Primary Drug Resistance Patterns of Mycobacterium Tuberculosis Isolates Among New Pulmonary Tuberculosis Patients in Bahir Dar, Ethiopia

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Addis Ababa University


The increase in drug resistant tuberculosis, and particularly multi-drug resistant tuberculosis (MDR-TB) as well as the neglect of discovery and development of new anti-TB drugs that are active against TB/ MDR-TB at present, increased the need for knowledge of the prevalence and patterns of primary resistance among Mycobacterium tuberculosis isolates in the community. A total of 76 M. tuberculosis isolates were recovered from sputa specimens of newly diagnosed pulmonary tuberculosis (PTB) patients in Bahir Dar, Ethiopia and confirmed by culture and standard biochemical tests on L-J media. The specimens were collected between February and April 2001. Drug susceptibility testing was performed according to the indirect proportion method. The prevalence and patterns of primary resistance were determined and any association between patients' characteristics (sex and age) and primary resistance were analyzed using chi-square test. The results of the present study showed that primary mono-resistance was highest to streptomycin (14.5 %) followed by isoniazid (2.6 %). All isolates were susceptible to rifampicin and ethambutol. Primary resistance to any drug was found in 14 of new PTB patients (18.4 %); and any primary resistance to streptomycin was 15.8 %; any isoniazid resistance was 3.9 %; any rifampicin resistance was 1.3 %, and it was nil to ethambutol. The rate of Primary MDR-TB was 1.3 %. Single drug resistance was higher in males (n=8, 61.5 % of mono-resistant cases) than in females (n=5, 38.5 %). Primary resistance to a single drug was found in 4 patients in the age group 15-24 (30.8 %), 4 in the group 25-34 (30.8 %) and 5 in the group 35-44 (38.5 %). Thus, the proportion of patients that had primary mono-resistance was similar in all age groups and the age groups between 15-44 were totally affected by primary drug resistant strains. Primary MDR-TB (with HRS pattern) occurred in one patient (1.3 %) belonged to the age group 25-34. Single drug resistance to streptomycin was found in 8 males (73 %) and in 3 female patients (27 %). Isoniazid monoresistance was found only in female patients (n = 2, 100 %). The age range of TB patients that had primary resistant isolates of M. tuberculosis were between 15-44 years, with mean age of 27.4 years. However, primary resistance was not associated with age and gender (P>0.05). The drugs isoniazid, ethambutol and rifampicin remain drugs of choice to treat the majority of drug susceptible TB cases in Bahir Dar. The results of this study underscore the need for periodic monitoring of drug resistance and improving in TB control performance both at local and country level.