Anti-tuberculosis drug resistance and associated risk factors in a tertiary level TB center in Iran: a retrospective analysis.

INTRODUCTION This study aimed to determine first-line anti-tuberculosis drug resistance rates in new and previously treated cases and to identify risk factors associated with multidrug resistant tuberculosis (MDR-TB) at the National Reference Tuberculosis Laboratory of Iran. METHODOLOGY This was a retrospective analysis of all confirmed TB patients from December 2000 to June 2005. Drug susceptibility testing to isoniazid, rifampicin, streptomycin, ethambutol and pyrazinamide was performed on Löwenstein-Jensen (LJ) medium according to the proportion method. RESULTS Mycobacterium tuberculosis strains were isolated from 1,742 patients with TB, of whom 935 (53.7%) were male. The mean age of patients was 44.2 ± 17.4 years (SD). A total of 1,074 patients were native Iranians while 668 (38.3%) were immigrant patients. Out of 1,139 (65.4%) new cases, 340 (29.9%) had at least one drug resistance. Of 603 (34.6%) previously treated cases, 416 (69.0%) had resistant strains. There were 263 patients (15.1%) with MDR-TB, 72 of whom were new (6.3% of all new cases) and 191 were previously treated (31.7% of all previously treated cases). Factors associated with MDR-TB included age under 45 years, male sex, previous TB treatment, immigration, poor living conditions, and unemployment. CONCLUSIONS The high rate of initial resistance in MDR-TB cases and the high rate of MDR-TB in a young age group were indicators of recent transmission. Therefore, closer monitoring of transmission trends of drug resistant strains should be considered as priority, to ensure a successful TB control programme.