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.