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Evaluation of the cobas® MTB Real-Time PCR plus MTB-RIF/INH assay in a low incidence country

J Koglin(1) J Köffer(1) U Betz(1) U Eigner(1) E Richter(1)

1:MVZ Labor Limbach Heidelberg

The cobas® MTB Real-Time PCR assay is intended for the rapid detection of MTBC in clinical specimens with a reflex-test, the cobas® MTB-RIF/INH assay, to detect resistance to isoniazid (INH) and rifampicin (RMP) in MTBC positive specimens. WHO recommended this as one of the moderate complexity assays to rapidly detect MTBC and additional drug resistance. We evaluated this assay for its applicability in a low incidence country with low resistance rates. For this purpose, 500 sputum specimens were analysed in parallel by culture and by the cobas® assay. MTBC positive specimens were subsequently analysed for INH and RMP resistance. To evaluate the ability of the cobas® MTB-RIF/INH assay to detect different mutations causing resistance to INH and RMP a collection of 34 TB strains with different well-described mutations in the rpoB, inhA or katG genes was deployed. In total, the cobas® MTB Real-Time PCR assay presented a high sensitivity (91.8%), even in smear negative specimens (85.1%), and the detection of all smear positive cases (100%). All analysable positive samples were correctly identified as susceptible to INH and RMP. Using the strain collection with selected mutations, 41 of 45 cases of drug resistance were detected with the cobas® MTB-RIF/INH assay. Resistances not recognized by the assay were caused by very rare mutations, according to the WHO catalogue of mutations. Overall, the cobas® MTB Real-Time PCR plus MTB-RIF/INH assay enables a largely automated testing for the detection of TB and drug resistance with the possibility of a high throughput capacity.

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