Direct and early detection of Mycobacterium tuberculosis complex and rifampicin resistance from sputum smears

SETTING: Four district DOTS centres in Sikkim, India. OBJECTIVE: Direct and early detection of Mycobacterium tuberculosis complex and rifampicin (RMP) susceptibility using the INNO-LiPA Rif.TB assay. DESIGN: DNA was extracted from 44 inactivated acid-fast bacilli-positive sputum slides using the Gen Elute bacterial genomic DNA kit. Eluted DNA were ethanol precipitated. The LiPA kit detected RMP susceptibility by detection of mutation in the 81 base pair (bp) rpoB gene. Culture of sputum from the same person was used for drug susceptibility testing for RMP using the proportion method. RESULTS: Amplification of 88.6% (39 slides) was achieved from DNA extracted using kits (66.7% for 1+, 81.8% for 2+ and 100% for 3+ slides). Hybridisation using the LiPA kit was applied to 31 amplified products. There was a concordance of 96.8% (24 RMP-resistant and 6 RMP-susceptible samples) and discordance of 3.2% (one sample resistant using the proportion method and susceptible on LiPA) between LiPA and the proportion method. CONCLUSION: LiPA proved useful on DNA extracted from smear-positive slides. Appropriate treatment regimen could be decided early. Slide smear preparation could replace sputum transport in cetylpyridinium chloride, reducing biohazard and thereby controlling the transmission of multidrug-resistant tuberculosis in the community.