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Table 2 Sequence results for discrepant samples

From: Performance of the G4 Xpert® MTB/RIF assay for the detection of Mycobacterium tuberculosis and rifampin resistance: a retrospective case-control study of analytical and clinical samples from high- and low-tuberculosis prevalence settings

a. Analytical study
 DST Result Xpert MTB/RIF assay result Number Sequence resulta
 RIF-resistant MTB not detected 3 MTB
 RIF-susceptible MTB not detected 1 MTB
 RIF-resistant RIF Resistance not detected 2 2 of 2 wild type rpoB core
 RIF-susceptible RIF Resistance detected 9 8 of 9 with resistance associated mutations in rpoB core: three with 531 ttg, three with 526 tgc, one with 516 gtc, one with 526 ctc 1 of 9 wild type rpoB core
b. Combined clinical studies
Culture/DST result Xpert MTB/RIF assay result Number Bi-directional sequencing
Smear-positive specimens
 MTB positive MTB not detected 1 MTB
 MTB negativeb MTB detected 1 N/A
Smear-negative specimens
 MTB positive MTB not detected 28 MTB
 MTB negativec MTB detected 7 N/A
Rifampin resistance results
 MTB positive/RIF- resistant MTB detected; RIF Resistance NOT detected 1 Resistance associated mutation in rpoB core: 531 ttg with evidence of wild type mixture
 MTB positive/RIF- susceptible MTB detected; RIF Resistance detected 4 2 of 4 with resistance associated mutations in rpoB core: both with 533 ccg
2 of 4 with susceptible associated rpoB core: one wild-type and one 514 ttt (silent) mutation.
  1. aCulture negativity was based on only one sputum specimen for this subject
  2. bCulture negativity classification was based on one sputum specimen for three subjects, two sputum specimens for two subjects and three sputum specimens for two subjects
  3. cIt is noted that DST did not detect some common mutations associated with rifampin resistance that were identified by sequencing. Several studies have demonstrated that testing the same strains with varying DST methodology can result in different rifampin resistance results [12, 2325]