Abstract
BackgroundRapid diagnosis of drug-resistant Mycobacterium tuberculosis is a challenge in low-income countries. Phenotypic drug susceptibility testing using Sensititre® MycoTB assay and the resazurin microtitre plate assay (REMA) are relatively new innovative methods to determine drug susceptibility.ObjectivesThis study aimed to determine the performance of the Sensititre and REMA for M. tuberculosis drug susceptibility testing in a high-volume tuberculosis reference laboratory.MethodsA laboratory-based study was performed at the Inkosi Albert Luthuli Central Hospital Tuberculosis Laboratory from January 2014 to June 2015. The Sensititre® MycoTB plate and REMA were compared to the gold standard agar proportion method (APM) using 134 stored isolates.ResultsAgreement between the Sensititre® MycoTB plate and APM was observed with 98% sensitivity, 82% specificity, 94% positive and 93% negative predictive values of the Sensititre® MycoTB assay for the detection of rifampicin resistance and 97%, 96%, 99% and 88% for isoniazid resistance. Good categorical agreement between the REMA and the APM was observed among isolates with 89% sensitivity, 68% specificity, 89% positive and 68% negative predictive value for the detection of rifampicin resistance and 95%, 96%, 99% and 81% for isoniazid resistance. Results for the second-line drugs showed elevated minimum inhibitory concentrations for multidrug-resistant and extensively drug-resistant tuberculosis isolates.ConclusionThe REMA and Sensititre® MycoTB plate are attractive alternatives to the gold standard APM for the phenotypic detection of M. tuberculosis drug resistance.
Highlights
Multidrug-resistant tuberculosis has been declared a public health crisis by the World Health Organization (WHO).[1]
The time to results for the Sensititre® MycoTB method was as early as 7 days, with more reliable results being produced within 10 days
As phenotypic drug susceptibility testing (DST) is required for the determination of moxifloxacin susceptibility (WHO recommendation due to poor concordance of Genotype MTBDRsl with agar proportion method (APM)), this might prove problematic if the Sensititre® MycoTB assay is used.[1]
Summary
Multidrug-resistant tuberculosis has been declared a public health crisis by the World Health Organization (WHO).[1] The global burden of tuberculosis remains enormous with an incidence of 10 million new cases and a mortality of 1.3 million attributed to the disease worldwide in 2017.1 The 2018 WHO Global Tuberculosis Report documented new tuberculosis cases, which included an additional 300 000 tuberculosis cases among HIV-positive tuberculosis patients.[1]. South Africa is among the top 20 high-tuberculosis-burden countries worldwide and was previously ranked third following India and China.[1,2] Multidrug-resistant (MDR) tuberculosis is steadily increasing in South Africa; cases doubled from 7350 in 2007 to 14 000 in 2017.1,3 A form of tuberculosis known as extensively drug-resistant (XDR) tuberculosis has been reported in 92 countries. Treatments regimens for MDR tuberculosis (resistance to isoniazid and rifampicin) and XDR tuberculosis (resistance to any of the injectable drugs including fluoroquinolone, plus MDR tuberculosis),[5,6] http://www.ajlmonline.org. Phenotypic drug susceptibility testing using Sensititre® MycoTB assay and the resazurin microtitre plate assay (REMA) are relatively new innovative methods to determine drug susceptibility
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