Molecular characterization and drug susceptibility of isolates from MDR-TB patients in the Eastern Cape and North West provinces of South Africa

[摘要] ENGLISH SUMMARY: South Africa is among the countries facing rising numbers of Mycobacterium tuberculosis (Mtb) drug resistant strains. In 2000, DOTS-Plus strategy was introduced nationally to combat drug resistant tuberculosis (TB). This necessitated the introduction of drug susceptibility testing for second-line drugs (SLDs) in order to detect and treat cases in a timely and effective manner. However, this was only routinely implemented following the description of extensively drug resistant (XDR-TB, defined as MDR-TB plus resistance to a fluoroquinolone and a second-line injectable, in South Africa in 2006.The impact of implementing a standardized MDR-TB therapy policy in South Africa on individual treatment outcomes and acquisition of additional drug resistance has not been widely documented. Improved knowledge of factors that lead to acquisition of second-line drug resistance will help better predict who is most at risk of drug resistance and contribute to the development of new tools and strategies to combat MDR-TB. To fill this gap, we sought to determine the prevalence of SLD resistance among MDR-TB patients in the DOTS-Plus cohort and its impact on treatment outcomes for these patients in two provinces in South Africa; Eastern Cape (EC) and North West (NW) province.The results show that treatment success was strongly influenced by the setting where the patients were treated. Default and death accounted for 58.1% (193/333) of all unfavourable outcomes in provinces. The EC province had the lowest (13.4%, 51/381) cure rate and the highest default rate of 38.3%; compared to a default rate of 6.39% in NW.This study also describes the resistance patterns against second line drugs among newly diagnosed MDR-TB patients in the NW and EC province using Genotype MTBDRsl assay (version 1) and targeted sequencing of genes known to confer resistance, and how these patients acquired resistance during treatment. These finding have important implications for infection control, because undiagnosed highly resistant strains could have been transmitted to contacts during treatment. The concordance between Genotype MTBDRsl and sequencing was 82% for all gyrA gene and 67% for the rrs gene. Resistance to all drugs (including ethambutol) tested at baseline was 15.8% (47/298) and resistance to both ofloxacin and kanamycin was 1.3% (4/298). Heteroresistance associated with the gyrA and embB gene was also observed. Furthermore, the study discusses the implementation of the DOTS-Plus policy with regards to whether it significantly contributed to the emergence of XDR-TB in individual patients. Implications for implementation of standardized MDR-TB treatment in the absence of knowledge of baseline resistance are also discussed.Analysis of 48 MDR-TB patients, with initial and last available isolates, showed that 45,8% gained resistance to second line drugs during treatment which suggests that the combination of in-hospital treatment with a standardized MDR-TB treatment regimen increased the risk to the patient gaining XDR during treatment.This thesis has contributed to our understanding of drug resistance in TB, and implications of implementing standardized MDR-TB treatment in South Africa. We propose an algorithm for rapidly diagnosing patients that are at risk of extensively drug resistant tuberculosis (XDR-TB) using a combination of the methods endorsed by the World Health Organization (WHO).

[发布机构] Stellenbosch University