The study was conducted in the KwaZulu-Natal province in South Africa. The province has the second-highest population in the country with more than 11 million people. There are 11 districts in the province and one MDR-TB treatment facility per district.
In health facilities in the KwaZulu-Natal province, the initial diagnosis of tuberculosis and rifampicin resistance is routinely done using the Xpert (Xpert MTB/RIF, Cepheid, Sunnyvale, California, United States) in all patients suspected of tuberculosis disease. The Xpert was previously used but was later replaced by its successor, the Xpert MTB/RIF Ultra (Xpert Ultra, Cepheid, Sunnyvale, California, United States), in 2017. For patients with rifampicin-susceptible tuberculosis, no further DST is performed, and they are treated using first-line tuberculosis therapy. In patients with rifampicin-resistant tuberculosis on the Xpert (Ultra), a second sample is taken for culture and DST. Other indications for tuberculosis culture include treatment failure and paucibacillary tuberculosis that shows a negative result on the Xpert (Ultra).
During the study period between January 2014 and December 2014, the automated BACTEC Mycobacteria Growth Indicator Tube 960 system (Becton Dickinson, Sparks, Maryland, United States) was used for M. tuberculosis culture, and initial DST was done on all positive cultures using the MTBDRplus version 2 assay (Hain Lifescience, Nehren, Germany) to confirm rifampicin resistance and test for isoniazid resistance. The MTBDRplus assay uses DNA strip technology where the strip contains both wild-type probes and mutation probes for the commonly occurring mutations (S450L, H455Y, H455D, and D435V for rifampicin). The labelled polymerase chain reaction products from an amplified target are hybridised with specific probes immobilised on a strip (reverse hybridisation). Resistance is reported when there is a lack of binding to the wild-type probe with or without binding to a mutation probe.14 Isolates that were resistant to either rifampicin or isoniazid on the MTBDRplus assay were further tested for resistance to critical concentrations of isoniazid (0.2 µg/mL), rifampicin (1 µg/mL), ofloxacin (2 µg/mL), streptomycin (2 µg/mL), and kanamycin (5 µg/mL) using the 1% agar proportion method on Middlebrook 7H10 agar (Becton Dickinson, Sparks, Maryland, United States).15 The simultaneous performance of molecular and phenotypic rifampicin DST allowed the detection of discordance between these two tests.
In health facilities in the KwaZulu-Natal province, the initial diagnosis of tuberculosis and rifampicin resistance is routinely done using the Xpert (Xpert MTB/RIF, Cepheid, Sunnyvale, California, United States) in all patients suspected of tuberculosis disease. The Xpert was previously used but was later replaced by its successor, the Xpert MTB/RIF Ultra (Xpert Ultra, Cepheid, Sunnyvale, California, United States), in 2017. For patients with rifampicin-susceptible tuberculosis, no further DST is performed, and they are treated using first-line tuberculosis therapy. In patients with rifampicin-resistant tuberculosis on the Xpert (Ultra), a second sample is taken for culture and DST. Other indications for tuberculosis culture include treatment failure and paucibacillary tuberculosis that shows a negative result on the Xpert (Ultra).
During the study period between January 2014 and December 2014, the automated BACTEC Mycobacteria Growth Indicator Tube 960 system (Becton Dickinson, Sparks, Maryland, United States) was used for M. tuberculosis culture, and initial DST was done on all positive cultures using the MTBDRplus version 2 assay (Hain Lifescience, Nehren, Germany) to confirm rifampicin resistance and test for isoniazid resistance. The MTBDRplus assay uses DNA strip technology where the strip contains both wild-type probes and mutation probes for the commonly occurring mutations (S450L, H455Y, H455D, and D435V for rifampicin). The labelled polymerase chain reaction products from an amplified target are hybridised with specific probes immobilised on a strip (reverse hybridisation). Resistance is reported when there is a lack of binding to the wild-type probe with or without binding to a mutation probe.14 Isolates that were resistant to either rifampicin or isoniazid on the MTBDRplus assay were further tested for resistance to critical concentrations of isoniazid (0.2 µg/mL), rifampicin (1 µg/mL), ofloxacin (2 µg/mL), streptomycin (2 µg/mL), and kanamycin (5 µg/mL) using the 1% agar proportion method on Middlebrook 7H10 agar (Becton Dickinson, Sparks, Maryland, United States).15 The simultaneous performance of molecular and phenotypic rifampicin DST allowed the detection of discordance between these two tests.
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