Tuberculosis drug resistance in the Western Cape.

OBJECTIVES: Drug resistance is a serious problem in the treatment of tuberculosis and a threat to successful tuberculosis control programmes. Local health workers have expressed concern that the increasing tuberculosis epidemic in the Western Cape is partly attributable to drug resistance. The aim of this study was to determine the prevalence of tuberculosis drug resistance (including multidrug resistance) and to investigate possible relationships between drug resistance and patient demographic characteristics. DESIGN, SETTING, SUBJECTS, OUTCOME MEASURES: During a defined period, all adult (> or = 15 years) patients with pulmonary tuberculosis (confirmed by culture) from all tuberculosis clinics in the Western Cape were included. Previous tuberculosis treatment history was obtained by interviews, utilising a standardised questionnaire. Acquired drug resistance was determined on cultures from patients with a prior history of tuberculosis treatment, while initial resistance was determined from tuberculosis cases with no history of previous treatment.
RESULTS: Data from 7,266 patients were analysed. After adjusting for missing information by way of a random sample validation study, 32% of patients were found to have a history of previous treatment, 63% indicated no previous treatment, and in 5% the treatment history was unknown. Rates for initial resistance were found to be low at 3,9% for isoniazid, 1,1% for rifampicin and 0,2% for ethambutol. Combined resistance to isoniazid and rifampicin (multidrug resistance) was found to be 1,1% in patients not treated before. Acquired resistance rates were higher at 10,8% for isoniazid, 4,2% for rifampicin, 0,3% for ethambutol and 4,0% for multidrug resistance. Logistic regression analysis of the data indicated that drug resistance was not influenced by population group, gender or age. Patients with a history of tuberculosis treatment were found to be at an increased risk of developing drug resistance (relative risk 2,6). Some regions in the Western Cape had higher proportions of previously treated patients with consequent higher acquired resistance rates.
CONCLUSIONS: Results from this study indicated that drug resistance is currently not a major problem in the Western Cape, rates comparing favourably with those reported from developed countries and being much lower than those for developing countries. Every effort should therefore be made to maintain the status quo and to prevent the emergence of further resistance. The priority for tuberculosis control in the Western Cape should remain to limit transmission of the disease by reducing the infectious pool through improved cure of (especially) smear-positive cases.