Characterizing Mycobacterium tuberculosis isolates from Karachi, Pakistan: drug resistance and genotypes

SummaryObjectivesTo study the prevalence, risk factors, and genotypes of drug-resistant Mycobacterium tuberculosis in Karachi.MethodsPulmonary tuberculosis (TB) patients were recruited in a cross-sectional study (2006–2009). Drug susceptibility testing was performed for culture-positive cases (n = 1004). Factors associated with drug resistance were evaluated using logistic regression analysis. Strains were typed using spoligotyping and mycobacterial interspersed repetitive units–variable number tandem repeat (MIRU–VNTR). The associations of genotype and drug resistance were explored using the Chi-square test.ResultsResistance rates – new and previously treated – were as follows: multidrug-resistant (MDR)-TB, 2.4% and 13.9%, respectively; rifampin (RIF) monoresistance, 0.1% and 0.6%, respectively; any isoniazid (INH) resistance, 8.9% and 28.5%, respectively; and INH monoresistance, 3.0% and 6.3%, respectively. Prior TB treatment was a risk factor for MDR-TB (adjusted odds ratio (AOR) 6.8, 95% confidence interval (CI) 3.5–13.1) and INH monoresistance (AOR 2.4, 95% CI 1.1–5.2). Additional risk factors included low socioeconomic status for INH monoresistance (AOR 3.3, 95% CI 1.7–6.5), and belonging to Balouchi (AOR 9.2, 95% CI 2.5–33.4), Sindhi (AOR 4.1, 95% CI 1.2–13.5), or Pakhtun (AOR 3.4, 95% CI 1.0–11.2) ethnicity for MDR-TB. Although Central Asian strain (55.6%) was the most prevalent genotype, MDR-TB was significantly associated with Haarlem (H) genogroup (crude OR 9.2, 95% CI 3.6–23.8).ConclusionsAn MDR-TB rate of 2.4% is reported in new patients. Low RIF monoresistance supports the use of RIF as a marker for MDR-TB in this population. The need to strengthen TB care in the identified at-risk groups is emphasized. Based on INH resistance rates, a review of national treatment/prevention regimens relying on INH is suggested.