Qin Lin, Huo Fengmin, Ren Weicong, Shang Yuanyuan, Yao Cong, Zhang Xuxia, Liu Rongmei, Ma Liping, Gao Mengqiu, Pang Yu
Department of Endoscopic Diagnosis & Treatment, Beijing Chest Hospital, Capital Medical University/Beijing Tuberculosis & Thoracic Tumor Research Institute, Beijing, 101149, People's Republic of China.
Department of Bacteriology and Immunology, Beijing Key Laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University/Beijing Tuberculosis & Thoracic Tumor Research Institute, Beijing, 101149, People's Republic of China.
Infect Drug Resist. 2021 Jun 28;14:2429-2435. doi: 10.2147/IDR.S307488. eCollection 2021.
We assessed the effect of (MTB) bacterial load on Xpert MTB/RIF accuracy for detection of rifampicin (RIF)-resistant MTB in bronchoalveolar lavage fluid (BALF) specimens obtained at a national tuberculosis (TB) specialized hospital in Beijing, China.
A retrospective study was conducted at Beijing Chest Hospital. Patients with symptoms suggestive of pulmonary TB who provided BALF specimens for routine MTB detection between June 2019 and July 2020 were enrolled in the study. Chi-square test and Student's -test were used to compare results across groups stratified according to BALF bacterial load.
In total, 1125 patients with positive Xpert results who were enrolled in final analysis, 263 provided BALF specimens that tested positive for RIF-resistant MTB via Xpert MTB/RIF. The RIF-resistance rate of specimens with very low MTB bacterial load was 30.9%, a resistance rate significantly greater than rates obtained for groups with high (25.0%), medium (17.3%) and low (19.2%) MTB loads (<0.01). Notably, false-positive results obtained for the very low bacterial load group led to markedly reduced positive predictive value of Xpert MTB/RIF to provide correct RIF-resistance predictions for that group (67.1%, 95% CI: 56.1%-78.1%5) relative to the predictive value obtained for all other groups combined (about 90%, <0.05). Sanger sequencing data obtained for 20 (32.8%) MTB isolates deemed RIF-resistant via Xpert (Probe E) lacked RRDR mutations. Meanwhile, of another group of 23 isolates deemed RIF-susceptible via DST but RIF-resistant via Xpert MTB/RIF, 20 isolate sequences (87.0%) lacked RRDR mutations, while sequences of the remaining 3 isolates harbored single RRDR mutations predicted to cause amino acid substitutions.
Xpert MTB/RIF assay performed alarmingly poorly when used to detect RIF-resistant MTB in BALF specimens with very low bacterial loads. A high rate of Xpert probe E hybridization failure was the main driver of false-positive RIF-resistant results.
我们评估了结核分枝杆菌（MTB）细菌载量对Xpert MTB/RIF检测中国北京一家国家级结核病专科医院获取的支气管肺泡灌洗液（BALF）标本中耐利福平（RIF）MTB准确性的影响。
在北京胸科医院进行了一项回顾性研究。纳入了2019年6月至2020年7月间因疑似肺结核症状而提供BALF标本用于常规MTB检测的患者。采用卡方检验和学生t检验比较根据BALF细菌载量分层的各组结果。
最终纳入1125例Xpert检测结果为阳性的患者进行分析，其中263例患者的BALF标本经Xpert MTB/RIF检测为耐RIF MTB阳性。MTB细菌载量极低的标本的RIF耐药率为30.9%，该耐药率显著高于高（25.0%）、中（17.3%）、低（19.2%）MTB载量组（P<0.01）。值得注意的是，细菌载量极低组的假阳性结果导致Xpert MTB/RIF为该组提供正确RIF耐药预测的阳性预测值显著降低（67.1%，95%CI：56.1%-78.1%），相对于其他所有组合组获得的预测值（约90%，P<0.05）。通过Xpert（探针E）判定为耐RIF的20株（32.8%）MTB分离株的桑格测序数据缺乏RRDR突变。同时，另一组经DST判定为RIF敏感但经Xpert MTB/RIF判定为耐RIF的23株分离株中，20株（87.0%）的序列缺乏RRDR突变，其余3株的序列含有预测会导致氨基酸替换的单个RRDR突变。
当用于检测细菌载量极低的BALF标本中的耐RIF MTB时，Xpert MTB/RIF检测表现极差。Xpert探针E杂交失败率高是耐RIF假阳性结果的主要原因。
