Low Level of Extensively Drug-resistant Tuberculosis Among MDR-TB Isolates and its Relationship to Risk Factors: Surveillance in Tehran-Iran, 2006–2014

ObjectivesExtensively drug-resistant tuberculosis (XDR-TB) is more expensive and difficult to treat than multidrug-resistant TB (MDR-TB) and outcomes for patients are much worse, therefore understanding the magnitude and distribution of XDR-TB is important. A retrospective study was conducted to estimate the incidence of and risk factors for, multidrug XDR-TB (M/XDR-TB) as compared to susceptible controls.MethodsSputum culture and drug susceptibility testing (DST) were done for patients with known or suspected TB. The strains that were identified as MDR were subjected to DST for second line drugs (SLD) by using the proportion method.ResultsAmong 1,442 TB patient cases (mean age, 46.48 ± 21.24 years) culture-positive for Mycobacterium tuberculosis, 1,126 (78.1%) isolates were resistant to at least one first line drug; 33 cases (2.3%) were MDR-TB, of which, three isolates (0.2%) were classified as having XDR-TB. Ofloxacin resistance was found in 10 (0.7%) isolates. The odds of having M/XDR-TB were found to be 15% higher among females than males, but the difference was not significant. In the multivariate analysis, only one variable, number of previous treatment regimens, was associated with MDR as compared to susceptible TB [odds ratio (OR) 1.06, 95% confidence intervals (CI) 1.14–21.2].ConclusionThe burden of M/XDR-TB cases is not sizeable in Iran. However, we must implement strategies to identify and cure patients with pre-XDR-TB before they develop XDR-TB. Our results help provide an understanding of the evolution and spread of M/XDR-TB in a low-incidence setting of drug-resistant TB and its relationship with risk factors for the assessment of future treatment changes and interventions