Spread of an emerging Mycobacterium tuberculosis drug-resistant strain in the western Cape of South Africa.

BACKGROUND

South Africa has a high burden of drug-resistant tuberculosis (TB).

METHODS

Routine drug susceptibility testing was performed prospectively over a 2-year period on Mycobacterium tuberculosis isolates in two health districts of the Western Province, South Africa. A cluster of drug-resistant strains that shared a rare mutation in katG315 was found in 64 of the 450 cases identified as having been infected with drug-resistant TB. Isolates belonging to this cluster were phenotypically and genotypically characterised. Epidemiological and clinical characteristics were used to identify mechanisms leading to the acquisition and spread of this drug-resistant strain.

RESULTS

An outbreak of an emerging non-Beijing drug-resistant strain infecting 64 pulmonary tuberculosis (PTB) cases was identified. This previously undetected genotype (now designated DRF150) is characterised by five IS6110 insertions, specific spoligotypes and high levels of resistance to the first-line TB medications isoniazid, streptomycin and rifampicin. In 45% of the cases it is also resistant to ethambutol and pyrazinamide. Key factors leading to the development and spread of this drug-resistant genotype were inappropriate chemotherapy, poor adherence to treatment and prolonged periods of infectiousness due to delays in susceptibility testing.

CONCLUSIONS

Molecular markers allowed early identification of an emerging non-Beijing drug-resistant strain.