The Xpert® MTB/RIF assay in routine diagnosis of pulmonary tuberculosis: A multicentre study in Lithuania

Abstract

Introduction: Drug-resistant tuberculosis (TB) is an important public health problem in Lithuania with MDR rates in new cases reaching 11% in 2012. Currently available diagnostic tools are not fully adequate for an accurate and rapid result for diagnosis of TB and MDR-TB.

Objectives: To evaluate the performance of Xpert(®) MTB/RIF assay for an early diagnosis of TB and detection of rifampicin (RIF) resistance in routine settings in Lithuania.

Methods: A total of 833 individual respiratory samples obtained from patients previously treated for TB and MDR-TB contacts were tested using the Xpert MTB/RIF assay. Performance characteristics of the assay for TB and RIF resistance detection were calculated using culture and phenotypical DST results as a gold standard.

Results: The overall sensitivity and specificity of the Xpert MTB/RIF assay for TB detection were 93.7% and 91.7%, respectively with the sensitivity for smear-negative specimens reaching 82.5%. Resistance to RIF was detected in 81 (20.7%) primary specimens with no false negative results; there were 4/225 (1.8%) false-positives among strains sensitive to rifampicin. Overall sensitivity and specificity of the molecular assay for detection of RIF resistance calculated against phenotypic DST results were 100% and 98.2%, respectively.

Conclusions: Our results demonstrate very good performance of the Xpert MTB/RIF assay for the detection of TB and RIF resistance on primary respiratory specimens. It provides strong evidence that implementation of the assay for routine laboratory diagnosis in high drug-resistance settings may improve and facilitate TB diagnosis.

Keywords: Drug susceptibility testing; Mycobacterium tuberculosis; Nucleic acid amplification test; Xpert MTB/RIF assay.