Low Levels of Extensively Drug-resistant Tuberculosis among Multidrug Resistant Tuberculosis Isolates and Their Relationship to Risk Factors: Surveillance in Tehran, Iran; 2006 to 2014

OBJECTIVES: Extensively drug-resistant tuberculosis (XDR-TB) is more expensive and difficult to treat than multidrug-resistant tuberculosis (MDR-TB), and outcomes for patients are much worse; therefore, it is important that clinicians understand the magnitude and distribution of XDR-TB. We conducted a retrospective study to compare the estimated incidence of and risk factors for M/XDR-TB with those of susceptible TB controls. METHODS: Sputum culture and drug susceptibility testing (DST) were performed in patients with known or suspected TB. Strains that were identified as MDR were subjected to DST for second-line drugs using the proportion method. RESULTS: Among 1,442 TB patients (mean age, 46.48 ± 21.24 years) who were culture-positive for Mycobacterium tuberculosis, 1,126 (78.1%) yielded isolates that were resistant to at least one first-line drug; there were 33 isolates (2.3%) of MDR-TB, of which three (0.2%) were classified as XDR-TB. Ofloxacin resistance was found in 10 (0.7%) isolates. Women were 15% more likely than men to yield M/XDR-TB isolates, but this difference was not significant. In a multivariate analysis comparing susceptible TB with X/MDR-TB, only one variable—the number of previous treatment regimens—was associated with MDR (odds ratio, 1.06; 95% confidence interval, 1.14–21.2). CONCLUSION: The burden of M/XDR-TB cases is not sizeable in Iran. Nonetheless, strategies must be implemented to identify and cure patients with pre-XDR-TB before they develop XDR-TB. Our results provide a greater understanding of the evolution and spread of M/XDR-TB in an environment where drug-resistant TB has a low incidence.