Evaluation of GeneXpert Assay for the Diagnosis of Childhood Pulmonary Tuberculosis from Stool Specimen at Jimma Medical Center, Southwest Ethiopia

Abstract

Background: Diagnosis of tuberculosis (TB) in children is challenging due to non-specific symptoms, difficulty of obtaining respiratory specimen and lack of sensitive diagnostic tests. The available TB diagnostic tests require sputum specimen, which is very difficult to obtain from young children. Other specimen like gastric aspirate (GA) can be applied to make microbiological diagnosis. However, these methods are complex, relatively invasive and often need the children to be hospitalized and overnight fasting. Thus, it needs alternative non-invasive specimens for diagnosis of pulmonary TB in children unable to produce sputum. Objective: To evaluate the diagnostic performance of Xpert assay for diagnosis of TB from stool specimen in children <15 years with presumptive pulmonary TB. Method: A cross-sectional study was conducted at Jimma University Medical Center from 1 st March to 30 th November 2019. Socio-demographic and clinical data of participants were collected using structured questionnaires. Expectorated sputum or GA specimens were collected and analyzed by Xpert assay and Lowenstein-Jensen ( LJ) culture. In addition, one stool specimen was collected from each child and tested by Xpert assay. Based on clinical, radiological and laboratory findings, patients were categorized into four groups: “confirmed TB”, “probable TB”, “possible TB”, and “not TB”. Diagnostic performance of stool Xpert was calculated with reference to LJ culture and composite reference standards (CRS). Results: A total of 178 children were enrolled, 169 had complete microbiological and clinical results. Male to female proportion was (81/88). The mean age was 3years, the majority 64.5% of the participant age was <5 years old. The overall microbiologically and clinically confirmed childhood TB proportion was 11.8% (20/169). Of these, 5.9% (10/169) had confirmed TB, 2.4% (4/169) had probable TB, 3.6% (6/169) had possible TB and 88.2% (149/169) had not-TB. Stool Xpert had sensitivity of 100% (95%CI: 66.4-100) and specificity of 99.3% (95%CI: 96.2-100) compared to culture. Whereas, the overall sensitivity and specificity of stool Xpert was 50% (95%CI: 27.2-72.8) and 100% (95%CI: 97.1-100) compared to CRS. Conclusions: Stool Xpert testing was improved sensitivity than GA Xpert testing that can be easily implemented at lowest level of health care system. However, a negative Xpert assay results may not exclude a diagnosis of TB in children and children with strong clinical findings suggestive of TB should be started on ant-TB treatment