RESUMO
OBJECTIVE: To determine the drug sensitivity of Mycobacterium tuberculosis strains isolated from pretreatment (primary) cases of pulmonary tuberculosis. DESIGN: A descriptive study. SETTING: The Central Chest Clinic, Colombo. PATIENTS: 103 patients with pulmonary tuberculosis who have not taken anti-tuberculosis drugs previously. MEASUREMENTS: Antibiotic sensitivity pattern of M tuberculosis isolates for isoniazid (INAH), ethambutol (EMB), rifampicin (RMP) and streptomycin (SM) tested in drug incorporated Lowenstein Jenson (LJ) medium using resistance ratio method. RESULTS: 15.5% isolates of M tuberculosis were resistant to at least one drug. Resistance to a single drug was found to be most prevalent (69%) among the resistant isolates and among these INAH resistance was most prevalent followed by streptomycin. None of the isolates were resistant to all four drugs. Resistance rates to individual drugs were INAH 9.7%. SM 6.7% EMB 2.9% and RMP 2.9%. CONCLUSIONS: Since the introduction of RMP and EMB in the treatment regimens from mid-1970s the incidence of tuberculosis and rate of primary drug resistance to anti-tuberculosis drugs has not changed significantly (p > 0.05) when compared with the results of studies conducted previously (2, 3). However, it is recommended that regular surveillance of drug sensitivity pattern should be maintained to determine alternate drug regimes and to detect the spread of resistant strains in the community.