Abstract:

Objective To compare the results of Mycobacterium tuberculosis (MTB) resistance to rifampicin (RFP) by Micropore-plate method (Microdrug sensitivity, MicroDST) and GeneXpert MTB/RIF test. Methods Among the 6893 suspected MTB patients who admitted to or visited Outpatient Department in Shaanxi Provincial Tuberculosis Control and Prevention Hospital, 6086 patients were diagnosed as MTB cases according to the clinical diagnostic criteria. A total of 425 clinical specimens were tested by BACTEC MGIT 960 liquid culture method and GeneXpert method, including 217 sputum specimens, 170 alveolar lavage specimens, and 38 extrapulmonary fluid specimens (such as pleural and peritoneal effusion, pus and cerebrospinal fluid). After excluding 3 specimens that reported errors or could not be interpreted and 2 specimens that were contaminated when cultured, there were 420 valid specimens. Three hundred and seventy-two clinical isolates with positive results by GeneXpert and MGIT 960 method were tested for drug resistance by MicroDST, GeneXpert MTB/RIF and MGIT 960 method, including 191 sputum specimens, 158 alveolar lavage specimens, and 23 extrapulmonary fluid specimens (such as pleural and peritoneal effusion, pus and cerebrospinal fluid). Taking MGIT 960 test as the gold standard, the performance of MicroDST and GeneXpert MTB/RIF in detecting MTB resistance to RFP were compared. Results The overall positive rates of RFP resistance by GeneXpert MTB/RIF, MicroDST and MGIT 960 method were 18.8% (70/372), 16.7% (62/372), and 16.7% (62/372), respectively. Taking MGIT 960 test as the gold standard, the sensitivity, specificity, coincidence rate and Kappa value of RFP resistance test were 91.9% (57/62), 98.4% (305/310), 97.3% (362/372) and 0.8 by MicroDST assay and 96.8% (60/62), 96.8% (300/310), 96.8% (360/372) and 0.8 by GeneXpert MTB/RIF assay. The sensitivity, specificity, coincidence rate and Kappa value using sputum, alveolar lavage and extrapulmonary specimens were 96.7% (29/30), 98.1% (158/161), 97.9% (187/191), 0.9; 93.3% (28/30), 96.3% (155/161), 95.8% (183/191), 0.9; and 91.7% (22/24), 98.5% (132/134), 97.5% (154/158), 0.9 by MicroDST assay and 100.0% (24/24), 97.0% (130/134), 97.5% (154/158), 0.9; 75.0% (6/8), 100.0% (15/15), 91.3% (21/23), 0.8; and 100.0% (8/8), 100.0% (15/15), 100.0% (23/23), 1.0 by GeneXpert MTB/RIF assay, respectively. Conclusion Taking MGIT 960 test as the gold standard, MicroDST and GeneXpert MTB/RIF assay have a good consistency in overall positive detection rate of RFP resistance, as well as in different samples.

Key words: Mycobacterium tuberculosis, Rifampin, Tuberculosis,multidrug-resistant, Nucleic acid amplification techniques, Microbial sensitivity tests, Comparative study