Diagnosing Xpert MTB/RIF negative TB: Impact and cost of alternative algorithms for South Africa

Schnippel, Kathryn; Meyer‐Rath, Gesine; Long, Lawrence; Stevens, Wendy; Sanne, Ian; Rosen, Sydney

doi:10.7196/samj.6182

Cited by 28 publications

(30 citation statements)

References 13 publications

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“…Similarly, Xpert-negative cases in our report were more likely to have CD4 cell count more than 100 cells/µL, but despite having longer median time to culture positive (28 days compared to 21 days of Xpert-positive cases), the difference was not statistically significant (p=0.28). To examine this issue further, an analysis of the impact and cost of alternative diagnostic algorithms in a high TB/HIV co-infection setting projected that the addition of a second Xpert test (Xpert/Xpert) performs similarly but less expensively than the addition of culture (Xpert/culture) [47], while chest radiography performed well as a ruling-out, rather than rule-in, tool among Xpert-negative TB cases [48]. Empiric data supporting these assertions, however, are lacking.…”

Section: Discussionmentioning

confidence: 99%

The Diagnostic Performance of a Single GeneXpert MTB/RIF Assay in an Intensified Tuberculosis Case Finding Survey among HIV-Infected Prisoners in Malaysia

Al-Darraji

Razak

et al. 2013

PLoS ONE

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BackgroundDelays in tuberculosis (TB) diagnosis, particularly in prisons, is associated with detrimental outcomes. The new GeneXpert MTB/RIF assay (Xpert) offers accurate and rapid diagnosis of active TB, but its performance in improving case detection in high-transmission congregate settings has yet to be evaluated. We assessed the diagnostic accuracy of a single Xpert assay in an intensified case finding survey among HIV-infected prisoners in Malaysia.MethodsHIV-infected prisoners at a single site provided two early-morning sputum specimens to be examined using fluorescence smear microscopy, BACTEC MGIT 960 liquid culture and a single Xpert. The sensitivity, specificity, negative and positive predictive values of Xpert were calculated relative to gold-standard results using MGIT 960 liquid culture. Relevant clinical and demographic data were used to examine correlates of active TB disease.ResultsThe majority of enrolled subjects with complete data (N=125) were men (90.4%), age <40 years (61.6%) and had injected drugs (75.2%). Median CD4 lymphocyte count was 337 cells/µL (IQR 149-492); only 19 (15.2%) were receiving antiretroviral therapy. Of 15 culture-positive TB cases, single Xpert assay accurately detected only eight previously undiagnosed TB cases, resulting in a sensitivity, specificity, positive predictive value and negative predictive value of 53.3% (95% CI 30.12-75.2%), 100% (95% CI 96.6-100%), 100% (95% CI 67.56-100%) and 94.0% (95% CI 88.2-97.1%), respectively. Only 1 of 15 (6.7%) active TB cases was smear-positive. The prevalence (12%) of undiagnosed active pulmonary TB (15 of 125 prisoners) was high and associated with longer duration of drug use (AOR 1.14, 95% CI 1.03-1.26, for each year of drug use).ConclusionsSingle Xpert assay improved TB case detection and outperformed AFB smear microscopy, but yielded low screening sensitivity. Further examination of the impact of HIV infection on the diagnostic performance of the new assay alongside other screening methods in correctional settings is warranted.

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Section: Discussionmentioning

confidence: 99%

The Diagnostic Performance of a Single GeneXpert MTB/RIF Assay in an Intensified Tuberculosis Case Finding Survey among HIV-Infected Prisoners in Malaysia

Al-Darraji

Razak

et al. 2013

PLoS ONE

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“…For example, a modelling evaluation of Xpert scale-up across southern Africa 18 is unlikely to provide useful guidance on where to place Xpert machines in the USA, 44 or whether to supplant other funds to pay for Xpert testing. 45,46 …”

Section: The Challenges Of Using Models and Approaches To Addressimentioning

confidence: 99%

Bridging the gap between evidence and policy for infectious diseases: How models can aid public health decision-making

Knight

Dharan

Fox

et al. 2016

International Journal of Infectious Diseases

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SUMMARYThe dominant approach to decision-making in public health policy for infectious diseases relies heavily on expert opinion, which often applies empirical evidence to policy questions in a manner that is neither systematic nor transparent. Although systematic reviews are frequently commissioned to inform specific components of policy (such as efficacy), the same process is rarely applied to the full decision-making process. Mathematical models provide a mechanism through which empirical evidence can be methodically and transparently integrated to address such questions. However, such models are often considered difficult to interpret. In addition, models provide estimates that need to be iteratively reevaluated as new data or considerations arise. Using the case study of a novel diagnostic for tuberculosis, a framework for improved collaboration between public health decision-makers and mathematical modellers that could lead to more transparent and evidence-driven policy decisions for infectious diseases in the future is proposed. The framework proposes that policymakers should establish long-term collaborations with modellers to address key questions, and that modellers should strive to provide clear explanations of the uncertainty of model structure and outputs. Doing so will improve the applicability of models and clarify their limitations when used to inform real-world public health policy decisions.

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“…By contrast, in South Africa, where Xpert testing has largely replaced smear microscopy as the first-line test, the national algorithm currently recommends mycobacterial culture for all HIV-infected TB suspects with a negative Xpert test. This is a costly strategy and there is some evidence that a second Xpert test may be more cost-effective in these patients [20]. Further research is urgently needed to identify the most cost-effective testing strategy, which will likely vary depending on prevalence of TB and rates of HIV infection and MDR-TB.…”

Section: What Are the Implications Of These Performance Data For Clinmentioning

confidence: 99%

Using Xpert MTB/RIF

Nicol¹,

Whitelaw²,

Stevens

2013

CRMR

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Xpert MTB/RIF is an automated real-time polymerase chain reaction test for simultaneous detection of tuberculosis and rifampicin resistance. Xpert MTB/RIF has demonstrated excellent accuracy in clinical evaluation studies, but has reduced sensitivity for detection of smear-negative tuberculosis. Since sample processing and detection are largely automated, Xpert MTB/RIF is potentially suitable for implementation in resource-limited settings. There are, however, a number of practical constraints to the use of Xpert at the point-of-care. Xpert remains a relatively costly test, and clear demonstration of cost-effectiveness will be needed to support efforts to scale up testing in high burden countries.

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Diagnosing Xpert MTB/RIF negative TB: Impact and cost of alternative algorithms for South Africa

Cited by 28 publications

References 13 publications

The Diagnostic Performance of a Single GeneXpert MTB/RIF Assay in an Intensified Tuberculosis Case Finding Survey among HIV-Infected Prisoners in Malaysia

The Diagnostic Performance of a Single GeneXpert MTB/RIF Assay in an Intensified Tuberculosis Case Finding Survey among HIV-Infected Prisoners in Malaysia

Bridging the gap between evidence and policy for infectious diseases: How models can aid public health decision-making

Using Xpert MTB/RIF

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