Drug resistance pattern and mutation pattern in pediatric tuberculosis: Study from north India

Background: The emergence of multidrug-resistant MDR-TB and extensively drug-resistant XDR-TB are serious threats to global TB control. Molecular tests like GenoType MTBDRplus has revolutionized MDR-TB diagnosis by rapid detection of resistance, leading to early and appropriate management of DR-TB. Information about common mutations imparting resistance to RIF and INH, helps in understanding the disease epidemiology in various regions. The study was conducted to determine the genetic mutation in drug resistant tuberculosis in children less than 12 years with pulmonary or extrapulmonary tuberculosis.

Materials/methods: Retrospective analysis was done over a period of 54 months from January 2015 to June 2019 to study the resistance pattern and mutations present in DR-TB in children less than 12 years with suspected pulmonary or extrapulmonary tuberculosis using Hain's GenoType MTBDRplus VER 2.0.

Results: Over a period of 54 months, samples from 3461 patients with suspected TB were received for MGIT culture, out of which, 347 were positive for Mycobacterium tuberculosis. 250 of these 347 isolated were tested for drug resistance by Hain's GenoType MTBDRplus VER 2.0.61.1% were sensitive to isoniazid and rifampicin while 15.2% were DR-TB (38 out of 250). Out of these 38, 22 were MDR TB, 13 were isoniazid monoresistant (34.2%) and 3 were rifampicin monoresistant. The most common genotypic resistance for rifampicin was absence of rpoB WT8 band and presence of rpoB MUT 3 band (88%). 84.6% of the INH monoresistant isolates showed high level isoniazid resistant. All these isolates showed presence of katG MUT 1 band. On comparing Hain's GenoType MTBDRplus VER 2.0 with Xpert MTB/Rif Assay, most common mutation for rifampicin resistance at S531L which can be detected by Xpert MTB/Rif Assay (probe E). However, two cases with rifampicin resistance had mutation in codon region 509-513 and 513-519 which could be missed by Xpert MTB/Rif Assay.

Conclusions: We cannot solely rely on Xpert MTB/Rif Assay for detection of drug resistance due to the risk of missing the isoniazid monoresistance. GenoType MTBDRplus has revolutionized MDR-TB diagnosis by substantially reducing turn around time and leading to early management of DR-TB cases.