Lung Infection and Immunity Unit, Division of Pulmonology and UCT Lung Institute, Department of Medicine, University of Cape Town, Cape Town, South Africa.
Am J Respir Crit Care Med. 2011 Jul 1;184(1):132-40. doi: 10.1164/rccm.201101-0056OC. Epub 2011 Apr 14.
RATIONALE: Xpert MTB/RIF is a novel automated molecular diagnostic recently endorsed by the World Health Organization. However, performance-related data from high HIV prevalence settings are limited. OBJECTIVES: The impact of sample-related factors on performance and the significance of Xpert MTB/RIF-positive culture-negative discordance remain unclear. METHODS: Xpert MTB/RIF was evaluated using single archived spot-sputum samples from 496 South African patients with suspected TB. Mycobacterium tuberculosis culture positivity and phenotypic resistance to rifampicin served as reference standards. MEASUREMENTS AND MAIN RESULTS: Overall, Xpert MTB/RIF detected 95% (95% confidence interval [CI], 88-98%; 89 of 94) of smear-positive culture-positive cases and the specificity was 94% (91-96%; 320 of 339). The sensitivity in smear-negative cases was 55% (35-73%; 12 of 22) when the analysis was restricted to 1 ml of unprocessed sputum and culture time-to-positivity of less than or equal to 28 days. Compared with smear microscopy (n=94), Xpert MTB/RIF detected an additional 17 cases (n=111) representing an 18% (11-27%; 111 vs. 94) relative increase in the rapid TB case detection rate. Moreover, compared with smear microscopy, the inclusion of Xpert MTB/RIF-positive culture-negative TB cases (ruled-in by an alternative diagnostic method) resulted in the detection of a further 16 cases (n=127), thus significantly increasing the rapid TB case detection rate to 35% (95% CI, 26-45%; 94 to 111 vs. 94 to 127; P<0.01), the overall specificity to 99.1% (97-100%; 320 of 323; P<0.001), and sensitivity in smear-negative TB to 60% (P=0.12). Performance strongly correlated with smear status and culture time-to-positivity. In patients infected with HIV compared with patients uninfected with HIV Xpert MTB/RIF showed a trend to reduced sensitivity (P=0.09) and significantly reduced negative predictive value (P=0.01). The negative predictive value for rifampicin resistance was 99.4%. CONCLUSIONS: XpertMTB/RIF outperformed smear microscopy, established a diagnosis in a significant proportion of patients with smear-negative TB, detected many highly likely TB cases missed by culture, and accurately ruled out rifampicin-resistant TB. Sample-specific factors had limited impact on performance. Performance in patients infected with HIV, especially those with advanced immunosuppression, warrants further study.
背景：Xpert MTB/RIF 是一种新型自动化分子诊断技术，最近得到世界卫生组织的认可。然而，来自高 HIV 流行地区的与性能相关的数据有限。
目的：样本相关因素对性能的影响以及 Xpert MTB/RIF 阳性而培养阴性的不相符的意义仍不清楚。
方法：使用来自南非 496 名疑似结核病患者的单个存档点痰样本评估 Xpert MTB/RIF。分枝杆菌结核培养阳性和表型对利福平的耐药性作为参考标准。
测量和主要结果：总体而言，Xpert MTB/RIF 检测到 95%（95%置信区间[CI]，88-98%；94 例中有 89 例）的涂片阳性培养阳性病例，特异性为 94%（91-96%；339 例中有 320 例）。当分析仅限于 1 毫升未经处理的痰液且培养至阳性的时间≤28 天时，在涂片阴性病例中，灵敏度为 55%（35-73%；22 例中有 12 例）。与涂片显微镜检查（n=94）相比，Xpert MTB/RIF 检测到另外 17 例（n=111），即快速结核病检测率相对增加了 18%（11-27%；111 比 94）。此外，与涂片显微镜检查相比，包括 Xpert MTB/RIF 阳性而培养阴性的结核病病例（通过替代诊断方法确定）又检测到 16 例（n=127），从而使快速结核病检测率显著增加到 35%（95%CI，26-45%；94 比 111 比 94 比 127；P<0.01），总体特异性提高到 99.1%（97-100%；320 比 323；P<0.001），且涂片阴性结核病的灵敏度提高到 60%（P=0.12）。性能与涂片状态和培养至阳性的时间密切相关。与未感染 HIV 的患者相比，感染 HIV 的患者的 Xpert MTB/RIF 显示出敏感性降低的趋势（P=0.09），并且阴性预测值显著降低（P=0.01）。利福平耐药的阴性预测值为 99.4%。
结论：XpertMTB/RIF 优于涂片显微镜检查，为相当一部分涂片阴性结核病患者建立了诊断，检测到许多培养遗漏的高度可能的结核病病例，并准确排除了利福平耐药结核病。样本特异性因素对性能的影响有限。在感染 HIV 的患者中，尤其是在严重免疫抑制的患者中，其性能仍需进一步研究。
Am J Respir Crit Care Med. 2011-4-14
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