Anti-tuberculosis drug resistance among retreatment patients seen at St Peter Tuberculosis Specialized Hospital.

BACKGROUND: Resistance to first line anti-tuberculosis (TB) drugs is an increasing concern. Drug sensitivity of mycobacterial isolates from patients who failed treatment may indicate the potential sources of spread and the emerging patterns of resistance. OBJECTIVE: To determine the prevalence of resistance to the main anti TB drugs among re-treatment cases who had previously received loose drugs or the 3FDC regimen in the intensive phase. METHODS: Mycobacteria were isolated on Lowenstein-Jensen media from sputum of smear positive pulmonary TB patients who visited the St Peter's TB Specialized Hospital, a referral TB Hospital in Addis Ababa, for retreatment between December 2001 and October 2002. The susceptibility of isolates to rifampicin, isoniazid ethambutol and streptomycin was tested using the standard modified proportion method RESULT: Of the 84 Mycobacterium tuberculosis isolates, resistance to at least one drug was observed in 53.6% and 26.2% of the isolates were multi drug resistant (MDR). MDR was more frequent among patients who had previously been treated with the 3FDC regimen than among patients previously treated with loose drugs (p < 0.05). The proportion of strains resistant to rifampicin and ethambutol was significantly higher than in an earlier report from Addis Ababa. CONCLUSION: MDR is an emerging problem among re-treatment cases of pulmonary TB in Addis Ababa. The problem of drug resistance should be addressed by operational research on drug regimens, effectiveness and delivery.

Direct colorimetric assay for rapid detection of rifampin-resistant Mycobacterium tuberculosis.

The colorimetric 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay was standardized for direct detection of rifampin-resistant Mycobacterium tuberculosis in sputum samples. The sensitivity and specificity of the direct MTT assay matched those of the standard indirect susceptibility assay on 7H10 medium, and interpretable results were obtained for 98.5% of the samples within 2 weeks. Traditional methods of in vitro drug susceptibility testing are time consuming and laborious. Susceptibility tests on clinical isolates require 6 to 9 weeks, and tests conducted directly on smear-positive samples take about 3 weeks (International Union Against Tuberculosis and Lung Disease, The public health service national tuberculosis reference laboratory and the national laboratory network. Minimum requirements, role and operation in a low-income country, Paris, France, 1998, and P. T. Kent and G. P. Kubica, Public health mycobacteriology. A guide for the level III laboratory, Centers for Disease Control and Prevention, Atlanta, Ga., 1985). More-rapid methods are available but are very expensive for routine use under program conditions in countries with high levels of tuberculosis endemicity.