Dependence of Xpert MTB/RIF Accuracy for Detecting Rifampin Resistance in Bronchoalveolar Lavage Fluid on Bacterial Load: A Retrospective Study in Beijing, China

Abstract

Introduction We assessed the effect of Mycobacterium tuberculosis (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. Methods 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 t -test were used to compare results across groups stratified according to BALF bacterial load. Results 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 ( P <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%, P <0.05). Sanger sequencing data obtained for 20 (32.8%) MTB isolates deemed RIF-resistant via Xpert (Probe E) lacked rpoB 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 rpoB RRDR mutations, while sequences of the remaining 3 isolates harbored single rpoB RRDR mutations predicted to cause amino acid substitutions. Conclusion 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.

Factors influencing false-positive results of rifampicin resistance detected by Xpert MTB/RIF: A retrospective study in Zhejiang, China

“…In 2016, Ocheretina et al investigated 22 TB patients, revealing that the Xpert test was more likely to produce false-positive results for RIF-R in clinical samples with extremely low bacterial loads [ 19 ]. Subsequently, studies from Beijing, China, and Rwanda have confirmed this finding [ 21 , 22 ]. In contrast, Berhanu et al, using “medium” load as a reference, revealed similar levels of discordance as observed in “very low” samples, using Xpert testing (IRR = 1.22, 95 % CI 0.4–3.70) [ 13 ].…”

The use of rats to detect drug-resistant TB

“…According to recent reports, the MTB/RIF assay performed poorly and displayed higher variability when used to detect RR-MTB among samples with very low MTB bacillary loads. 5,6 Ngabonziza et al suggested that RR-positive tests should be repeated with a second sample, and whenever inconsistent initial and repeat MTB/RIF test results were reported, false-positive RR-TB should be ruled out before treatment initiation. 7 In the present study, Ultra was used, which is apparently unaffected by very low bacillary loads.…”

Apport Du Genexpert MTB/Rif Dans La Detection De L’infection a Mycobacterium Tuberculosis Et La Resistance a La Rifampicine a L’hopital General De Reference De Kirungu-Moba, Sud-Est De La Republique Democratique Du Congo

“…La tuberculose est une maladie infectieuse causée par le Mycobacterium tuberculosis, capable d'affecter tous les tissus humains [1], [2]. Elle demeure à ce jour un problème de santé publique, avec 10,6 millions des cas notifiés (une nette augmentation par rapport à 2020) et 1,6 millions de décès en 2021 [3], [4].…”

“…Pour y arriver, il faut des tests rapides et précis recommandés par l'OMS : BACTER MGIT 960 SIRE, Geno Type MTBDR Plus, Xpert MTB/RIF[64],[65]. Il faut cependant souligner des faux résultats de résistance des médicaments d'usage dans la lutte contre la tuberculose au GeneXpert qui ont été soulignés par certaines auteurs[2],[66]-[69], d'où la politique de prudence par des tests moléculaires répétés pour retenir des vrais cas de résistance à la Rifampicine. Pour Ngabonziza et al[67] au Rwanda, Beylis et al[70] en Afrique du Sud et Liu et al[71] en Chine, les faux résultats de la TB-RR seraient en rapport avec les cas de tuberculose pulmonaire pauci bacillaires.…”

“…Pour Ngabonziza et al[67] au Rwanda, Beylis et al[70] en Afrique du Sud et Liu et al[71] en Chine, les faux résultats de la TB-RR seraient en rapport avec les cas de tuberculose pulmonaire pauci bacillaires. Par contre, Qi et al[2] souligne que l'échec de l'hybridation de la sonde Xpert E est à l'origine des faux TB-RR. De ce fait, les limites du GeneXpert (première méthode de recours) doivent être connues des personnels soignants et des acteurs de prise de décision en santé publique[66].…”