Department of Experimental, Diagnostic and Specialty Medicine - Unit of Microbiology, Alma Mater Studiorum University of Bologna - S. Orsola-Malpighi University Hospital, Bologna, Italy.
PLoS One. 2018 Aug 13;13(8):e0201934. doi: 10.1371/journal.pone.0201934. eCollection 2018.
The new Xpert MTB/RIF Ultra assay (Ultra, Cepheid, Sunnyvale, USA) is a cartridge-based automated diagnostic test that can simultaneously identify Mycobacterium tuberculosis complex (MTB) and resistance to Rifampicin (RIF). With respect to the previous version Xpert MTB/RIF assay (Xpert), IS6110/IS1081 repetitive elements probes have been added allowing the detection of lower MTB load, defined by the new semi-quantitative category "trace" with indeterminate RIF resistance. The aim of this study was to evaluate performance of the new version Ultra on Xpert-negative, but TB culture-positive clinical samples.
The de-identified frozen samples (-20 °C) collected over a 4-year period (February 2014-October 2017), which had previously resulted smear-negative, Xpert-negative but MTB culture-positive, were analyzed with Ultra. The de-frosted samples were loaded into the cartridge using the same process as the previous version, according to manufacturer's instruction.
During the study period 382 MTB culture-positive samples were archived: 314 resulted Xpert-positive and 68 Xpert-negative. Thirty-one of the 68 Xpert-negative samples resulted positive with Ultra, with an overall improvement in MTB detection of 45.6%. Out of 36 Xpert-negative respiratory samples, 18 resulted Ultra-positive with the following semi-quantitative loads: "low"(n = 1), "very low"(n = 11), "trace"(n = 6), with an improvement in MTB detection of 50%. The best performance was achieved on bronchoalveolar lavage specimens (53.8%). Out of 32 Xpert-negative non-respiratory samples, 13 resulted Ultra-positive with the following semi-quantitative loads: "very low"(n = 7), "trace"(n = 6), with an improvement in MTB detection of 40.6%. The best performance was achieved on biopsies (55.6%) and lymph nodes (50%). The new category "trace" detected 12 out of the 31 Ultra-positive MTB samples; in the remaining 19 samples RIF susceptibility was determined with 100% concordance with the phenotypic susceptibility test. The mean time to positivity of samples found negative by Ultra was significantly longer in comparison to positive samples in liquid culture.
Our results are consistent with the few studies published so far and confirm the better performance of Ultra compared to the previous version in both respiratory and non-respiratory smear-negative samples, with an overall improvement of 45.6%.
新的 Xpert MTB/RIF Ultra 检测（Ultra，Cepheid，美国桑尼维尔）是一种基于试剂盒的自动化诊断测试，可同时鉴定结核分枝杆菌复合群（MTB）和利福平耐药性（RIF）。与之前的 Xpert MTB/RIF 检测（Xpert）相比，已添加了 IS6110/IS1081 重复元件探针，从而可以检测到较低的 MTB 载量，新的半定量类别“痕迹”表示利福平耐药性不确定。本研究的目的是评估新版本 Ultra 在 Xpert 阴性但 MTB 培养阳性的临床样本中的性能。
在 4 年期间（2014 年 2 月至 2017 年 10 月）收集的已冷冻（-20°C）的、先前已确认涂片阴性、Xpert 阴性但 MTB 培养阳性的无身份识别样本，用 Ultra 进行分析。按照制造商的说明，使用与上一版本相同的流程将解冻的样本加载到试剂盒中。
在研究期间，共归档了 382 份 MTB 培养阳性样本：314 份 Xpert 阳性，68 份 Xpert 阴性。68 份 Xpert 阴性样本中有 31 份用 Ultra 检测呈阳性，MTB 检测总体改善率为 45.6%。在 36 份 Xpert 阴性的呼吸道样本中，18 份 Ultra 阳性，半定量负荷如下：“低”（n = 1）、“极低”（n = 11）、“痕迹”（n = 6），MTB 检测改善率为 50%。支气管肺泡灌洗液标本的检测效果最佳（53.8%）。在 32 份 Xpert 阴性的非呼吸道样本中，13 份用 Ultra 检测呈阳性，半定量负荷如下：“极低”（n = 7）、“痕迹”（n = 6），MTB 检测改善率为 40.6%。活检标本（55.6%）和淋巴结（50%）的检测效果最佳。新的“痕迹”类别检测到 31 份 Ultra 阳性 MTB 样本中的 12 份；在其余 19 份样本中，利福平药敏性与表型药敏试验的一致性为 100%。Ultra 检测为阴性的样本的阳性时间明显长于液体培养的阳性样本。
我们的结果与迄今为止发表的少数研究一致，证实了新版本 Ultra 在呼吸道和非呼吸道涂片阴性样本中的性能优于上一版本，总体改善率为 45.6%。
