Validation of microscopic observation drug susceptibility testing for rapid, direct rifampicin and isoniazid drug susceptibility testing in patients receiving tuberculosis treatment

J Coronel,M.H Roper,C Herrera,C Bonilla,O Jave,C Gianella,I Sabogal,V Huancaré,E Leo,A Tyas,A Mendoza-Ticona,L Caviedes,D.A.J Moore

doi:10.1111/1469-0691.12401

Abstract

Drug susceptibility testing (DST) is often needed in patients clinically failing tuberculosis (TB) therapy. Most studies of phenotypic direct drug susceptibility tests, such as microscopic observation drug susceptibility (MODS) tests, have been performed in patients not receiving TB treatment. The effect of ongoing TB treatment on the performance of MODS direct DST has not been previously explored, but patients failing such therapy constitute an important target group. The aim of this study was to determine the performance of MODS direct rifampicin and isoniazid DST in patients clinically failing first-line TB treatment, and to compare MODS direct DST with indirect proportion method DST. Sputa from 264 TB patients were cultured in parallel in Lowenstein–Jensen (LJ) and MODS assays; strains were tested for rifampicin and isoniazid susceptibility by the proportion method at the national reference laboratory. Ninety-three samples were culture-positive by LJ and MODS (concordance of 96%; kappa 0.92). With conventional MODS plate DST reading (performed on the same day as the sample is classified as culture-positive), the isoniazid DST concordance was 96.8% (kappa 0.89), and the concordance for rifampicin susceptibility testing was 92.6% (kappa 0.80). Reading of MODS DST plates 1 week after cultures had been determined to be culture-positive improved overall performance marginally—the isoniazid DST concordance was 95.7% (kappa 0.85); and the rifampicin DST concordance was 96.8% (kappa 0.91). Sensitivity for detection of multidrug-resistant TB was 95.8%. MODS testing provided reliable rifampicin and isoniazid DST results for samples obtained from patients receiving TB therapy. A modified DST reading schedule for such samples, with a final reading 1 week after a MODS culture turns positive, marginally improves the concordance with reference DST.

Highlights

Direct drug susceptibility testing (DST) is a potentially powerful tool in the global battle against drug-resistant tuberculosis (TB)
Overwhelming data obtained with several different methodologies have demonstrated that, whereas this concern might be warranted for ethambutol and streptomycin, direct DST shows high concordance with conventional indirect reference methods for both rifampicin and isoniazid [1,5,6,7]
Patients failing to respond to first-line TB therapy (2RHZE6 4HR2), defined as persistent symptoms and/or sputum smear non-conversion after 2 months of directly observed treatment, are routinely referred to respiratory physicians for evaluation, which usually includes conventional solid medium culture of a sputum sample followed by indirect DST by the proportion method on agar at the national TB reference laboratory

Summary

Introduction

Direct drug susceptibility testing (DST) is a potentially powerful tool in the global battle against drug-resistant tuberculosis (TB). By circumventing the delay inherent in primary culture and strain isolation, and the additional workload and further delay associated with the establishment of secondary cultures for indirect DST, clinicians and their patients have access to this important information in a clinically useful time frame [1,2,3,4]. Reservations about the validity of direct phenotypic DST for Mycobacterium tuberculosis are based upon a perceived need to control inoculum size. Overwhelming data obtained with several different methodologies have demonstrated that, whereas this concern might be warranted for ethambutol and streptomycin (which tend to not perform very well in direct DST), direct DST shows high concordance with conventional indirect reference methods for both rifampicin and isoniazid [1,5,6,7].

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