Mansoori N, Pahlavanzadeh B, Arabmofrad F. Evaluation of the Xpert MTB/RIF test accuracy for diagnosis of tuberculosis in areas with a moderate tuberculosis burden. APMIS 2021; 125: 9-13. The Xpert MTB/RIF assay (Xpert) is a molecular assay used for direct detection of Mycobacterium tuberculosis (MTB) in clinical specimens. In this study, we aimed to assess the accuracy of the Xpert assay for the diagnosis of tuberculosis (TB) in TB suspected patients from the northern region of Iran. The obtained results were compared with the culture method. The sputum specimens were examined using the Xpert assay, smear microscopy, and solid culture media as a reference diagnostic tool. Among 293 presumptive TB cases, 92 (31.4%) were positive according to the culture method. The Xpert method detected 88 (95.7%) cases that were positive according to the culture method, compared with 78 (84.8%) positive cases according to smear microscopy. The overall sensitivity and specificity of the Xpert method for TB diagnosis were 95.7% and 99%, respectively. Also, the sensitivity and specificity for smear microscopy were 84.8% and 97.5%, respectively. The Xpert assay showed high overall sensitivity and specificity; thus, it can be effectively used for the early and accurate diagnosis of MTB in TB endemic areas. In addition, the agreement between semi-quantitative results of Xpert and smear microscopy assays could be helpful in evaluating transmission potential in TB patients.

Aim and objectives: Mycobacterium tuberculosis (MTB) is a causative agent of tuberculosis (TB) which remains as an endemic disease in Iran. One of the most significant steps for control of TB is the fast and accurate diagnosis of patients. Examination of sputum smears is the primary method for TB diagnosis, and the culture method remains as the gold standard. Recently, a molecular assay that named Xpert MTB/RIF assay (Xpert), was introduced for rapid diagnosis of TB. The aim of this study was to evaluate the performance of the Xpert assay for diagnosis of TB in Golestan province. Methods: The TB suspected cases which referred to Tuberculosis Reference laboratory, Gorgan, Iran, from March 2018 to February 2019 were included to this study. The sputum specimens were examined using smear microscopy after Ziehl–Neelsen staining and graded according to the International Union Against Tuberculosis and Lung Disease scale (scanty, 1+, 2+, 3+ and 4+). The Xpert analysis was performed according to the manufacturer's instructions and the provided semi-quantitative results for positive specimens (very low, low, medium and high) were documented. The specimens were cultured into Lowenstein-Jensen (LJ) culture media after decontamination by Petroff's method. Sensitivity and specificity of Xpert and smear microscopy were calculated using a culture as reference standard. Results: Of 102 presumptive TB cases, 17 (16.7%) had culture proven TB. The set of 16 (94·1%) culture-confirmed TB cases were equivalently detected using smear microscopy and Xpert. Compared to the culture method, specificity of Xpert and smear microscopy was 100% (85/85) and 97.6% (83/85), respectively. Both tests had a sensitivity of 94.1% (16/17). When the semi-quantitative results of Xpert were compared with smear microscopy, there was 92.3% agreement for specimens with medium/high results, with those that had 1+ to 3+ scales. Conclusion: The rapid and accurate laboratory diagnosis of TB is one of the most important steps for TB control programs. In this study, the Xpert was effectively used to early and accurate diagnosis of TB in the study area. In the other hand, correlation between the Xpert semi-quantitative results and smear microscopy showed that Xpert could help in evaluation of patient's transmission potential.