Clinical application of a new-generation Xpert Mycobacterium tuberculosis/rifampin Ultra cartridge

Abstract

Objective To investigate the clinical value of a new-generation cartridge Xpert MTB/RIF Ultra assay on detection of Mycobacterium tuberculosis (MTB) and rifampin(RIF) resistance. Methods A total of 111 patients from He′nan Provincial Chest Hospital with suspected tuberculosis(TB) and retreated TB were enrolled into this study from March to December 2016, including 33 cases of tuberculosis detection group(CDG) and 78 cases of drug resistant high-risk group (DRG). The sputum samples of patients were collected. The sensitivity and specificity of Xpert MTB/RIF Ultra, sputum smear, solid Lowenstein-Jensen (L-J) culture and mycobacterial growth indicator tube(MGIT) culture for MTB were evaluated. RIF resistance was performed by Xpert MTB/RIF Ultra, traditional phenotypic drug sensitivity test and Xpert MTB/RIF assay. Measurement data were compared using t-test, and categorical data were compared using chi-squared test. Results Using clinical diagnosis result as the standard, in the CDG, the sensitivity of Xpert MTB/RIF Ultra for MTB detection (75.8%) was not significantly different from those of sputum smear (66.7%), L-J culture(63.6%), MGIT culture(75.6%) and Xpert MTB/RIF (66.7%)(χ2=0.67, 1.15, 0.00 and 0.67, respectively, all P>0.05). In the DRG, the sensitivity of Xpert MTB/RIF Ultra (94.9%) was better than those of L-J culture (55.1%) and MGIT culture (80.8%) with statistical significance (χ2=32.8 and 7.25, respectively, both P 0.05). Xpert MTB/RIF Ultra took the shortest time to obtain the final results, which was (1.76±0.18) h and significantly shorter than smear test ([5.04±0.49] h), L-J culture ([31.67±0.56] h), MGIT culture ([22.36±9.68] h), Xpert MTB/RIF ([2.00±0.30] h) (t =16.90, 31.98, 24.38 and 7.05, respectively, all P<0.01). Using culture result as the standard, the sensitivity for MTB detection of Xpert MTB/RIF and Xpert MTB/RIF Ultra were 93.2% and 98.9%, and the specificity of Xpert MTB/RIF and Xpert MTB/RIF Ultra were both 100%. The sensitivity for MTB detection of Xpert MTB/RIF Ultra (52.2%) was significantly better than that of Xpert MTB/RIF (21.7%) in 23 smear-negative pulmonary TB patients with statistical significance (χ2=4.98, P=0.025). Using traditional drug susceptibility test as the standard, the sensitivities for RIF resistance detection of Xpert MTB/RIF and Xpert MTB/RIF Ultra in culture-positive TB patients were 90.9% and 93.2%, respectively, and the specificities were 89.5% and 92.9%, respectively. Conclusions Xpert MTB/RIF Ultra has a higher MTB detection rate than Xpert MTB/RIF in smear-negative pulmonary TB patients. In drug-resistant pulmonary TB patient, MTB/RIF Ultra has high sensitivity, and it takes shorter time to detect MTB and RIF resistance. Thus, Xpert MTB/RIF Ultra has a good application prospect in clinical work. Key words: Mycobacterium tuberculosis; Tuberculosis, pulmonary; Diagnosis; Rifampin; Drug resistance, bacterial; Microbial sensitivity tests; Nucleic acid amplification techniques