Case report of a false positive result of the Xpert® MTB/RIF assay for rifampicin resistance in Mycobacterium tuberculosis complex.

In the present case, we report a false positive result for the detection of rifampicin (RIF) resistance by the Xpert® MTB/RIF assay, version G4.Miliary Mycobacterium tuberculosis infection (miliary TB) was suspected in a 50-year old Angolan woman. Imaging of the thorax and abdomen displayed diffuse lesions. The Xpert® MTB/RIF assay conducted on the broncho-alveolar lavage (BAL) fluid was positive for TB and positive for RIF resistance. Confirmatory molecular tests and the phenotypic drug susceptibility determination supported the diagnosis of TB but not RIF resistance. The patient was treated successfully with a conventional therapeutic scheme. Because, the Xpert® MTB/RIF assay allows the simultaneous detection of TB and RIF resistance, the World Health Organisation (WHO) recommends its use as initial diagnostic test, over microscopy, culture and phenotypic drug susceptibility testing. Even though specificity of the Xpert® MTB/RIF assay version G4 is high, false positive test results remain possible and have to be considered for the interpretation of the RIF resistance detection by Xpert® MTB/RIF assay.