First experience with novel molecular diagnostic method for detection of M. tuberculosis and rifampicin resistance

Latvia has middle level notification rate of tuberculosis (TB) and ranks among 27 countries with the highest level of multi-drug resistant TB. Aim: To explore the sensitivity of a newly available molecular diagnostic method GeneXpert® (GX) in early detection of M.tuberculosis (MT) and rifampicine (RIF) resistance. Methods: Retrospective case control study. 360 respiratory samples (sputum and/or bronchial washings) from 320 subjects were tested with GX from 13/07/2010 (introduction of the method) till 01/11/2010. New pulmonary TB cases were analyzed. Results: 100 patients had new pulmonary TB. GX was positive in 68 cases, including 25 smear negative [Ziehl-Neelsen (ZN) and/or fluorescence microscopy] cases. Results of culture on liquid media (MGIT®) were available in 15 days, but on solid Levenstein-Jensen (LJ) media in 47. 2 patients with negative LJ culture were GX positive. Resistance of MT against RIF on LJ media were detected in 14 cases and matched in 3 cases also with MGIT® method (results available in 80 and 24 days respectively). In 6 cases out of 14 (40%) when RIF resistance detection concurred with LJ method, results with LJ were available in 68 days. 5 discordant cases (GX RIF resistant, LJ RIF sensitive) currently are extensively analyzed. Conclusions: In addition to conventional smear microscopy methods GeneXpert® improves the diagnostic of pulmonary TB and allows faster detection of RIF resistance.