Journal.pone.0020458

Rapid and Accurate Detection of Mycobacteriumtuberculosis in Sputum Samples by Cepheid XpertMTB/RIF Assay—A Clinical Validation Study Andrea Rachow1,2*, Alimuddin Zumla3, Norbert Heinrich1, Gabriel Rojas-Ponce2, Bariki Mtafya2, KlausReither1,4, Elias N. Ntinginya2, Justin O’Grady3, Jim Huggett3, Keertan Dheda3, Catharina Boehme5, MarkPerkins5, Elmar Saathoff1, Michael Hoelscher1 1 Division of Infectious Diseases and Tropical Medicine, Medical Center of the University of Munich (LMU), Munich, Germany, 2 National Institute of Medical Research—Mbeya Medical Research Programme, Mbeya, Tanzania, 3 Department of Infection, Windeyer Institute of Medical Sciences, University College London Medical School,London, United Kingdom, 4 Swiss Tropical and Public Health Institute (Swiss TPH), Basel, Switzerland, 5 Foundation for Innovative New Diagnostics (FIND), Geneva,Switzerland Background: A crucial impediment to global tuberculosis control is the lack of an accurate, rapid diagnostic test fordetection of patients with active TB. A new, rapid diagnostic method, (Cepheid) Xpert MTB/RIF Assay, is an automatedsample preparation and real-time PCR instrument, which was shown to have good potential as an alternative to currentreference standard sputum microscopy and culture.
Methods: We performed a clinical validation study on diagnostic accuracy of the Xpert MTB/RIF Assay in a TB and HIVendemic setting. Sputum samples from 292 consecutively enrolled adults from Mbeya, Tanzania, with suspected TB weresubject to analysis by the Xpert MTB/RIF Assay. The diagnostic performance of Xpert MTB/RIF Assay was compared tostandard sputum smear microscopy and culture. Confirmed Mycobacterium tuberculosis in a positive culture was used as areference standard for TB diagnosis.
Results: Xpert MTB/RIF Assay achieved 88.4% (95%CI = 78.4% to 94.9%) sensitivity among patients with a positive cultureand 99% (95%CI = 94.7% to 100.0%) specificity in patients who had no TB. HIV status did not affect test performance in 172HIV-infected patients (58.9% of all participants). Seven additional cases (9.1% of 77) were detected by Xpert MTB/RIF Assayamong the group of patients with clinical TB who were culture negative. Within 45 sputum samples which grew non-tuberculous mycobacteria the assay’s specificity was 97.8% (95%CI = 88.2% to 99.9%).
Conclusions: The Xpert MTB/RIF Assay is a highly sensitive, specific and rapid method for diagnosing TB which has potentialto complement the current reference standard of TB diagnostics and increase its overall sensitivity. Its usefulness indetecting sputum smear and culture negative patients needs further study. Further evaluation in high burden TB and HIVareas under programmatic health care settings to ascertain applicability, cost-effectiveness, robustness and local acceptanceare required.
Citation: Rachow A, Zumla A, Heinrich N, Rojas-Ponce G, Mtafya B, et al. (2011) Rapid and Accurate Detection of Mycobacterium tuberculosis in Sputum Samplesby Cepheid Xpert MTB/RIF Assay—A Clinical Validation Study. PLoS ONE 6(6): e20458. doi:10.1371/journal.pone.0020458 Editor: Vishnu Chaturvedi, New York State Health Department and University at Albany, United States of America Received March 5, 2011; Accepted April 21, 2011; Published June 29, 2011 Copyright: ß 2011 Rachow et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permitsunrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Funding: This study was funded by the European Commission (E.C.), DG Research, (LSHP-CT-2006-037785), EC.AIDCO, (ADAT SANTE/2006/129-931), and by theGerman Ministry for Education and Research (BmBF). MH, AZ, JH, JO and KD receive support from the EU-FW7, EDCTP, UK-MRC, and the EU FW7. AZ receivessupport from the NIHR, UCLH-CBRC. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing Interests: The authors have no financial conflict of interest. No commercial partner was involved in the study or the writing of the manuscript.
active TB, especially in TB and HIV endemic areas are eithertreated based on clinical grounds and without microbiological Tuberculosis (TB) continues to kill 1.8 million people annually.
proof of TB-infection or remain undiagnosed and are continuing Progress towards global TB control has remained elusive despite to spread the disease in the community [3]. The need for a more intensified standard measures of TB control [1]. National TB accurate, point-of-care TB diagnostic test that is applicable in TB control programmes in most TB and TB/HIV endemic countries and HIV endemic areas is crucial for achieving global TB control.
continue to rely largely on century old, antiquated and inaccurate Modeling studies show that new diagnostics for TB and multi-drug tools such as direct smear microscopy, solid culture, chest resistant TB (MDR-TB) may have an important impact at the radiography and tuberculin skin testing [2]. Currently, there is population level in disease endemic countries [4]. Over the past no rapid, point-of-care test that allows early detection of active TB decade the TB diagnostics pipeline has expanded, with several at the peripheral health clinic level. Thus many patients with technologies showing promise [2]. Among them are new and Detection of Tuberculosis by Xpert MTB/RIF Assay simplified PCR-based methods which have been shown to detect and HIV pre- and post-test counseling of participants. Eight Mycobacterium tuberculosis (Mtb) and resistance to rifampicin with patients were excluded from the study because they either were good sensitivity and specificity directly from positive cultures or incapable to produce sputum at recruitment or were lost to follow clinical specimens. Current large-scale roll-out of liquid culture promises to improve sensitivity and drug susceptibility testing(DST). However, caution should be applied in settings where non- tuberculous mycobacteria (NTM) are common environmental All 292 study patients had three sputum samples collected (one microorganisms, such as in sub-Saharan Africa [5,6] because spot sample, one morning sample and another spot sample, detection of NTM growth could lead to a false diagnosis of TB.
making a total of three for analyses).
The World Health Organization (WHO) is ensuring that new TB diagnostic policies are evidence-based [7], and in alignment with the GRADE approach to guideline development [8]. In 2009, the first Sputum samples were split into two aliquots, one of which was technical data were announced from an automated molecular test stored at 280uC. The other aliquot was processed for standard for TB, the Xpert MTB/RIF Assay co-developed by the Foundation sputum microscopy after Ziehl-Neelsen staining and culture. Sputa for Innovative New Diagnostics, Cepheid (Sunnyvale, Calif, USA), were decontaminated by the NALC-NaOH method and the and the University of Medicine and Dentistry of New Jersey [9]. This resulting pellet was examined for acid fast bacilli (AFB) by assay, which was CE (Conformite´ Europe´enne) marked in 2009, microscopy and culture, always both on Lowenstein-Jensen media avoids many of the pitfalls of conventional nucleic acid amplification (LJ) and BACTEC MGIT (MGIT) 960 liquid culture (BAC- tests and can be performed by staff with minimal training, and used TECTM MGIT, Becton Dickinson, Sparks, USA) in parallel, using for case detection or MDR screening at the same time. Thus this standard protocols. The AFB smear grade was defined following assay is said to specifically detect Mtb and rifampicin resistance from the International Union against Tuberculosis and Lung Disease one sputum sample within 2 hours. It is said to constitute a greatly scale: Scanty (1–9/100 fields), 1+(10–99/100 fields), 2+(1–10/100 simplified nucleic acid amplification test which can be performed by fields) and 3+(.10/field) [15]. A patient was considered smear any laboratory or clinical personnel after minimal introductive positive if at least one smear was graded scanty or higher. Species training [9]. The Xpert MTB/RIF Assay is a single-use sample determination of cultured organisms was performed by GenotypeH processing cartridge system that holds all required sample Mycobacterium MTBC, CM and AS tests (Hain Lifescience, preparation and real-time PCR reagents and hosts the whole PCR Nehren, Germany). Rifampicin susceptibility was tested using reaction. The assay has recently undergone performance evaluation SIRE test kits in the BACTEC MGIT system [16].
on respiratory specimens [9,10,11,12] as well as on non-respiratory The microbiology and the molecular biology laboratory of samples [11] [13], one of them was a multi-country ‘technical’ NIMR-Mbeya Medical Research Programme operate in accor- evaluation which showed the Xpert MTB/RIF Assay to have high dance with standardized protocols and quality control and quality sensitivity and specificity [10], producing results in 2 hours. Since December 2010 WHO recommends the use of Xpert MTB/RIFAssay as initial diagnostic test for TB diagnosis in patients with suspected MDR-TB or TB in association with HIV- infection [14].
Participants were classified into 5 groups according to their In this cohort- study we wanted to validate the diagnostic accuracy of microbiological, radiological and clinical findings at enrollment the Xpert MTB/RIF Assay in our setting, an area with high prevalence of TB and HIV. We compared the results of the Xpert Patients with microbiologically confirmed MTB/RIF Assay to sputum smear and culture as standard pulmonary TB who had at least one positive sputum-smear (S+) diagnostic methods on samples from HIV-infected and HIV- and one Mtb-positive sputum culture (C+) sample.
uninfected patients with suspected TB, from Mbeya, Tanzania.
Patients with microbiologically confirmed pulmonary TB who were smear-negative but had at least one Patients with bacterial chest infection who were sputum smear- and culture-negative and responded to antibiotic The study was approved by the local Mbeya Medical Research treatment with amoxicillin, co-trimoxazole, or cefpodoxime with and Ethics Committee and the National Institute of Medical full recovery. No anti-TB treatment was given to these patients.
Research (NIMR) Ethics Committee. Written informed consent was obtained from all participants or their legal representative for pulmonary TB (despite lacking microbiological confirmation of use of their sputum for TB diagnostics research.
Mtb) based on clinical and radiologic findings after failure torespond to two courses of oral antibiotics comprising amoxicillin, co-trimoxazole, or cefpodoxime. All patients showed a clear The study was conducted according to the principles expressed clinical response to TB treatment in the follow-up.
in the Declaration of Helsinki as revised in 2000 at the Mbeya Patients, who were lost to clinical follow up Referral Hospital in the Mbeya region, south west Tanzania which or had no complete set of data (either culture results or radiological data were unavailable). No anti-TB treatment was accorded.
Three hundred consecutive patients with symptoms suggestive All 292 patients were followed up for a period of 56 days. TB of pulmonary TB who presented to the Mbeya Referral Hospital drug treatment was accorded by the District Leprosy and TB between July 2007 and September 2007 were interviewed for Coordinator following Tanzanian national guidelines for TB enrolment into the study. After informed consent, recruitment treatment. Patients diagnosed with HIV infection were referred for procedures comprised interviews regarding medical history, further staging and treatment to the relevant Care and Treatment clinical examination, chest radiography, blood sample collection Detection of Tuberculosis by Xpert MTB/RIF Assay Analysis of sputum samples by Xpert MTB/RIF Assay 69 (23.6% of 292) patients had microbiologically confirmed Biobanked sputum samples from 292 patients of all study groups pulmonary TB with Mtb identified in their sputum culture. These were subject to analysis using Xpert MTB/RIF Assay during the included 51 sputum smear-positive (S+/C+) and 18 smear- period January 2010 to March 2010 at the same TB laboratory at negative (S2/C+) cases. 103 patients (35.3% of 292) were shown MMRP. Clinical and laboratory staff involved with this study were to have no TB (C2). These patients were smear and culture blinded for clinical diagnosis, sputum smear, culture and drug negative and showed a sustained recovery within 56 days of susceptibility results of the sputa samples. Frozen sputa were receiving antibacterial antibiotic therapy. Out of the remaining thawed and processed according to the Xpert MTB/RIF Assay 120 patients, 77 (26.4% of 292) were classified as clinical TB-cases test procedure [9]. Positive results were displayed by Xpert MTB/ (C2) on clinical and radiological grounds although sputum culture RIF Assay as semi-quantitative estimates depending on the Ct results were negative for Mtb. All patients in this group received value of the present sample. Lower cycle threshold (Ct) values anti- TB treatment and showed a sustained recovery after 56 days.
represented a higher concentration of Mtb complex (MTBC) DNA Two study participants were smear-positive but culture- negative.
and higher Ct values represented a lower DNA-concentration. A These patients were included into this group due to typical clinical Ct value of $40 reflected a Mtb- negative sample.
and radiological findings as well as marked improvement underanti 2TB therapy. 43 participants (14.7% of 292) were classified as indeterminate and not included in the final analysis since there For statistical comparison, Mtb culture positivity was used as was no clear evidence of mycobacterial or other bacterial infection reference standard, defined as identification of Mtb in at least one in those patients or sufficient data were not available for positive standard sputum culture (either on LJ slopes or MGIT classification into one of the other groups.
culture) out of three analysed sputum samples. Statistical analysisby number or type of sputum samples used by test performed was run using Stata 11.0 statistics software (Statacorp, College Station, The overall HIV prevalence in the study population was 58.9% TX, USA) [17]. Sensitivity and specificity were calculated using (95%CI = 45% to 89.9%). In microbiologically confirmed TB Stata’s ‘‘diagt’’ component. Associations of indicators of AFB cases the HIV prevalence (66.7%) in group (S+/C+) was not density between Xpert MTB/RIF Assay, sputum smear micros- statistically different (p-value 0.07) from HIV prevalence (88.9%) copy and culture results were assessed using linear regression and Diagnostic performance analysis of the Xpert MTB/RIF In table 1 the results of Xpert MTB/RIF Assay as per patient analysis are depicted according to the patient classification group.
All sample results were obtained within two hours of 50 out of 51 smear and culture positive patients (S+/C+) were commencing the analyses. There were no technical operational detected positive by Xpert MTB/RIF assay resulting in a 98% problems encountered with the use of the machine that required sensitivity (98% CI = 89.6% to 100.0%) in this group. Only 11 out of 18 patients with a negative smear and positive culture (S2/C+)were positive by the assay. Sensitivity was 61.1% (CI = 35.7% to 82.7%) in this group which is statistically different (p-value,0.001) A total of 292 individuals (151 females and 141 males) with a to the sensitivity of the assay (98%) in group (S+/C+). Among all mean age of 39.2 years (SD = 13.8) were classified into five 103 TB-negative patients (C2) the submitted sputa of one patient different groups according to microbiological, radiological and were Xpert MTB/RIF Assay positive, giving the assay a specificity of 99% ( 95%CI = 94.7% to 100.0%). The corresponding patient Table 1. Patient classification, HIV prevalence and Xpert MTB/RIF Assay results for each patient group.
a = Xpert MTB/RIF Assay result per patient analysis.
b = sensitivity in this group, 95%CI = 89.6% to 100.0%.
c = sensitivity in this group, 95%CI = 35.7% to 82.7%.
d = specificity in this group, 95%CI = 94.7% to 100.0%.
S+/C+ = sputum smear positive and culture positive; S2/C+ = sputum smear negative and culture positive; C2 = culture negative.
doi:10.1371/journal.pone.0020458.t001 Detection of Tuberculosis by Xpert MTB/RIF Assay was HIV-infected and had a previous history of TB and of Diagnostic performance of the Xpert MTB/RIF Assay in per sample analysis and compared to other tests Amongst the 77 participants in the group of Clinical TB (C2) For all 69 culture positive TB patients (S+/C+ and S2/C+), who had no Mtb- positive sputum culture but a clinical diagnosis of and 103 patients defined as TB negative (No TB [C2]), the TB, the Xpert MTB/RIF Assay detected an additional seven diagnostic performance per sample (first spot sample and morning (9.1% of 77) Mtb- positive patient samples. The Ct-values sample) of all the diagnostic tests alone and their combination were displayed by GeneXpert for these samples were high (Ct 22–28) ascertained; the data is presented in table 2. The reference or very high (Ct.28), indicating a low mycobacterial load in the standard, on which microbiological confirmed TB diagnosis was sputum. Despite the low amplification signal, Xpert MTB/RIF based in this study, was defined as at least one positive sputum Assay was consistently positive in the analysis of single or multiple culture for Mtb out of three sputum samples analysed. Compared sputum samples from these seven patients. All seven patients were to spot sputa the sensitivity of the Xpert MTB/RIF Assay was only HIV-positive and were thus treated for TB based on their clinical slightly increased in morning sputa showing no statistical and radiological findings and non-responsiveness to anti-bacterial difference (p-value 0.459); 84.1% (95%CI = 73.3% to 91.8%) vs.
antibiotic therapy. None of them had a history of previous TB 88.4% (95%CI = 78.4% to 94.9%). Importantly, the overall per diagnosis or treatment. The sputum samples of the remaining 70 patient sensitivity of 88.4% (95%CI = 78.4% to 94.9%) of the (90.9% of 77) participants of this group were Xpert MTB/RIF Xpert MTB/RIF Assay remained the same when three sputa (first spot sample, morning sample and 2nd spot sample) were analysed.
Table 2. Comparison of Xpert MTB/RIF Assay and other methods with reference standard for both HIV-positive and -negativeparticipants.
aall culture results include speciation test results (for confirmation of Mtb or exclusion of Mtb in case when NTM present).
breference standard for confirmed TB- diagnosis, defined as at least one positive culture (LJ or Mgit) confirmed as Mtb in speciation of per patient analysis; Mtb- negative defined as all cultures negative (LJ and Mgit) for Mtb in per patient analysis, speciation results included.
Smear = Sputum smear microscopy after ZN-staining; LJ = Loewenstein-Jensen culture on solid media; Mgit = BACTEC MGIT 960 liquid culture.
doi:10.1371/journal.pone.0020458.t002 Detection of Tuberculosis by Xpert MTB/RIF Assay In both types of sputa sensitivity of Xpert MTB/RIF Assay was (expressed in Cycle threshold (Ct) values - which correlate always higher than that of any other method alone.
inversely with the concentration of target DNA) (figure 1, 2).
Specificity of Xpert MTB/RIF Assay was the same in spot and morning sputum (99%, 95%CI = 94.7% to 100.0%).
Specificity of Xpert MTB/RIF Assay in NTM - positive For analysis of 50 HIV-infected patients with a positive TB culture (S+/C+ and S2/C+) and 50 HIV-infected patients from There were 45 patients (15.4% of 292), 24 in the No-TB (C2) the No TB (C2) group, the diagnostic results of the same tests as group and 21 in the group of Clinical TB (C2), in whose cultures above are shown in table 3. In spot sputum the Xpert MTB/RIF grew NTM. The speciation tests of these NTM detected M.
Assay had 82% (95%CI = 68.6% to 91.4%) sensitivity compared fortuitum (10), M. intracellulare (5), M. celatum I+II (2), M.
to 88% (95%CI = 75.7% to 95.5%) sensitivity in morning sputum scrofulaceum (1) and M. szulgai (1). In 32 cases a final which was statistically not different (p-value 0.864). In both types identification of the NTM was not possible. Only one of these of sputa specificity was 98% (95%CI = 89.4% to 100.0%).
patients’ sputum samples tested positive by Xpert MTB/RIFAssay, resulting in an Xpert MTB/RIF Assay specificity of 97.8% in this group (95%CI = 88.2% to 99.9%).
An analysis of markers for sputum bacterial load, such as grade of smear- positivity (figure 1) and time to positivity in MGIT liquid culture (figure 2), shows good correlation with the quantitative All strains of Mtb isolated were drug sensitive. There were no result of real-time PCR obtained from the Xpert MTB/RIF Assay Mtb strains resistant to RIF or INH when tested by standard drug Table 3. Comparison of Xpert MTB/RIF Assay and other methods with reference standard in HIV-positives only.
aall culture results include speciation test results (for confirmation of Mtb or exclusion of Mtb in case when NTM present).
breference standard for confirmed TB- diagnosis, defined as at least one positive culture (LJ or Mgit) confirmed as Mtb in speciation of per patient analysis; Mtb- negative defined as all cultures negative (LJ and Mgit) for Mtb in per patient analysis, speciation results included.
Smear = Sputum smear microscopy after ZN-staining; LJ = Loewenstein-Jensen culture on solid media; Mgit = BACTEC MGIT 960 liquid culture.
doi:10.1371/journal.pone.0020458.t003 Detection of Tuberculosis by Xpert MTB/RIF Assay patients who were sputum Mtb culture negative and were classifiedas having ‘Clinical TB’. Finally, the assay was easy to perform,gave results within two hours of sample processing, and there wereno operational difficulties during its usage.
Our data validate and support the findings of a technical evaluation of the Xpert MTB/RIF Assay by Helb et al. [9] and amulticenter assessment at five trial sites in Peru, Azerbaijan, SouthAfrica (Cape Town and Durban) and India by Boehme et al. [10].
While the sensitivity for smear positive samples was nearly 100%in all three studies, our analysis showed a substantially lowersensitivity in smear negative, culture positive samples than the twoprevious studies (71% Helb et al., 90% Boehme et al. and 61% inour study). Those differences might be explained by the followingaspects: The previous studies included samples under much moreselective conditions than our study which used samples fromsequential patients with suspected TB without any pre-selection.
Our study used concentrated sputum samples (which has been Figure 1. Cycle threshold (Ct-value) versus grade of smear- reported to increase sensitivity of smear microscopy by up to 39% positivity. Ct versus degree of smear positivity, coded as negative = 0,scanty = 1, 1+ = 2 etc (regression coefficient b = 25.02, 95%CI = 27.44 to [18]) and applied the revised WHO recommendation where one 22.60). Ct for Xpert MTB/RIF Assay negatives was coded as 40.
single scanty sputum (1–9/100 fields) defines a smear positive patient. The study from Boehme et al. [10] was performed onfresh sputum samples, while we used frozen samples. However, sensitivity testing (DST) methods on liquid culture. There was also there is a controversy on whether the freezing process may cause no RIF resistance detected in any of the sputum samples processed some degradation of DNA or as discussed by Helb et al. [9] and Marlowe et al. [12] increases viscosity of the sample with improvesrecovery of mycobacterial nucleic acids.
TB-control, especially in TB/HIV-endemic areas with poor resources, is hampered by a lack of sensitivity and specificity of Our study has several important and novel findings: Firstly, this sputum smear microscopy which is often the only diagnostic method is a relatively large, controlled, comprehensive clinical validation in place. In December 2010, WHO endorsed the Xpert MTB/RIF- study of the diagnostic accuracy of the Xpert MTB/RIF assay in a Assay for widespread use. Among other indications the assay has a clinical cohort of patients suspected of having active TB from a TB strong recommendation as initial diagnostic test in individuals with and HIV endemic area. More than 58% of the included subjects suspected HIV-associated TB [14]. HIV-infected patients are were HIV-infected. Secondly, we present data showing that Xpert known to tend to have smear- negative sputum samples. This could MTB/RIF Assay has a very high sensitivity and specificity when be confirmed by our data showing that 88.9% of TB patients with a tested in the field compared to the current reference standard.
negative smear were HIV-infected. In this study we provide promise Thirdly, our data suggests that HIV status of patients does not that the Xpert MTB/RIF Assay has a high diagnostic accuracy in affect the performance of Xpert MTB/RIF Assay. Fourthly, Xpert HIV-positive patients (table 3) and that its performance is similar to MTB/RIF Assay is very specific and is able to distinguish NTM that in HIV-negative patients in our cohort.
from Mtb. Fifthly, Xpert MTB/RIF Assay was positive in seven In terms of specificity, we found potentially false positive sputa from two patients detected by Xpert MTB/RIF Assay. One was apatient from group ‘‘No TB’’ (C2) whose samples were testedpositive by Xpert MTB/RIF Assay. The fact that all three sputumsamples obtained from that patient were consistently positive inthe Xpert MTB/RIF Assay makes contamination an unlikelyexplanation. Furthermore, the patient had a history of previousTB, suggesting a sub clinical relapse or excretion of residualpersistent DNA from dead organisms, as possible reasons for thepositive result. The latter has been suggested to occur in treatedTB patients [19]. The other false positive sputum sample was froma patient in the group ‘‘Clinical TB’’ (C2) who had NTM insputum culture. Mtb was later also confirmed by additional HainMTBDRplusH testing, which has a high specificity in clinical sputa[20,21], and requires detection of katG and inhA amplification inaddition to rpoB [22]. Therefore, non-specific amplification by theXpert MTB/RIF Assay can be excluded. There was no history ofprevious TB, but the patient presented in an advanced stage of HIV immunosuppression (37 CD4 T-cells/ml). It is possible thatconcomitant infection or colonization with Mycobacterium fortuitum Figure 2. Cycle threshold (Ct-value) versus time to positivity in which was detected in this patient’s culture inhibited the slower MGIT liquid culture. Ct versus days from inoculation into MGIT liquid growth of Mtb in culture, thereby preventing detection of the culture to culture positivity as reported by the MGIT instrument patient’s TB by standard methods. If the reasoning in both these (b = 1.19, 95%CI = 0.98 to 1.39). Ct for Xpert MTB/RIF Assay negativeswas coded as 40.
cases is assumed as correct, the specificity of Xpert MTB/RIF Detection of Tuberculosis by Xpert MTB/RIF Assay Notwithstanding these exceptions, we are demonstrating here compared to 84.2% (95%CI = 74.0% to 91.6%) and 79.0% for the first time that Xpert MTB/RIF Assay can accurately (95%CI = 68.1% to 87.5%) respectively for all other methods differentiate between Mtb and NTM in clinical samples. This is combined (smear plus solid and liquid culture), (data not shown).
relevant since NTM are commonly found in large geographical For future clinical practice, it is however of paramount regions of Sub-Saharan Africa and are often picked up in sputum importance to ascertain that these patients detected by Xpert cultures, especially MGIT liquid cultures. Approximately one MTB/RIF Assay only are unambiguously true TB cases that were third of positive sputum cultures yield NTM in our setting in missed by sputum culture and therefore a more thorough clinical Mbeya, Tanzania. In our experience, these NTM are rather evaluation study which specifically addresses these cases would be representing clinically insignificant concomitant flora of the warranted. Furthermore, it will also be necessary to explore how sputum or saliva and are rarely causing disease in neither this new, promising assay can be made accessible to developing immunosuppressed nor immunocompetent individuals. Of 45 countries. As with any new diagnostic test, the impact of Xpert patients with NTM that were found in the groups of No TB (C2) MTB/RIF Assay will depend on the reproducibility of the results and Clinical TB (C2), one patient tested positive by Xpert MTB/ under actual field conditions, the manner and extent of their RIF Assay, resulting in a Xpert MTB/RIF Assay specificity of introduction, the strength of the laboratories and the degree to 97.8%. As described above there is good evidence to believe that which access to appropriate therapy follows access to diagnosis.
this case was a true TB case. Recent analytical studies with NTM Our data suggest that especially smear-negative TB patients could isolates by Helb et al. [9] and Blakemore et al. [23] indicated benefit from the new assay in those areas where no culture is specificity of 100% for the Xpert MTB/RIF Assay, however, in a available. Both aspects, that analysis of only one single spot sputum sample by Xpert MTB/RIF-Assay can already reach reasonable In our study Xpert MTB/RIF Assay detected seven TB cases sensitivity and that the result would be available on the day of (9,1%) in the group of patients with Clinical TB (C2) which were sputum collection could result into more patients with active TB not picked up by any of the standard methods. Also, in the study being diagnosed, avoiding loss of patients and treatment delay in by Boehme et al. [10] 29,3% of patients were classified as clinical those TB-suspects with a negative smear result who would TB cases who had no positive culture for Mtb but had a positive undergo two ineffective empirical courses of antibiotics before Xpert MTB/RIF Assay result. Unfortunately these cases were not TB-treatment would be initiated. Finally, this new sensitive and delivered to final analysis. In our study these cases were followed rapid diagnostic assay could lead to the reduction of the infectious over 56 days and we are confident based on the clinical evidence pool and improvements in TB control.
and the positive response to anti-TB treatment that they were trueTB cases, even if the final bacteriological proof is missing.
Because of the difficulty that an imperfect reference standard poses when newer tests are evaluated that might be better than the The authors thank all staff at the TB clinic and the laboratories at NIMR- reference standard, we suggest to introduce the term, ‘‘extended’’ MMRP, Mbeya, Tanzania, for their dedicated work, as well as the patients reference standard to enable an alternative comparison of new and who agreed to participate in this study.
established assays. For our data the ‘extended’ reference standardwould include as TB-positives those cases with a positive smear or culture and the seven Xpert MTB/RIF Assay positive cases with Conceived and designed the experiments: AR NH KR ES MH JH.
reasonable clinical evidence of active TB. If this definition was Performed the experiments: AR GR-P BM KR ENN. Analyzed the data: used the Xpert MTB/RIF Assay would have a higher or equal AR AZ ES MH. Contributed reagents/materials/analysis tools: CB MP sensitivity in each per sample analysis than any of the standard ES JO KD. Wrote the paper: AR AZ NH KR ES MH. Critical appraisal methods alone or in combination. Thus sensitivity of Xpert MTB/ of the manuscript: AR AZ NH GR-P BM KR ENN JO JH KD CB MP ES RIF Assay would be 84.2% (95%CI = 74.0% to 91.6%) in one spot MH. Finalized the manuscript: AR AZ MH.
and 86.8% (95%CI = 77.1% to 93.5%) in one morning sputum 1. WHO (2010) WHO Report. World Health Organization. M/XDR-TB 10. Boehme CC, Nabeta P, Hillemann D, Nicol MP, Shenai S, et al. (2010) Rapid Surveillance and Control: 2010 Global Update. Geneva, Switzerland, 2010.
molecular detection of tuberculosis and rifampin resistance. N Engl J Med 363: 2. Wallis RS, Pai M, Menzies D, Doherty TM, Walzl G, et al. (2010) Biomarkers and diagnostics for tuberculosis: progress, needs, and translation into practice.
11. Moure R, Munoz L, Torres M, Santin M, Martin R, et al. (2010) Rapid Detection of Mycobacterium tuberculosis complex and Rifampin Resistance in 3. Harries AD, Zachariah R, Corbett EL, Lawn SD, Santos-Filho ET, et al. (2010) Smear-negative Clinical Samples using an Integrated Real Time PCR Method.
The HIV-associated tuberculosis epidemic–when will we act? Lancet 375: 12. Marlowe EM, Novak Weekley SM, Cumpio J, Sharp SE, Momeny MA, et al.
4. Dowdy DW, Lourenco MC, Cavalcante SC, Saraceni V, King B, et al. (2008) (2011) Evaluation of the Cepheid Xpert MTB/RIF assay for the Direct Impact and cost-effectiveness of culture for diagnosis of tuberculosis in HIV- Detection of Mycobacterium tuberculosis Complex from Respiratory Speci- infected Brazilian adults. PLoS One 3: e4057.
5. Chilima BZ, Clark IM, Floyd S, Fine PE, Hirsch PR (2006) Distribution of 13. Hillemann D, Ruesch-Gerdes S, Boehme C, Richter E (2011) Rapid molecular environmental mycobacteria in Karonga District, northern Malawi. Appl detection of extrapulmonary tuberculosis by automated GeneXpert(R) MTB/ 6. Buijtels PC, van der Sande MA, Parkinson S, Verbrugh HA, Petit PL, et al.
14. WHO (2010) Available: http://www.who.int/tb/laboratory/roadmap_ (2010) Isolation of non-tuberculous mycobacteria at three rural settings in Zambia; a pilot study. Clin Microbiol Infect 16: 1142–1148.
15. Van Rie A, Fitzgerald D, Kabuya G, Van Deun A, Tabala M, et al. (2008) 7. WHO (2008) World Health Organization. Moving research findings into new Sputum smear microscopy: evaluation of impact of training, microscope WHO policies. Available: http://www.who.int/tb/dots/laboratory/policy/en/ distribution, and use of external quality assessment guidelines for resource-poor index4.html. Geneva: World Health Organization.
settings. J Clin Microbiol 46: 897–901.
8. Pai M, Ramsay A, O’Brien R (2008) Evidence-based tuberculosis diagnosis.
16. Scarparo C, Ricordi P, Ruggiero G, Piccoli P (2004) Evaluation of the fully automated BACTEC MGIT 960 system for testing susceptibility of Mycobac- 9. Helb D, Jones M, Story E, Boehme C, Wallace E, et al. (2010) Rapid detection terium tuberculosis to pyrazinamide, streptomycin, isoniazid, rifampin, and of Mycobacterium tuberculosis and rifampin resistance by use of on-demand, ethambutol and comparison with the radiometric BACTEC 460TB method.
near-patient technology. J Clin Microbiol 48: 229–237.
Detection of Tuberculosis by Xpert MTB/RIF Assay 17. Stata website. Available: http://www.stata.com/ (accessed 2010 Aug 7).
Mycobacterium tuberculosis strains and clinical specimens. J Clin Microbiol 18. Steingart KR, Ng V, Henry M, Hopewell PC, Ramsay A, et al. (2006) Sputum processing methods to improve the sensitivity of smear microscopy for 21. Ling DI, Zwerling AA, Pai M (2008) GenoType MTBDR assays for the tuberculosis: a systematic review. Lancet Infect Dis 6: 664–674.
diagnosis of multidrug-resistant tuberculosis: a meta-analysis. Eur Respir J 32: 19. Wang JY, Lee LN, Chou CS, Huang CY, Wang SK, et al. (2004) Performance assessment of a nested-PCR assay (the RAPID BAP-MTB) and the BD 22. Richter E, Rusch-Gerdes S, Hillemann D (2009) Drug-susceptibility testing in ProbeTec ET system for detection of Mycobacterium tuberculosis in clinical TB: current status and future prospects. Expert Rev Respir Med 3: 497–510.
specimens. J Clin Microbiol 42: 4599–4603.
23. Blakemore R, Story E, Helb D, Kop J, Banada P, et al. (2010) Evaluation of the 20. Hillemann D, Rusch-Gerdes S, Richter E (2007) Evaluation of the GenoType analytical performance of the Xpert MTB/RIF assay. J Clin Microbiol 48: MTBDRplus assay for rifampin and isoniazid susceptibility testing of

Source: http://www.fundacaoataulphodepaiva.com.br/2013/03/Validation-PLoS-Med-2011.pdf