ABSTRACT
Nucleic acid amplification tests offer shorter turnaround times for diagnosis of tuberculosis (TB) and drug resistance of isolates compared to conventional culture methods. The rapid molecular-based multidrug-resistant (MDR)-TB assay; GenoTyper MTBDRplus (Hain Lifescience) was evaluated in Gauteng; South Africa; as a pilot investigation to assess its performance for detection of MDR-TB in patients who were at high risk of drug-resistant TB. A total of 945 sputum specimens sequentially received within a period of six weeks from seven hospitals were assessed by MTBDRplus and compared to liquid culture drug susceptibility tests (DST) using the MGIT 960 system (BD Diagnostic Systems) as the `gold standard'. Of the 945 specimens processed; 731 had interpretable results from both tests and therefore were included in the analysis. The overall sensitivities of the MTBDRplus in detecting individual resistance to rifampicin (RMP) and isoniazid (INH); as well as MDR were 95.0; 93.4and 100; respectively. The specificities were 99.7for RMP; and 100for INH and MDR. The Genotyper MTBDRplus assay showed excellent concordance with the conventional `gold standard' MGIT DST; and it detected all the MDR-TB cases analysed
Subject(s)
Early Diagnosis , Polymerase Chain Reaction , Sputum , TuberculosisABSTRACT
SETTING: The epidemiology of extensively drug-resistant tuberculosis (XDR-TB), an emerging threat to TB control, is not well understood. OBJECTIVE: To gain insight into the genotypic population structure of XDR Mycobacterium tuberculosis strains in South Africa using a molecular approach and thereby determine whether XDR-TB is mainly acquired or transmitted. DESIGN: Sputum isolates from patients with multidrug-resistant tuberculosis (MDR-TB) were submitted to the National Referral Laboratory for second-line drug susceptibility testing. The XDR-TB isolates were spoligotyped and these data were compared to the geographic origin of the isolate. RESULTS: Of the 699 MDR-TB isolates submitted for testing between June 2005 and December 2006, 101 (17%) patients had a culture that was resistant to either ofloxacin or kanamycin, and 41 (6%) were resistant to both drugs (XDR-TB). Spoligotyping of the XDR-TB isolates identified 17 genotypes. As a result of the high genotypic diversity and geographical distribution, we estimate that between 63% and 75% of cases developed XDR-TB through acquisition. CONCLUSION: Acquisition of extensive drug resistance appears to be the primary mechanism driving the XDR-TB epidemic in South Africa. This urgent TB control issue has to be addressed to prevent the spread of this potentially incurable disease.