Evolving rifampicin and isoniazid mono-resistance in a high multidrug-resistant and extensively drug-resistant tuberculosis region: a retrospective data analysis

OBJECTIVES: South Africa ranks among the highest drug-resistant tuberculosis (DR-TB) burdened countries in the world. This study assessed the changes in resistance levels in culture confirmed Mycobacterium tuberculosis (MTB) in the highest burdened province of South Africa during a period where major changes in diagnostic algorithm were implemented. SETTING: This study was conducted at the central academic laboratory of the KwaZulu-Natal province of South Africa. PARTICIPANTS: We analysed data for all MTB cultures performed in the KwaZulu-Natal province between 2011 and 2014. The data were collected from the laboratory information system. RESULTS: Out of 88 559 drug susceptibility results analysed, 18 352 (20.7%) were resistant to rifampicin (RIF) and 19 190 (21.7%) showed resistance to isoniazid (INH). The proportion of rifampicin resistant cases that were mono-resistant increased from 15.3% in 2011 to 21.4% in 2014 while INH mono-resistance (IMR) showed a range between 13.8% and 21.1%. The multidrug-resistant tuberculosis (MDR-TB) rates increased from 18.8% to 23.9% and the proportion of MDR-TB cases that had extensively drug-resistant tuberculosis remained between 10.2% and 11.1%. Most drug resistance was found in females between the ages of 15 and 44 years and the northern districts bordering high MDR-TB regions had the highest MDR-TB rates. CONCLUSION: Our findings show increasing RIF mono-resistance (RMR) and a substantial amount of IMR. This highlights a need for an initial test that detects resistance to both these drugs so as to avoid using RIF monotherapy during continuous phase of treatment in patients with IMR. Furthermore, addition of INH will benefit patients with RMR. Although DR-TB is widespread, HIV and migration influence its distribution; therefore, TB control strategies should include interventions that target these aspects.