Diagnostic accuracy of sputum smear microscopy compared with culture in patients with tuberculosis confirmed by Xpert <i>Mycobacterium tuberculosis</i> /rifampicin assay in Tanzania: A cross-sectional study

ObjectiveTo assess the diagnostic accuracy of sputum smear microscopy compared with culture in patients who were already confirmed positive for tuberculosis by Xpert <i>Mycobacterium tuberculosis</i>/rifampicin assay in Tanzania.MethodsA cross-sectional study was conducted across five tuberculosis clinics in Dar es Salaam. Adults (aged 18-80 years) with symptoms of tuberculosis and a positive Xpert <i>Mycobacterium tuberculosis</i>/rifampicin assay result provided additional sputum specimens for smear microscopy using Ziehl-Neelsen staining and culture on Löwenstein-Jensen medium, processed at the Central Tuberculosis Reference Laboratory, Muhimbili National Hospital.ResultsWe enrolled 200 participants, with a median age of 35 (interquartile range: 27-46) years; 74.5% of them were male. Using culture as the reference, Ziehl-Neelsen smear microscopy showed a sensitivity of 86.6% and a specificity of 40.7%. The Xpert <i>Mycobacterium tuberculosis</i>/rifampicin assay showed higher diagnostic accuracy. Notably, 43% of smear-negative cases were culture-positive, indicating that smear microscopy alone led to a substantial proportion of missed diagnoses. The Ziehl-Neelsen smear's receiver operating characteristic curve had an area under the curve of 0.64, indicating moderate performance.ConclusionThis study underscores the limitations of smear microscopy and highlights the operational utility of Xpert <i>Mycobacterium tuberculosis</i>/rifampicin assay. In regions where Xpert Ultra remains inaccessible, combining Xpert with culture selectively may enhance detection in low-resource settings.