[Evaluation of Xpert® MTB/RIF technique for Mycobacterium tuberculosis complex detection in extra-respiratory specimens]

Abstract

Extra-pulmonary tuberculosis (TB) represents the 26.2% of total TB cases in Chile. Culture is the gold standard method, but the process is extremely slow. Xpert®MTB/RIF technique detects Mycobacterium tuberculosis complex (MTBc) through real time PCR in less than 3 h. However, it has been validated only for respiratory specimens. We aimed to determine the performance of Xpert®MTB/RIF test in detecting MTBc in extra-respiratory specimens compared with a combined gold standard consisting in a positive (liquid and solid) mycobacterial culture and/or a positive validated molecular method (q-RPC, Cobas®TaqMan®-MTB). Fifty extra-respiratory specimens were analyzed, from which 25 were positive and 25 negative for MTBc based on the combined gold standard. The 25 positive specimens had a positive result by Xpert®MTB/RIF; from the 25 negative specimens, 24 had a negative result and one had a positive result. We obtained an overall concordance of 98% between Xpert®MTB/RIF and the combined gold standard. Xpert®MTB/RIF test was able to detect 12 smear-negative specimens and 3 culture-negative specimens, all of them corresponding to extra-pulmonary TB cases. Xpert®MTB/RIF showed similar sensitivity to q-RPC in detecting MTBc in extra-respiratory specimens. This procedure allowed a substantial reduction in the time of diagnosis.