The diagnostic accuracy of the GenoType® Mtbdr sl assay for the detection of resistance to second-line anti-tuberculosis drugs

Abstract

Background

Accurate and rapid tests for tuberculosis (TB) drug resistance are critical for improving patient care and decreasing the transmission of drug-resistant TB. Genotype®MTBDR sl (MTBDR sl) is the only commercially-available molecular test for detecting resistance in TB to the fluoroquinolones (FQs; ofloxacin, moxifloxacin and levofloxacin) and the second-line injectable drugs (SLIDs; amikacin, kanamycin and capreomycin), which are used to treat patients with multidrug-resistant (MDR-)TB.

Objectives

To obtain summary estimates of the diagnostic accuracy ofMTBDR sl for FQ resistance, SLID resistance and extensively drug-resistant TB (XDR-TB; defined asMDR-TB plus resistance to a FQand a SLID) when performed (1) indirectly (ie on culture isolates confirmed as TB positive) and (2) directly (ie on smear-positive sputum specimens).

To compare summary estimates of the diagnostic accuracy of MTBDR sl for FQ resistance, SLID resistance and XDR-TB by type of testing (indirect versus direct testing).

The populations of interest were adults with drug-susceptible TB or drug-resistant TB. The settings of interest were intermediate and central laboratories.

Search methods

We searched the following databases without any language restriction up to 30 January 2014: Cochrane Infectious Diseases Group Specialized Register; MEDLINE; EMBASE; ISI Web of Knowledge; MEDION; LILACS; BIOSIS; SCOPUS; the metaRegister of Controlled Trials; the search portal of the World Health Organization International Clinical Trials Registry Platform; and ProQuest Dissertations & Theses A&I.

Selection criteria

We included all studies that determined MTBDR sl accuracy against a defined reference standard (culture-based drug susceptibility testing (DST), genetic testing or both).We included cross-sectional and diagnostic case-control studies.We excluded unpublished data and conference proceedings.

Data collection and analysis

For each study, two review authors independently extracted data using a standardized form and assessed study quality using the Quality Assessment of Diagnostic Accuracy Studies (QUADAS-2) tool. We performed meta-analyses to estimate the pooled sensitivity and specificity of MTBDR sl for FQ resistance, SLID resistance, and XDR-TB. We explored the influence of different reference standards. We performed the majority of analyses using a bivariate random-effects model against culture-based DST as the reference standard.

Main results

We included 21 unique studies: 14 studies reported the accuracy of MTBDR sl when done directly, five studies when done indirectly and two studies that did both. Of the 21 studies, 15 studies (71%) were cross-sectional and 11 studies (58%) were located in lowincome or middle-income countries. All studies but two were written in English. Nine (43%) of the 21 included studies had a high risk of bias for patient selection. At least half of the studies had low risk of bias for the other QUADAS-2 domains.

As a test for FQ resistance measured against culture-based DST, the pooled sensitivity of MTBDR sl when performed indirectly was 83.1% (95% confidence interval (CI) 78.7% to 86.7%) and the pooled specificity was 97.7% (95% CI 94.3% to 99.1%), respectively (16 studies, 1766 participants; 610 confirmed cases of FQ-resistant TB; moderate quality evidence).When performed directly, the pooled sensitivity was 85.1% (95% CI 71.9% to 92.7%) and the pooled specificity was 98.2% (95% CI 96.8% to 99.0%), respectively (seven studies, 1033 participants; 230 confirmed cases of FQ-resistant TB; moderate quality evidence). For indirect testing for FQ resistance, four (0.2%) of 1766MTBDR sl results were indeterminate, whereas for direct testing 20 (1.9%) of 1033 wereMTBDR sl indeterminate (P < 0.001).

As a test for SLID resistance measured against culture-based DST, the pooled sensitivity of MTBDR sl when performed indirectly was 76.9% (95% CI 61.1% to 87.6%) and the pooled specificity was 99.5% (95% CI 97.1% to 99.9%), respectively (14 studies, 1637 participants; 414 confirmed cases of SLID-resistant TB; moderate quality evidence). For amikacin resistance, the pooled sensitivity and specificity were 87.9% (95% CI 82.1% to 92.0%) and 99.5% (95% CI 97.5% to 99.9%), respectively. For kanamycin resistance, the pooled sensitivity and specificity were 66.9% (95% CI 44.1% to 83.8%) and 98.6% (95% CI 96.1% to 99.5%), respectively. for capreomycin resistance, the pooled sensitivity and specificity were 79.5% (95% CI 58.3% to 91.4%) and 95.8% (95% CI 93.4% to 97.3%), respectively. When performed directly, the pooled sensitivity for SLID resistance was 94.4% (95% CI 25.2% to 99.9%) and the pooled specificity was 98.2% (95% CI 88.9% to 99.7%), respectively (six studies, 947 participants; 207 confirmed cases of SLIDresistant TB, 740 SLID susceptible cases of TB; very low quality evidence). For indirect testing for SLID resistance, three (0.4%) of 774 MTBDR sl results were indeterminate, whereas for direct testing 53 (6.1%) of 873 were MTBDR sl indeterminate (P < 0.001).

As a test for XDR-TB measured against culture-based DST, the pooled sensitivity of MTBDR sl when performed indirectly was 70.9% (95%CI 42.9%to 88.8%) and the pooled specificitywas 98.8%(95%CI 96.1%to 99.6%), respectively (eight studies, 880 participants; 173 confirmed cases of XDR-TB; low quality evidence).

Authors’ conclusions

In adults with TB, a positiveMTBDR sl result for FQ resistance, SLID resistance, or XDR-TB can be treated with confidence. However, MTBDR sl does not detect approximately one in five cases of FQ-resistant TB, and does not detect approximately one in four cases of SLID-resistant TB. Of the three SLIDs, MTBDR sl has the poorest sensitivity for kanamycin resistance. MTBDR sl will miss between one in four and one in three cases of XDR-TB. The diagnostic accuracy of MTBDR sl is similar when done using either culture isolates or smear-positive sputum. As the location of the resistance causing mutations can vary on a strain-by-strain basis, further research is required on test accuracy in different settings and, if genetic sequencing is used as a reference standard, it should examine all resistancedetermining regions. Given the confidence one can have in a positive result, and the ability of the test to provide results within a matter of days, MTBDR sl may be used as an initial test for second-line drug resistance. However, when the test reports a negative result, clinicians may still wish to carry out conventional testing.

Plain Language Summary

The rapid test GenoType® MTBDR sl for testing resistance to second-line TB drugs

Background

Different drugs are available to treat people with tuberculosis (TB), but resistance to these drugs is a growing problem. People with drug-resistant TB are more likely to die than people with drug-susceptible TB. People with drug-resistant TB require “second-line” TB drugs that, compared with “first-line” TB drugs used to treat drug-susceptible TB, cause more side effects and must be taken for longer. Extensively drug-resistant TB (XDR-TB) is a type of TB that is resistant to almost all TB drugs. A rapid and accurate test could identify people with drug-resistant TB, likely improve patient care, and reduce the spread of drug-resistant TB.

Test evaluated by this review

GenoType® MTBDR sl (MTBDR sl) is the only rapid test that detects resistance to second-line fluoroquinolone drugs and the secondline injectable drugs. The test also detects XDR-TB. MTBDR sl can be performed on TB bacteria grown by culture from sputum, which takes a long time (indirect testing), or immediately on sputum (direct testing).

Main results

We examined evidence available up to 30 January 2014 and included 21 studies, 11 of which were in low-income or middle-income countries.

What do these results mean?

Fluoroquinolone drugs

By indirect testing, the test detected 83% of people with fluoroquinolone resistance and rarely gave a positive result for people without resistance. In a population of 1000 people,where 170 have fluoroquinolone resistance,MTBDR sl will correctly identify 141 people with fluoroquinolone resistance and miss 29 people. In this same population of 1000 people, where 830 people do not have fluoroquinolone resistance, the test will correctly classify 811 people as not having fluoroquinolone resistance and misclassify 19 people as having resistance ( moderate quality evidence).

By direct testing, the test detected 85% of people with fluoroquinolone resistance and rarely gave a positive result for people without resistance ( moderate quality evidence).

Second-line injectable drugs

By indirect testing, the test detected 77%of people with second-line injectable drug resistance and rarely gave a positive result for people without resistance. In a population of 1000 people, where 230 have second-line injectable drug resistance, MTBDR sl will correctly identify 177 people with second-line injectable drug resistance and miss 53 people. In this same population of 1000 people, where 770 do not have second-line injectable drug resistance, the test will correctly classify 766 people as not having second-line injectable drug resistance and misclassify four people as having resistance ( moderate quality evidence).

By direct testing, the test detected 94% of people with second-line injectable drug resistance and rarely gave a positive result for people without resistance ( very low quality evidence).

XDR-TB

By indirect testing, the test detected 71% of people with XDR-TB and rarely gave a positive result for people without XDR-TB. In a population of 1000 people, where 80 have XDR-TB, MTBDR sl will correctly identify 57 people with XDR-TB and miss 23 people. In this same population of 1000 people, where 920 do not have XDR-TB, the test will correctly classify 909 people as not having XDRTB and misclassify 11 people as having XDR-TB ( low quality evidence).

There was insufficient evidence to determine the accuracy of MTBDR sl by direct testing for XDR-TB.

Conclusions

The results show that a positive MTBDR sl result for resistance to the fluoroquinolone drugs or the second-line injectable drugs is reliable evidence that the person has drug-resistant TB and further conventional drug-resistance testing is not required. However, when the test reports a negative result, clinicians may still wish to carry out conventional testing.