Introduction:

it is typically stated that the diagnosis of tuberculosis (TB) is clinical, epidemiological, radiological, and confirmed by bacteriology. Globally, confirmation of the diagnosis is achieved in approximately 80% of patients. Confirmation of the disease in children is limited due to its paucibacillary presentation and the difficulty in obtaining quality respiratory samples. In 2022, the WHO recommended the use of Xpert MTB/RIF in fecal matter in children. Compared to a microbiological standard, the reported sensitivity and specificity are 61% and 98%, respectively; however, when compared to a composite clinical standard, the sensitivity decreases to 16% and the specificity hardly varies (99%).

Objectives:

to evaluate the application of the Xpert MTB/RIF Ultra in fecal samples for the confirmation of tuberculosis in children.

Methodology:

descriptive, retrospective study. The databases of the National Reference Laboratory for Mycobacteria and the National Tuberculosis Registry (NTR) were reviewed. All fecal samples from children under 20 years of age that underwent Xpert MTB/RIF Ultra between 10/1/2022 and 9/30/2024 were analyzed. The inclusion of children or adolescents in the NTR and the initiation of antituberculosis therapy was taken as the clinical standard. The Open Epi version 3.01 program was used to calculate sensitivity, specificity, and positive (PPV) and negative (NPV) predictive values.

Results:

in the studied period, 74 samples from children and adolescents that underwent Xpert MTB/RIF Ultra were identified. 14 (19%) samples had an invalid or error result. Two positive results were identified; one with trace load and the other with medium load. A sensitivity of 15.38% (95%CI 4.326-42.24), a specificity of 100% (95%CI 92.44 - 100), PPV of 100% (95%CI 34.24 - 100) and NPV of 81.03 (95%CI 69.15 89.07) was calculated compared to the defined clinical standard. A microbiological standard could not be used given the high percentage of contaminated cultures (66.6%).

Conclusions:

the use of fecal matter appears to be an attractive option for the confirmation of tuberculosis in children given its easy collection. However, its application has a high percentage of error/invalid results, well above the maximum expected 3%. Although sensitivity and PPV are excellent, the sensitivity and NPV of the technique are very low. The use of fecal matter should be limited to those patients in whom it is impossible to obtain any other type of sample for diagnosis confirmation.

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