% were female, and 15.5% were HIV positive. Against the MRS, the sensitivities of SPK, SOS and OSF were 36.9% (95% CI 28.6-45.8), 38.6% (95% CI 17.2-51), and 31.3% (95% CI 20.2-44.1), respectively. The specificities of SPK, SOS and OSF were 98.2% (95% CI 96.4-99.3), 97.3% (95% CI 93.7-99.1) and 97.1% (95% CI 93.3-99), respectively. Laboratory staff reported that the methods were acceptable and usable, but SOS was most feasible to implement in a peripheral facility. Sensitivity increased among children who were culture-positive (55-77.3%) and was low (13-16.7%) against the CRS. Conclusions: Stool processing methods for Xpert Ultra were acceptable, usable, and performed similarly, with highest sensitivity among children with culture-positive TB.