Xpert MTB/RIF assay for the diagnosis of extrapulmonary tuberculosis: a diagnostic evaluation study

ObjectivesThe diagnosis of extrapulmonary tuberculosis (EPTB) is often made on clinical suspicion alone, resulting in both under- and overdiagnosis and relatively poor outcomes. In this study, we evaluated the clinical utility of the Xpert MTB/RIF on routinely collected extrapulmonary specimens in Ethiopia.MethodsThis study was carried out at Jimma University Specialized Hospital, Southwest Ethiopia. Extrapulmonary specimens were collected from 572 patients clinically suspected of suffering from EPTB. All specimens were tested for TB by smear microscopy, culture, and Xpert MTB/RIF. The diagnostic accuracy of Xpert MTB/RIF was calculated and compared to a composite reference standard (CRS), comprising clinical and laboratory results.ResultsIn total, 572 extrapulmonary specimens (279 lymph node, 159 pleural, 80 peritoneal, 45 cerebrospinal, and nine pericardial fluids) were tested. The pooled sensitivity and specificity of Xpert MTB/RIF were calculated to be 75% (95% CI 70–80) and 98% (95% CI 97–100) respectively when compared to the CRS. The highest sensitivity was documented for lymph node specimens (90%; 95% CI 86–94), moderate sensitivity for cerebrospinal fluid (53%; 95% CI 28–79), while the sensitivity was lowest for pleural (30%; 95% CI 17–44) and peritoneal (32%; 95% CI 12–51) fluids. Xpert MTB/RIF in addition detected rifampicin resistance in 13 patients, in perfect agreement with results from the line probe assay.ConclusionsXpert MTB/RIF may be used as initial diagnostic tool for testing of lymph node specimens from patients suspected of having TB lymphadenitis. The added value of Xpert MTB/RIF to diagnose pleural or peritoneal TB is limited by its poor sensitivity.     

Improved Case Detection Using Xpert Mycobacterium tuberculosis/Rifampicin Assay in Skeletal Tuberculosis

Background: In India, musculoskeletal tuberculosis (TB) accounts for 10%–25% of extrapulmonary TB. Data on drug-resistant skeletal TB are lacking. At present, the diagnosis is based mainly on radiological techniques. Laboratory confirmation of skeletal TB is delayed as 6–8 weeks are required for culture results. Xpert Mycobacterium tuberculosis/rifampicin (MTB/RIF) assay is a fully automated test which simultaneously detects MTB and RIF resistance within 3 h. Hence, this study was done to compare the yield of case detection using Xpert assay in comparison with culture in specimens received from clinically suspected skeletal TB cases. Methods: Retrospective analysis of microscopy, culture and Xpert assay results was carried out on specimens received in laboratory from skeletal TB cases from January 2016 to December 2017. Results: Of the 201 patients analysed, majority of the specimens were obtained from the spine (55.72%). MTB was detected in 48.68% of tissue and 24% of pus specimens. Xpert assay was detected MTB in 67 (33.33%) specimens of which 53 (47.32%) were from the spine. Culture was detected MTB in 66 (32.83%) specimens. Xpert assay was detected two specimens more than culture. One specimen was positive by only culture. RIF-resistant MTB was detected in 10 (14.92%) specimens by Xpert assay. Conclusion: The spine is the most common site involved. Tissue specimen is better for early diagnosis. High RIF resistance in skeletal TB is an alarming situation. Ability of Xpert MTB/RIF assay for rapid and simultaneous detection of MTB and RIF resistance in comparison with culture makes it a useful diagnostic tool in skeletal TB.     

Diagnostic Accuracy of Xpert MTB/RIF for Extrapulmonary Tuberculosis Specimens: Establishing a Laboratory Testing Algorithm for South Africa

South Africa implemented Xpert MTB/RIF as the initial diagnostic test for pulmonary tuberculosis (TB). Xpert MTB/RIF''s accuracy for diagnosing extrapulmonary tuberculosis (EPTB) was investigated. EPTB specimens (n = 7,916) from hospitalized patients received over a 6-month period at a high-throughput TB referral laboratory in Johannesburg were investigated. Large-volume specimens were centrifuged, tissue biopsy specimens homogenized, and all specimens checked for growth of contaminating bacteria on blood agar. Contaminated samples received NALC-NaOH (N-acetyl-l-cysteine–sodium hydroxide) decontamination prior to liquid culture. Residual specimens (volumes > 1 ml) after inoculation of culture (n = 1,175) were tested using the Xpert MTB/RIF sputum protocol. Using culture as the reference, Xpert MTB/RIF''s overall sensitivity was 59% (95% confidence interval [95% CI], 53% to 65%) and specificity was 92% (CI, 90% to 94%), with the highest sensitivities of 91% (95% CI, 78% to 97%) for pus, 80% (95% CI, 56% to 94%) for lymph node aspirates, and 51% (95% CI, 44% to 58%) for fluids (ascitic, 59%; pleural, 47%). A difference in sensitivities was noticed between specimens classified as having a thick (87% [95% CI, 76% to 94%]) versus clear (watery) (48% [95% CI, 36% to 61%]) appearance. This was unchanged with traces of blood (52% [95% CI, 44% to 60%]) or precentrifugation (57% [95% CI, 28% to 82%]) among clear specimens. Xpert MTB/RIF generated an additional 124 specimen results that were contaminated by Mycobacterial Growth Indicator Tubes (MGIT; 10.5%) and diagnosed rifampin (RIF) resistance earlier (9.6% [25/260]). Xpert MTB/RIF''s performance on EPTB specimens provides very promising results and should be considered for incorporation into national TB guidelines. Xpert MTB/RIF is less affected by contaminating bacteria and reduces laboratory labor and diagnostic delay compared to traditional methods.     

Effectiveness of an integrated real-time PCR method for detection of the Mycobacterium tuberculosis complex in smear-negative extrapulmonary samples in an area of low tuberculosis prevalence

Early extrapulmonary tuberculosis (EPTB) diagnosis is particularly difficult. Among 108 smear-negative extrapulmonary samples showing a positive culture for Mycobacterium tuberculosis complex (43 body fluids and 65 nonliquid specimens), 63 (58.3%) were positive with the Xpert MTB/RIF assay (GX). GX sensitivity was quite low for samples from sterile locations (especially for pleural fluids: 26.9%) but high for some nonliquid samples, like abscess aspirates (76.5%). In summary, GX may be a useful tool to be considered for EPTB diagnosis.     

Xpert结核分枝杆菌/利福平试验对结核病及耐多药结核病诊断价值的Meta分析

目的 评估Xpert结核分枝杆菌/利福平（MTB/RIF）试验对结核病的诊断价值.方法 检索PubMed、Medline、中国知网、万方数据库等,收集Xpert MTB/RIF试验对结核病诊断价值的文献,检索起止时间均为建库至2012年6月.2名研究者独立进行资料提取和文献质量评估.采用Meta-Disc 1.4软件进行Meta分析.结果 共纳入26篇文献,其中2篇文献涉及儿童病例,包含了13 270例来自临床患者的检测标本.Meta分析结果显示,Xpert MTB/RIF试验诊断结核病的汇总敏感度为87%（95%CI：86%～88%）、特异度为97%（95%CI：97%～97%）.按照结核病的类型和患者年龄进行亚组分析,Xpert MTB/RIF试验诊断肺结核的敏感度高于肺外结核病,90%（95%CI：89%～91%） vs 76%（95%CI：72%～79%）;诊断涂阴菌阳性和涂阳菌阳性结核病的敏感度分别为74%（95%CI：71%～76%）和99%（95%CI：98%～99%）;对儿童肺结核的诊断敏感度比成人肺结核低,74%（95%CI：65%～83%） vs 90%（95%CI：89%～92%）.Xpert MTB/RIF试验诊断耐多药结核病的敏感度为96%（95%CI：94%～97%）,特异度为98%（95%CI：98%～99%）.结论 Xpert MTB/RIF试验诊断结核病的价值较高,尤其是成人结核病及耐多药结核病.Xpert MTB/RIF试验在儿童结核病中的诊断价值由于纳入文献较少,尚待进一步研究.     

Xpert MTB/RIF: a New Pillar in Diagnosis of Extrapulmonary Tuberculosis?

Approximately 10 to 15% of tuberculosis (TB) cases in India are estimated to have extrapulmonary disease, and due to a lack of diagnostic means, they often remain untreated. The early detection of Mycobacterium tuberculosis and multidrug resistance is a priority in TB diagnosis to improve the successful treatment rate of TB and reduce transmission. The Xpert MTB/RIF (Xpert) test, recently endorsed by the World Health Organization for the detection of pulmonary TB, was evaluated to test its utility in 547 patients with suspected extrapulmonary tuberculosis. Five hundred forty-seven extrapulmonary specimens were split and processed simultaneously for both culture (solid and liquid) and Xpert testing. For culture, the sensitivity was low, 53% (150/283 specimens). Xpert sensitivity and specificity results were assessed in comparison to a composite reference standard made up of smear and culture results and clinical, radiological, and histological findings. The sensitivity of the Xpert assay was 81% (228/283 specimens) (64% [89/138] for smear-negative cases and 96% [139/145] for smear-positive cases), with a specificity of 99.6%. The sensitivity was found to be high for the majority of specimen types (63 to 100%) except for cerebrospinal fluid, the sensitivity of which was 29% (2/7 specimens). The Xpert test correctly identified 98% of phenotypic rifampin (RIF)-resistant cases and 94% of phenotypic RIF-susceptible cases. Sequencing of the 6 discrepant samples resolved 3 of them, resulting in an increased specificity of 98%. In conclusion, the results of this study suggest that the Xpert test also shows good potential for the diagnosis of extrapulmonary TB and that its ease of use makes it applicable for countries where TB is endemic.     

Diagnostic performance and impact of routinely implemented Xpert® MTB/RIF assay in a setting of high incidence of drug-resistant TB in Odessa Oblast,Ukraine

Objectives and methodsThe Xpert® MTB/RIF assay (Cepheid, Sunnyvale, CA, USA) has been in routine use in Odessa Oblast, a region with the highest tuberculosis (TB) incidence in Ukraine, since 2013. We assessed the performance of the assay in routine settings and evaluated its effect on treatment outcomes.ResultsThe sensitivity of Xpert for TB detection was 93.7% (1165/1243) and 69.5% (448/645) for smear-positive and smear-negative sputum specimens, respectively, and its sensitivity for rifampicin resistance was 93.4% (1212/1298). Median time to TB detection using the Xpert assay was 0 days. Treatment initiation within 1 week increased the proportion of successful outcomes (60.1% versus 25.9%, RR = 1.86, 95%CI = 1.46–2.42), but the introduction of Xpert MTB/RIF has not led to a significant improvement in treatment outcomes (57.2% versus 46.2%; RR = 0.93, 95%CI = 0.77–1.12).ConclusionPerformance characteristics of the Xpert assay demonstrated during its routine implementation in an area of high TB and drug-resistant TB incidence in Ukraine were in line with those demonstrated in similar settings elsewhere. Rollout of rapid molecular testing may lead to better treatment results provided that it is implemented in conjunction with other programmatic improvements.     

Evaluation of the Xpert MTB/RIF test accuracy for diagnosis of tuberculosis in areas with a moderate tuberculosis burden

The Xpert MTB/RIF assay (Xpert) is a molecular assay used for direct detection of Mycobacterium tuberculosis (MTB) in clinical specimens. In this study, we aimed to assess the accuracy of the Xpert assay for the diagnosis of tuberculosis (TB) in TB suspected patients from the northern region of Iran. The obtained results were compared with the culture method. The sputum specimens were examined using the Xpert assay, smear microscopy, and solid culture media as a reference diagnostic tool. Among 293 presumptive TB cases, 92 (31.4%) were positive according to the culture method. The Xpert method detected 88 (95.7%) cases that were positive according to the culture method, compared with 78 (84.8%) positive cases according to smear microscopy. The overall sensitivity and specificity of the Xpert method for TB diagnosis were 95.7% and 99%, respectively. Also, the sensitivity and specificity for smear microscopy were 84.8% and 97.5%, respectively. The Xpert assay showed high overall sensitivity and specificity; thus, it can be effectively used for the early and accurate diagnosis of MTB in TB endemic areas. In addition, the agreement between semi‐quantitative results of Xpert and smear microscopy assays could be helpful in evaluating transmission potential in TB patients.     

Cell-free Mycobacterium tuberculosis DNA test in pleural effusion for tuberculous pleurisy: a diagnostic accuracy study

ObjectivesTuberculous pleurisy (TP) diagnosis remains difficult, with the sensitivity of Xpert MTB/RIF (Xpert) and mycobacterial culture (culture) only about 30–50%. We aimed to assess the diagnostic performance of a cell-free Mycobacterium tuberculosis DNA test (cf-TB) in pleural effusion for TP.MethodsAdults (≥18 years) with suspected TP presenting with pleural effusion were consecutively recruited, and pleural effusion specimens were prospectively collected in Beijing Chest Hospital, Beijing, China. After centrifuging pleural effusion, sediments were used for culture, Xpert and T-SPOT.TB assay, whereas supernatants were used for cf-TB and adenosine deaminase assay. The diagnostic performance was assessed against a composite reference standard.ResultsFrom June 2015 to December 2018, we prospectively evaluated 286 adults with suspected TP. One hundred twenty-two participants were classified as definite TP based on the prespecified composite reference standard. The cf-TB produced a sensitivity of 79.5% (97/122, 95% confidence interval (CI) 72.4– 86.7) for definite TP, which was superior to Xpert (38.5% (29.9–47.2); 47/122; p < 0.001) and culture (27.1% (19.2–34.9); 33/122; p < 0.001). With pleural effusion Xpert and/or culture as the reference standard, cf-TB showed 96.6% (57/59, 95% CI 92.0–100.0) sensitivity, which was also significantly higher than Xpert (79.7%, 95% CI 69.4–89.9; 47/59; p 0.004) and culture (55.9%, 95% CI: 43.3–68.6; 33/59; p < 0.001).ConclusionsThe cf-TB clearly showed improved sensitivity compared with Xpert and culture. We recommend cf-TB as the first-line test for TP diagnosis.     

Evaluation of Xpert MTB/RIF for Detection of Tuberculosis from Blood Samples of HIV-Infected Adults Confirms Mycobacterium tuberculosis Bacteremia as an Indicator of Poor Prognosis

Tuberculosis (TB) remains a leading cause of death among HIV-infected adults, in part because of delayed diagnosis and therefore delayed initiation of treatment. Recently, the Gene-Xpert platform, a rapid, PCR-based diagnostic platform, has been validated for the diagnosis of TB with sputum. We have evaluated the Xpert MTB/RIF assay for the diagnosis of Mycobacterium tuberculosis bacteremia and investigated its impact on clinical outcomes. Consecutive HIV-infected adults with fever and cough presenting to Queen Elizabeth Central Hospital, Blantyre, Malawi, were recruited and followed up for 2 months. At presentation, three sputum samples were examined by smear, culture, and Xpert MTB/RIF assay for the presence of M. tuberculosis and blood was drawn for PCR with Xpert, for mycobacterial culture (Myco/F Lytic), and for aerobic culture. One hundred four patients were recruited, and 44 (43%) were sputum culture positive for M. tuberculosis. Ten were Xpert blood positive, for a sensitivity of 21% and a specificity of 100%. The 2-week mortality rate was significantly higher among patients who were Xpert blood positive than among those who were negative (40% versus 3%; multivariate odds ratio [OR] for death if positive, 44; 95% confidence interval [CI], 3 to 662). This effect persisted on assessment of the mortality rate at 2 months (40% versus 11%; OR, 5.6; 95% CI, 1.3 to 24.6). When screening uncomplicated patients presenting with a productive cough for pulmonary TB, Xpert blood offers no diagnostic advantage over sputum testing. Despite this, Xpert blood positivity is highly predictive of early death and this test rapidly identifies a group of patients in urgent need of initiation of treatment.     

Comparison of two nucleic acid amplification assays, the Xpert MTB/RIF assay and the amplified Mycobacterium Tuberculosis Direct assay, for detection of Mycobacterium tuberculosis in respiratory and nonrespiratory specimens

We compared the performance of the Xpert MTB/RIF assay, a new real-time tuberculosis (TB) PCR test, with that of the Amplified Mycobacterium Tuberculosis Direct (MTD) assay using 162 respiratory and nonrespiratory specimens. Based on culture as the gold standard, the overall sensitivity and specificity for all sample types for the Xpert MTB/RIF assay were 90.9 and 89%, respectively, while for the MTD assay, the overall sensitivity and specificity were 97.3 and 87.1%, respectively. A higher proportion of total equivocal results were obtained for the MTD assay, at 10.5% (17/162), while the Xpert MTB/RIF assay generated 5.5% (9/162) of invalid reads.     

Evaluation of GeneXpert MTB/RIF for Diagnosis of Tuberculous Meningitis

Tuberculous meningitis (TBM) is the most severe form of tuberculosis. Microbiological confirmation is rare, and treatment is often delayed, increasing mortality and morbidity. The GeneXpert MTB/RIF test was evaluated in a large cohort of patients with suspected tuberculous meningitis. Three hundred seventy-nine patients presenting with suspected tuberculous meningitis to the Hospital for Tropical Diseases, Ho Chi Minh City, Vietnam, between 17 April 2011 and 31 December 2012 were included in the study. Cerebrospinal fluid samples were tested by Ziehl-Neelsen smear, mycobacterial growth indicator tube (MGIT) culture, and Xpert MTB/RIF. Rifampin (RIF) resistance results by Xpert were confirmed by an MTBDR-Plus line probe assay and all positive cultures were tested by phenotypic MGIT drug susceptibility testing. Overall, 182/379 included patients (48.0%) were diagnosed with tuberculous meningitis. Sensitivities of Xpert, smear, and MGIT culture among patients diagnosed with TBM were 59.3% (108/182 [95% confidence interval {CI}, 51.8 to 66.5%]), 78.6% (143/182 [95% CI, 71.9 to 84.3%]) and 66.5% (121/182 [95% CI, 59.1 to 73.3%]), respectively. There was one false-positive Xpert MTB/RIF test (99.5% specificity). Four cases of RIF resistance (4/109; 3.7%) were identified by Xpert, of which 3 were confirmed to be multidrug-resistant (MDR) TBM and one was culture negative. Xpert MTB/RIF is a rapid and specific test for the diagnosis of tuberculous meningitis. The addition of a vortexing step to sample processing increased sensitivity for confirmed TBM by 20% (P = 0.04). Meticulous examination of a smear from a large volume of cerebrospinal fluid (CSF) remains the most sensitive technique but is not practical in most laboratories. The Xpert MTB/RIF represents a significant advance in the early diagnosis of this devastating condition.     

Performance of Cepheid® Xpert MTB/RIF® and TB-Biochip® MDR in two regions of Russia with a high prevalence of drug-resistant tuberculosis

The purpose of this study was to assess the performance of Cepheid® Xpert MTB/RIF® (“Xpert”) and TB-Biochip® MDR (“TB-Biochip”). Sputum specimens from adults with presumptive tuberculosis (TB) were homogenized and split for: (1) direct Xpert and microscopy, and (2) concentration for Xpert, microscopy, culture [Lowenstein–Jensen (LJ) solid media and Mycobacteria Growth Indicator Tube® (MGIT)], indirect drug susceptibility testing (DST) using the absolute concentration method and MGIT, and TB-Biochip. In total, 109 of 238 (45.8 %) specimens were culture-positive for Mycobacterium tuberculosis complex (MTBC), and, of these, 67 isolates were rifampicin resistant (RIF-R) by phenotypic DST and 64/67 (95.5 %) were isoniazid resistant (INH-R). Compared to culture of the same specimen, a single direct Xpert was more sensitive for detecting MTBC [95.3 %, 95 % confidence interval (CI), 90.0–98.3 %] than direct (59.6 %, 95 % CI, 50.2–68.5 %) or concentrated smear (85.3 %, 95 % CI, 77.7–91.1 %) or LJ culture (80.8 %, 95 % CI, 72.4–87.5 %); the specificity was 86.0 % (95 % CI, 78.9–91.3 %). Compared with MGIT DST, Xpert correctly identified 98.2 % (95 % CI, 91.5–99.9 %) of RIF-R and 95.5 % (95 % CI, 85.8–99.2 %) of RIF-susceptible (RIF-S) specimens. In a subset of 104 specimens, the sensitivity of TB-Biochip for MTBC detection compared to culture was 97.3 % (95 % CI, 91.0–99.5 %); the specificity was 78.1 % (95 % CI, 61.5–89.9 %). TB-Biochip correctly identified 100 % (95 % CI, 94.2–100 %) of RIF-R, 94.7 % (95 % CI, 76.7–99.7 %) of RIF-S, 98.2 % (95 % CI, 91.4–99.9 %) of INH-R, and 78.6 % (95 % CI, 52.1–94.2 %) of INH-S specimens compared to MGIT DST. Xpert and Biochip were similar in accuracy for detecting MTBC and RIF resistance compared to conventional culture methods.     

Integrating the Xpert MTB/RIF Assay into a Diagnostic Workflow for Rapid Detection of Mycobacterium tuberculosis in a Low-Prevalence Area

The Xpert MTB/RIF assay is a rapid and fully automated real-time PCR assay. The performance of the Xpert MTB/RIF assay as a primary screening test for urgent clinical specimens was evaluated during a 2-year period. The results showed that replacing smear microscopy with the Xpert MTB/RIF assay facilitates laboratory handling and improves the sensitivity and specificity of Mycobacterium tuberculosis detection.     

Comparison of the Xpert MTB/RIF test with an IS6110-TaqMan real-time PCR assay for direct detection of Mycobacterium tuberculosis in respiratory and nonrespiratory specimens

The sensitivities of the Xpert MTB/RIF test and an in-house IS6110-based real-time PCR using TaqMan probes (IS6110-TaqMan assay) for the detection of Mycobacterium tuberculosis complex (MTBC) DNA were compared by use of 117 clinical specimens (97 culture positive and 20 culture negative for MTBC) that were frozen in sediment. The 97 clinical specimens included 60 respiratory and 37 nonrespiratory specimens distributed into 36 smear-positive and 61 smear-negative specimens. Among the 97 culture-positive specimens, 4 had rifampin-resistant isolates. Both methods were highly specific and exhibited excellent sensitivity (100%) with smear-positive specimens. The sensitivity of the Xpert MTB/RIF test with the whole smear-negative specimens was more reduced than that of the IS6110-TaqMan assay (48 versus 69%, P = 0.005). Both methods exhibited similar sensitivities with smear-negative respiratory specimens, but the Xpert MTB/RIF test had lower sensitivity with smear-negative nonrespiratory specimens than the IS6110-TaqMan assay (37 versus 71%, P = 0.013). Finally, the sensitivities of the Xpert MTB/RIF test and the IS6110-TaqMan assay were 79% and 84%, respectively, with respiratory specimens and 53% and 78%, respectively (P = 0.013), with nonrespiratory specimens. The Xpert MTB/RIF test correctly detected the rifampin resistance in smear-positive specimens but not in the one smear-negative specimen. The Xpert MTB/RIF test is a simple rapid method well adapted to a routine laboratory that appeared to be as sensitive as the IS6110-TaqMan assay with respiratory specimens but less sensitive with paucibacillary specimens, such as smear-negative nonrespiratory specimens.     

Use of Transrenal DNA for the Diagnosis of Extrapulmonary Tuberculosis in Children: a Case of Tubercular Otitis Media

The diagnosis of tuberculosis (TB) is difficult in children, especially for smear-negative pulmonary and extrapulmonary TB, which are common at this age. We report an 11-year-old girl with TB otitis media with negative smear microscopy and Xpert MTB/RIF but positive Mycobacterium tuberculosis-specific transrenal DNA (Tr-MTB-DNA) test results and culture for M. tuberculosis.     

Performance of Xpert MTB/RIF RUO assay and IS6110 real-time PCR for Mycobacterium tuberculosis detection in clinical samples

The Cepheid Xpert MTB/RIF research-use-only (RUO) assay and a laboratory-developed test (LDT) targeting IS6110 were evaluated and compared to mycobacterial culture as the gold standard. The performance characteristics of both molecular assays were determined by using 112 specimens from 90 patients, including 89 pulmonary specimens and 23 extrapulmonary specimens. Of the specimens tested, 37 (33%) were culture positive for the Mycobacterium tuberculosis complex; 29 were pulmonary, and 8 were extrapulmonary. Of these culture-positive specimens, 83% of the pulmonary specimens and 50% of the extrapulmonary specimens were smear positive. There was complete concordance between the smear-positive culture-positive specimens, independent of the anatomical site (100% sensitivity). The sensitivity of the MTB/RIF RUO assay for smear-negative specimens was 60% for pulmonary and 75% for extrapulmonary specimens, while the IS6110 LDT sensitivities were 40% and 0%, respectively. There was also complete concordance among the culture-negative specimens tested. Both assays showed 95% specificity, with four culture-negative specimens testing as positive. A review of patient records indicated that there was a high likelihood of the presence of M. tuberculosis complex DNA in the false-positive specimens. Biosafety analysis was performed and showed an acceptable reduction in organism viability using the processing methods described above. Both molecular assays are suitable for the detection of M. tuberculosis isolates in smear-positive pulmonary and extrapulmonary specimens, while the sensitivity of the detection of M. tuberculosis isolates in smear-negative specimens was variable.     

The rapid molecular test Xpert MTB/RIF ultra: towards improved tuberculosis diagnosis and rifampicin resistance detection

BackgroundTuberculosis diagnosis has dramatically improved since the introduction of the rapid molecular test Xpert MTB/RIF (Xpert) detecting M. tuberculosis and rifampicin resistance directly from clinical specimens, therefore shortening the turnaround time, reducing patient's isolation period and decreasing the time to start anti-TB drugs. The new version, Xpert MTB/RIF Ultra (Ultra), displays a higher sensitivity and an improved rifampicin resistance detection. Both tests have been endorsed by the World Health Organisation.AimsXpert and Ultra rapidly became widespread and paved the way for new approaches and new paradigms as well as for the development of molecular point-of-care tests (POCTs). In this narrative review, we aimed to address their performance in the diagnosis of tuberculosis and to discuss the expectations of these tests as well as their limits and the unmet needs.SourcesPeer-reviewed publications addressing the diagnostic performance of Ultra and Xpert.ContentWe focused on publications that evaluated the performance of Ultra and Xpert on the same group of patients or the same set of specimens in different tuberculosis-burden settings.ImplicationsThe studies published so far reported an increased sensitivity of Ultra when compared to Xpert, which represents a benefit for tuberculosis diagnosis. The fact that such a sensitive assay cannot distinguish between alive and dead bacilli emphasizes that caution should be exercised regarding indications and interpretation of results. Additional studies are needed to determine the true performance for the diagnosis of extrapulmonary tuberculosis because of the great diversity of the specimens.     

Evaluation of the GeneXpert MTB/RIF assay for rapid diagnosis of tuberculosis and detection of rifampin resistance in pulmonary and extrapulmonary specimens

Mycobacterium tuberculosis remains one of the most significant causes of death from an infectious agent. The rapid diagnosis of tuberculosis and detection of rifampin (RIF) resistance are essential for early disease management. The GeneXpert MTB/RIF assay is a novel integrated diagnostic device for the diagnosis of tuberculosis and rapid detection of RIF resistance in clinical specimens. We determined the performance of the MTB/RIF assay for rapid diagnosis of tuberculosis and detection of rifampin resistance in smear-positive and smear-negative pulmonary and extrapulmonary specimens obtained from possible tuberculosis patients. Two hundred fifty-three pulmonary and 176 extrapulmonary specimens obtained from 429 patients were included in the study. One hundred ten (89 culture positive and 21 culture negative for M. tuberculosis) of the 429 patients were considered to have tuberculosis. In pulmonary specimens, sensitivities were 100% (27/27) and 68.6% (24/35) for smear-positive and smear-negative specimens, respectively. It had a lower sensitivity with extrapulmonary specimens: 100% for smear-positive specimens (4/4) and 47.7% for smear-negative specimens (21/44). The test accurately detected the absence of tuberculosis in all 319 patients without tuberculosis studied. The MTB/RIF assay also detected 1 RIF-resistant specimen and 88 RIF-susceptible specimens, and the results were confirmed by drug susceptibility testing. We concluded that the MTB/RIF test is a simple method, and routine staff with minimal training can use the system. The test appeared to be as sensitive as culture with smear-positive specimens but less sensitive with smear-negative pulmonary and extrapulmonary specimens that include low numbers of bacilli.     

High diagnostic yield of tuberculosis from screening urine samples from HIV-infected patients with advanced immunodeficiency using the Xpert MTB/RIF assay

We determined the diagnostic yield of the Xpert MTB/RIF assay for tuberculosis (TB) when testing small volumes of urine from ambulatory HIV-infected patients before starting antiretroviral therapy in South Africa. Compared with a gold standard of sputum culture, the sensitivity of urine Xpert among those with CD4 cell counts of <50, 50-100, and >100 cells per microliter were 44.4%, 25.0%, and 2.7% (P = 0.001), respectively. Urine Xpert testing provides a means of rapid TB diagnosis in patients with advanced immunodeficiency and poor prognosis. These data are indicative of high rates of TB dissemination and renal involvement in this clinical population.