Department of Tuberculosis, Beijing Chest Hospital, Capital Medical University/Beijing Tuberculosis & Thoracic Tumor Research Institute, Beijing 101149, People's Republic of China.
Department of Bacteriology and Immunology, Beijing Key Laboratory on Drug-Resistant Tuberculosis Research, Beijing Chest Hospital, Capital Medical University/Beijing Tuberculosis & Thoracic Tumor Research Institute, Beijing 101149, People's Republic of China.
J Infect Public Health. 2023 Jun;16(6):911-916. doi: 10.1016/j.jiph.2023.04.004. Epub 2023 Apr 7.
The Xpert MTB/RIF (Xpert) assay has been widely used to diagnose suspected active tuberculosis (TB) and rifampicin-resistant TB cases. Despite its excellent performance record, false-positive Xpert rifampicin (RIF) resistance results are obtained for specimens with extremely low bacterial loads.
We aimed to study the feasibility of repeat Xpert testing as a strategy for reducing the odds of obtaining false-positive results when testing paucibacillary TB patients.
We enrolled previously tested TB patients with very low initial bacterial loads from May 2016 to February 2022 for Xpert retesting. A total of 251 TB patients were retested using the Xpert assay.
RIF resistance was noted in 65 (25.9 %) patients when tested by Xpert at initial diagnosis. Only 107 (42.6 %) of 251 patients tested positive for MTB when retested via Xpert. The majority (98.6 %) of RIF-susceptible cases were still susceptible to RIF when retested. Initial Xpert testing yielded 35 positive results for MTB in the RIF-resistant group, of whom 25 (71.4 %) still exhibited RIF resistance when retested. All culture-positive MTB isolates in the RIF-susceptible group were also RIF-susceptible by phenotypic DST. In the RIF-resistant group, 10 of 14 culture-positive MTB isolates exhibited RIF resistance, of which 4 isolates were deemed RIF-susceptible by phenotypic DST. The proportion of double mutations within the MTB rpoB RRDR sequence, as detected by hybridization of Xpert D and E probes, was significantly higher in the RIF-susceptible group than in the RIF-susceptible group.
Our results demonstrated that initial RIF-susceptible results were more accurate than RIF-resistant results. Additionally, patients with double mutations that delayed probe D/E hybridization were more likely to have false-positive Xpert results. Our findings emphasize that repeat Xpert MTB/RIF testing is necessary for TB patients with extremely low bacterial loads who are at high risk for RIF-resistant TB.
Xpert MTB/RIF（Xpert）检测已广泛用于诊断疑似活动性肺结核（TB）和利福平耐药 TB 病例。尽管其性能记录优异，但极低细菌负荷的标本会获得假阳性的 Xpert 利福平（RIF）耐药结果。
我们旨在研究重复 Xpert 检测作为减少检测低细菌负荷性肺结核患者获得假阳性结果几率的策略的可行性。
我们招募了 2016 年 5 月至 2022 年 2 月期间具有极低初始细菌负荷的既往检测过的 TB 患者进行 Xpert 重复检测。共有 251 例 TB 患者接受了 Xpert 检测。
在初始诊断时，通过 Xpert 检测发现 65 例（25.9%）患者存在 RIF 耐药。在 251 例患者中，只有 107 例（42.6%）通过 Xpert 再次检测为 MTB 阳性。大多数（98.6%）RIF 敏感病例再次检测时仍对 RIF 敏感。在 RIF 耐药组中，初始 Xpert 检测有 35 例 MTB 阳性结果，其中 25 例（71.4%）再次检测时仍存在 RIF 耐药。RIF 敏感组中所有培养阳性的 MTB 分离株经表型 DST 检测均对 RIF 敏感。在 RIF 耐药组中，14 例培养阳性的 MTB 分离株中有 10 例表现出 RIF 耐药，其中 4 例经表型 DST 检测认为对 RIF 敏感。杂交 Xpert D 和 E 探针检测到的 MTB rpoB RRDR 序列内双突变的比例，在 RIF 敏感组显著高于 RIF 耐药组。
我们的结果表明，初始 RIF 敏感结果比 RIF 耐药结果更准确。此外，探针 D/E 杂交延迟的双突变患者更有可能出现假阳性 Xpert 结果。我们的研究结果强调，对于具有极高 RIF 耐药风险且细菌负荷极低的 TB 患者，重复 Xpert MTB/RIF 检测是必要的。
