Detection of katG and inhA mutations to guide isoniazid and ethionamide use for drug-resistant tuberculosis

BACKGROUND: Depending on the presence of mutations that determine isoniazid (INH) susceptibility (katG and inhA), Mycobacterium tuberculosis may be susceptible to high doses of INH or ethionamide (ETH). OBJECTIVE: To describe the INH resistance profile and association of katG mutation with previous INH treatment and level of drug resistance based on rapid molecular drug susceptibility testing (DST) in southern Brazil and central Mozambique. DESIGN: Descriptive study of 311 isolates from Ribeirao Preto, Sao Paulo, Brazil (2011-2014) and 155 isolates from Beira, Mozambique (2014-2015). Drug resistance patterns and specific gene mutations were determined using GenoType (R) MTBDRplus. RESULTS: katG gene mutations were detected in 12/22 (54.5%) Brazilian and 32/38 (84.2%) Mozambican SUMMARY isolates. inhA mutations were observed in 9/22 (40.9%) isolates in Brazil and in 4/38 (10.5%) in Mozambique. Both katG and inhA mutations were detected in respectively 1/22 (5%) and 2/38 (5.2%). The difference in the frequency of katG mutations in Brazil and Mozambique was statistically significant (P = 0.04). katG mutations were present in 68.8% (33/48) of patients previously treated with INH and 31.2% (15/48) of patients without previous INH. This difference was not statistically significant (P = 0.223). CONCLUSION: INH mutations varied geographically; molecular DST can be used to guide and accelerate decision making in the use of ETH or high doses of INH.