Missed phenotypic drug resistance in pediatric tuberculosis: A cause of concern in a resource-limited setting

Background Multi-drug resistance (MDR) in pediatric tuberculosis (TB) is a growing global threat. Unavailability of conventional or molecular drug susceptibility test (DST) in resource-limited settings often impede the determination of the extent of first line anti-tubercular drugs deployed in national programs. Materials and method Pulmonary and extra pulmonary specimens were collected from clinically suspected pediatric TB cases, who were microbiologically confirmed. Resistance to first-line anti-TB was detected by 1% proportion method. KatG315 and inhA-15 genes were amplified by PCR and detection of mutations were done by sequencing. Genotypic resistance for rifampicin was detected by Xpert MTB/RIF assay (Cepheid Inc., Sunnyvale, California). Results Fifty-one cases of pediatric tuberculosis were confirmed microbiologically. Resistance to isoniazid, streptomycin, rifampicin and ethambutol were 5 (14%), 4 (11%), 2 (5.5%) and 2 (5.5%) respectively by 1% proportion method. Genotypic Rifampicin and isoniazid resistance was found in 2 (5.5%) and 7 (14%) samples respectively. Conclusion Existing genotypic methods, detect targeted mutations conferring rifampicin resistance, however isoniazid (INH) resistance often go undetected. Since the resistance to pivotal anti-TB drugs are often encoded by multiple genes which may not be targeted by widely available molecular tests, discrepancies in molecular and culture-based DST reports should be interpreted with caution.