Background The emergence and transmission of multidrug-resistant (MDR) and extensively drug-resistant (XDR) Mycobacterium tuberculosis (Mtb) strains is a serious threat to tuberculosis control in Botswana. Early detection of drug-resistant isolates is critical to ensure optimal treatment and thereby improve treatment outcomes. The objective of this study was to determine the extent of second-line drug resistance among drug-resistant Mtb-isolates from Botswana.
Methods A total of 60 drug-resistant Mtb isolates received at Botswana National Tuberculosis Reference Laboratory between 2012 and 2013 were analysed. DNA was extracted from BD Mycobacterial Growth Indicator Tubes (MGIT) using GenoLyse DNA isolation kit (Hain Lifescience). Spoligotyping was done using a commercially available spoligotyping kit (Isogen Life Science). The spoligotype patterns were compared with existing patterns in the SITVIT2 Web database. GenoType MTBDRs assay (Hain Lifescience) was used for second-line drug susceptibility testing. Fisher’s exact test was used to test for association between drug resistance patterns and HIV status, lineage and geographical location.
Results Seventeen distinct spoligotype patterns were detected amongst the 60 drug-resistant isolates. The most predominant lineages were Euro-American (58.3%), East Asian (25%) and Indo-Oceanic (15%). Fifty (83.3%) were MDR, 7 (11.7%) were resistant to fluoroquinolones (Pre-XDR) whereas 3 (5%) were resistant to both fluoroquinolones and second-line injectable drugs (XDR). Drug resistance profiles were significantly associated with Mtb lineage (p<0.001). There was no association between drug resistance profile and HIV status (p=0.057) and geographical location (p=0.372).
Conclusion This study highlights the importance of including second-line drug susceptibility testing in a testing algorithm in Botswana. The detection of XDR isolates among MDR-TB isolates highlights the ongoing evolution of resistance and the need for strengthened treatment regimens to improve treatment outcomes and to prevent the spread of these highly resistant strains. Second-line testing will be essential if the 9 month MDR regimen is used in Botswana.
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