Evaluate “Rifampicin Resistance” as Surrogate Marker for Rapid Detection of MDR-TB Using Real-Time PCR Directly on FNAC Samples of Tuberculous Lymphadenitis

Abstract

Background: India has the dubious distinction of having second largest burden of MDR-TB cases in the world. According to WHO, MDR-TB is defined as resistance to isoniazid and rifampicin, the two most important drugs for treatment of TB. “Rifampicin resistance” is recommended as surrogate marker for MDR-TB by WHO, as at least, 90% of all rifampicin-resistant clinical isolates are also found resistant to isoniazid. Localization of  genetic alterations in the 81-bp “Rifampicin Resistance-Determining Region” of rpoB gene in 96% of rifampicin resistant strains make it particularly amenable for early detection of MDR-TB by molecular techniques like Real-Time PCR. Aim: Evaluation of “rifamipicin resistance” as surrogate marker for rapid detection of MDR-TB using Real-Time PCR directly on FNAC samples of tuberculous lymphadenitis (TBLN). Materials and Methods: Eighty cases of TBLN undergoing anti-tubercular treatment (ATT) and 10 lymphadenitis cases of non-tuberculous origin (controls) were included in the study. To evaluate “rifamipicin resistance” as surrogate marker for rapid detection of MDR-TB, Real-Time PCR and conventional Drug Susceptible Testing (DST) were carried out. Results: Eighteen samples were identified as MDR-TB cases by DST. Real-Time PCR picked up mutated ropB gene in 17 cases out of these 18 MDR-TB cases. Conclusion: “Rifampicin resistance” is an efficient surrogate marker for timely detection of MDR-TB using rapid, accurate and sensitive molecular technique like Real-Time PCR.