Comparison of Quantitative Techniques including Xpert MTB/RIF to Evaluate Mycobacterial Burden

Zyl-Smit, Richard van; Binder, Anke; Meldau, Richard; Mishra, Hridesh; Semple, Patrick; Theron, Grant; Peter, Jonny; Whitelaw, Andrew; Sharma, Suren K.; Warren, Robin M.; Bateman, Eric D.; Dheda, Keertan

doi:10.1371/journal.pone.0028815

Cited by 92 publications

(65 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…22,25 CSF centrifugation can increase the number of TB bacilli present in the given input volume inserted into the Xpert MTB/Rif cartridge (~2mL), thus making detection possible if the necessary threshold is reached. Interestingly, though MGIT culture has an analytical sensitivity threshold of ≤10 bacilli, 26 we found equivalent sensitivity (71%) compared to Xpert. It is possible that unviable bacilli detectable by PCR but not culture - with ~10–15% of participants already receiving TB treatment at screening account for cases detected by Xpert but not culture.…”

Section: Discussioncontrasting

confidence: 50%

Improved diagnostic sensitivity for tuberculous meningitis with Xpert<SUP>®</SUP> MTB/RIF of centrifuged CSF

Bahr¹,

Tugume

Rajasingham

et al. 2015

int j tuberc lung dis

109

View full text Add to dashboard Cite

Introduction TB meningitis (TBM) diagnosis is difficult and novel diagnostic methods are needed. The World Health Organization recommends Xpert MTB/RIF (Xpert) as the initial TBM diagnostic test, based on two studies reporting suboptimal sensitivity (~50–60%). Objective To study the effect of cerebrospinal fluid (CSF) centrifugation on Xpert performance for TBM detection. Design 107 predominantly HIV-infected adults with suspected meningitis were screened prospectively in Kampala, Uganda. CSF was tested by 1) microscopy for acid-fast bacilli; 2) Mycobacteria growth indicator tube culture; 3) Xpert of 2mL of unprocessed CSF; 4) Xpert of centrifuged CSF. Diagnostic performance was measured against an a priori composite reference standard of any positive CSF tuberculosis test. Results 17% (18/107) of participants had definite TBM. When CSF was centrifuged, Xpert had better sensitivity (72%, 13/18) than when using 2mL of unprocessed CSF (28%, 5/18; P=0.008). The median centrifuged CSF volume was 6mL (IQR 4–10mL). Mycobacterial culture yielded 71% (12/17) sensitivity at a median delay of 27 days. Only 39% were positive both by culture and centrifuged Xpert, with additional cases detected by Xpert and culture. Conclusions Centrifuging of CSF optimizes Xpert diagnostic performance for detection of TBM. A combination of culture and Xpert detected the largest number of cases.

show abstract

Section: Discussioncontrasting

confidence: 50%

Improved diagnostic sensitivity for tuberculous meningitis with Xpert<SUP>®</SUP> MTB/RIF of centrifuged CSF

Bahr¹,

Tugume

Rajasingham

et al. 2015

int j tuberc lung dis

109

View full text Add to dashboard Cite

show abstract

“…While commonly used sputum smear microscopy allows rapid analysis of sputum samples, it is not specific and is insensitive, with a LOD of ϳ10 4 bacilli ml Ϫ1 sputum (2). Smearnegative results require verification by bacterial culture, which has the advantage of a superior LOD, with automated liquid culture (Bactec MGIT 960; Becton Dickinson) demonstrating a detection limit of Ͻ10 organisms (25). However, culture-based methods suffer from the disadvantage of a long turnaround time (14 to 42 days) to confirm negativity in the MGIT system (Becton, Dickinson) due to the low growth rate of M. tuberculosis.…”

Section: Qualitative Methodsmentioning

confidence: 99%

Standardization of Nucleic Acid Tests for Clinical Measurements of Bacteria and Viruses

Pavšič

Devonshire²,

Parkes³

et al. 2015

J Clin Microbiol

View full text Add to dashboard Cite

f Nucleic acid-based tests for infectious diseases currently used in the clinical laboratory and in point-of-care devices are diverse. Measurement challenges associated with standardization of quantitative viral load testing are discussed in relation to human cytomegalovirus, BK virus, and Epstein-Barr virus, while the importance of defining the performance of qualitative methods is illustrated with Mycobacterium tuberculosis and influenza virus. The development of certified reference materials whose values are traceable to higher-order standards and reference measurement procedures, using, for instance, digital PCR, will further contribute to the understanding of analytical performance characteristics and promote clinical data comparability. Molecular approaches, such as nucleic acid (NA) amplification-based tests (NAATs) and sequence analysis, are increasingly replacing conventional microbiological methods, such as pathogen propagation in culture and techniques for the detection of antigens, for (i) viral load quantification, (ii) the detection of pathogenic viruses and bacteria, (iii) monitoring viral and bacterial resistance to therapeutic agents, and (iv) monitoring transmission across communities, as they often enable faster, more accurate, or more sensitive measurements (1, 2). However, commercial and in-house NAATs for infectious diseases utilize different technologies, reaction chemistries, and calibration materials, leading to demonstrable variability in the test results in terms of (i) numerical values (e.g., numbers of genome copies) for quantitative methods or (ii) presence or absence of the pathogen for qualitative methods (3-5).The In Vitro Diagnostics Directive (IVDD) in Europe has promoted assay standardization in the clinical laboratory community, through requiring manufacturers to provide information about the traceability of their calibrators (for definitions of terms in italics, see Table 1), in compliance with ISO 17511 (6). The concept of metrological traceability in clinical chemistry and laboratory medicine has been comprehensively discussed in several articles (7-9). For small-molecule measurements in clinical chemistry, such as those of blood glucose, creatinine, cortisol, and electrolytes, reference measurement procedures of high metrological quality are available which relate the quantity value of the calibrators and reference materials used in a calibration hierarchy traceable to the International System of Units (SI) as described in ISO 17511 (6, 8). However, for the majority of the more complex biomeasurements, including those based on NA testing and infectious pathogen detection, reference materials whose values are traceable to the SI and reference measurement procedures (with well-understood uncertainty) are not yet available. ISO 17511 indicates recognition of the fact that, for measurements of, for example, viral NAs (for human cytomegalovirus [CMV], human immunodeficiency virus [HIV], and hepatitis B virus [HBV]), typically WHO international standards (IS) are available, w...

show abstract

“…Additionally, Xpert MTB/RIF has approximately two-fold RESEARCH higher sensitivity than sputum smear microscopy. [10,11] For these reasons it was hoped that Xpert MTB/RIF would be a 'game-changer' for TB control. [7] However, the majority of data have been derived from ideal research conditions, and it is unclear what impact Xpert MTB/RIF has had in real-world field settings.…”

Section: Researchmentioning

confidence: 99%

Impact of Xpert MTB/RIF rollout on management of tuberculosis in a South African community

et al. 2017

View full text Add to dashboard Cite

Background. The Xpert MTB/RIF test shortens the time to microbiological confirmation of pulmonary tuberculosis (TB) under research conditions. Objective. To evaluate the field impact of Xpert MTB/RIF rollout on TB diagnostic yield and time to treatment in a South African (SA) community. Methods. We compared TB investigation outcomes for 6-month calendar periods before and after Xpert MTB/RIF rollout in a semi-rural area of SA. The proportion of adult patients who tested positive by sputum smear microscopy, liquid culture or Xpert MTB/RIF and the proportion of positive sputum smear, liquid culture or Xpert MTB/RIF tests were compared. Secondary outcomes included time to laboratory diagnosis and treatment initiation. Data were collected from the National Health Laboratory Service database and from the Western Cape Provincial Department of Health TB register. Results. Regional rollout of Xpert MTB/RIF testing occurred in 2013. Of the 15 629 patients investigated in the post-rollout period, 7.9% tested positive on GeneXpert, compared with 6.4% of the 10 741 investigated in the pre-rollout period who tested positive by sputum smear microscopy (p<0.001). Median laboratory processing time was <1 day for Xpert MTB/RIF (interquartile range (IQR) 0 -1) compared with 1 day (IQR 0 -16) for sputum smear microscopy (p=0.001). The median time to TB treatment initiation was 4 days (IQR 2 -8) after rollout compared with 5 days (IQR 2 -14) before (p=0.001). Conclusions. Patients investigated for suspected pulmonary TB were more likely to be diagnosed after rollout of Xpert MTB/RIF testing, although the benefit to diagnostic yield was modest, and Xpert MTB/RIF testing was associated with a marginal improvement in time to treatment initiation.

show abstract

Comparison of Quantitative Techniques including Xpert MTB/RIF to Evaluate Mycobacterial Burden

Cited by 92 publications

References 24 publications

Improved diagnostic sensitivity for tuberculous meningitis with Xpert<SUP>®</SUP> MTB/RIF of centrifuged CSF

Improved diagnostic sensitivity for tuberculous meningitis with Xpert<SUP>®</SUP> MTB/RIF of centrifuged CSF

Standardization of Nucleic Acid Tests for Clinical Measurements of Bacteria and Viruses

Impact of Xpert MTB/RIF rollout on management of tuberculosis in a South African community

Contact Info

Product

Resources

About