Diagnostic performance of Xpert MTB/RIF for sputum smear Mycobacterium tuberculosis infection and rifampin resistance,and analysis of drug resistance gene mutation characteristics

YAO Jianli; LI Qiuping; ZHANG Lina

doi:10.3969/j.issn.1007-8134.2025.03.001

Abstract：Objective To explore the diagnostic efficacy of real-time fluorescence quantitative nucleic acid amplification assay(Xpert MTB/RIF)for Mycobacterium tuberculosis(MTB)infection and rifampicin resistance in sputum smear-positive specimens,and to analyze the characteristics of drug-resistant gene mutations.Methods A total of 177 suspected tuberculosis patients admitted to the Third Hospital of Qinhuangdao from January 2020 to January 2022 were enrolled.The clinical diagnosis was regarded as the gold standard for confirming MTB infection.The positive rates of Xpert MTB/RIF were compared across different genders,age groups,sputum smear results and drug sensitivity test outcomes.The diagnostic efficiency of Xpert MTB/RIF for MTB infection and rifampicin resistance was evaluated by receiver operating characteristic(ROC)curve,with clinical diagnosis and absolute concentration method of drug susceptibility test as the gold standard.Additionally,the mutation characteristics of rpoB gene associated with rifampicin resistance in MTB were analyzed.The rpoB gene mutation rate and mutation characteristics of MTB with different genetic background and different degree of rifampicin resistance were further compared.Results Patients were divided into 5 groups according to quintiles of age.The positive rate of MTB infection in patients aged 23-56 years was significantly higher than that in other older age groups(P＜0.05).There was a significant difference between the results of Xpert MTB/RIF and the results of sputum smear and drug sensitivity(P＜0.05).The area under the ROC curve of Xpert MTB/RIF for the diagnosis of MTB infection was 0.876(95%CI:0.812-0.939),specifically,the sensitivity was 94.62%(88/93),the specificity was 84.52%(71/84),the positive predictive value was 87.13%(88/101),the negative predictive value was 93.42%(71/76),and the accuracy was 89.83%(159/177).The area under the ROC curve for the diagnosis of rifampicin resistance of MTB was 0.812(95%CI:0.753-0.882),the sensitivity was 74.19%(23/31),the specificity was 91.94%(57/62),the positive predictive value was 82.14%(23/28),the negative predictive value was 87.69%(57/65),and the accuracy was 86.02%(80/93).Among the 28 strains with rpoB gene mutations detected by Xpert MTB/RIF,the double-site mutations accounted for 3.23%(1/28),while the remaining were single-site mutations[96.43%(27/28)],and the predominant mutation type was at 531 site(TCG→TTG)[29.03%(9/28)].There was no significant difference in rpoB gene mutation rate or mutation type between non-Beijing genotype MTB and Beijing genotype MTB(all P＞0.05).By contrast,there were significant differences in the mutation rate of rpoB gene and the detection rate of mutation type 526(CAC→TAC)and 531(TCG→TTG)between the low concentration and high concentration resistant strains(P＜0.05).Conclusions Xpert MTB/RIF technique has high applicationvalue for MTB infection diagnosis in sputum smears and rifampicin resistance.Five hundred and thirty-one(TCG→TTG)mutation is the predominant type of rifampin resistant rpoB gene.