Abstract
BackgroundDrug-resistant tuberculosis (DR-TB) is considered a real threat to the achievement of TB control. Testing of mycobacterial culture and testing of drug susceptibility (DST) capacity are limited in resource-poor countries, therefore inadequate treatment may occur, favouring resistance development. We evaluated the molecular assay GenoType® MTBDRplus (Hain Lifescience, Germany) in order to detect DR-TB directly in clinical specimens as a means of providing a more accurate management of chronic TB patients in Burkina Faso, a country with a high TB-HIV co-infection prevalence.MethodsSamples were collected in Burkina Faso where culture and DST are not currently available, and where chronic cases are therefore classified and treated based on clinical evaluation and sputum-smear microscopy results. One hundred and eight chronic TB patients (sputum smear-positive, after completing a re-treatment regimen for pulmonary TB under directly observed therapy) were enrolled in the study from December 2006 to October 2008. Two early morning sputum samples were collected from each patient, immediately frozen, and shipped to Italy in dry ice. Samples were decontaminated, processed for smear microscopy and DNA extraction. Culture was attempted on MGIT960 (Becton Dickinson, Cockeysville, USA) and decontaminated specimens were analyzed for the presence of mutations conferring resistance to rifampin and isoniazid by the molecular assay GenoType® MTBDRplus.ResultsWe obtained a valid molecular test result in 60/61 smear-positive and 47/47 smear-negative patients.Among 108 chronic TB cases we identified patients who (i) harboured rifampin- and isoniazid-susceptible strains (n 24), (ii) were negative for MTB complex DNA (n 24), and (iii) had non-tuberculous mycobacteria infections (n 13). The most represented mutation conferring rifampin-resistance was the D516V substitution in the hotspot region of the rpoB gene (43.8% of cases). Other mutations recognized were the H526D (15.6%), the H526Y (15.6%), and the S531L (9.4%).All isoniazid-resistant cases (n 36) identified by the molecular assay were carrying a S315T substitution in the katG gene. In 41.7% of cases, a mutation affecting the promoter region of the inhA gene was also detected.ConclusionThe GenoType® MTBDRplus assay performed directly on sputum specimens improves the management of chronic TB cases allowing more appropriate anti-TB regimens.
Highlights
Drug-resistant tuberculosis (DR-TB) is considered a real threat to the achievement of TB control
The GenoType® MTBDRplus assay performed directly on sputum specimens improves the management of chronic TB cases allowing more appropriate anti-TB regimens
The GenoType® MTBDRplus test was performed on all samples regardless of the sputum smear results
Summary
Drug-resistant tuberculosis (DR-TB) is considered a real threat to the achievement of TB control. Standardized and optimised MTB culture and DST procedures require equipped, safe laboratories and trained human resources operating under quality assurance protocols. For all of these reasons, mycobacterial culture and DST capabilities are severely limited in resource-poor countries. In response to the growing problem of MDR-TB and the threat of an epidemic of XDR-TB, the STOP TB strategy has been revised to include universal access to diagnosis and treatment for all patients with MDR-TB by 2015 [10,11] This plan calls for accelerated access to rapid testing for rifampin (RIF) resistance in order to improve case detection in all patients with suspected MDR- and XDR-TB. Detection of MDR-TB and XDR-TB is critical to initiating appropriate treatment, reducing morbidity and mortality, and preventing further transmission of drugresistant MTB strains
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