Assessment of diagnostic accuracy of Gene Xpert MTB/RIF in diagnosis of suspected retreatment pulmonary tuberculosis patients

BackgroundRetreatment cases of tuberculosis are reemerging as public and global health concerns, not only for dissemination of infection but for their multidrug resistant behavior as well, comprising an important challenge for National Tuberculosis Control Programs. Gene Xpert MTB/RIF is an automated molecular test for synchronized detection of tuberculosis and rifampicin resistance, recommended by the World Health Organization. This study was designed to assess the performance of single-sputum Gene Xpert MTB/RIF assay against the Ziehl–Neelsen smear, traditional culture and MGIT 960 in diagnosing suspected retreatment pulmonary tuberculosis cases and rifampicin resistance.Subjects and methodsFifty-eight patients were enrolled in this cross-sectional study from two Egyptian tertiary care hospitals. The patients were selected fulfilling clinical criteria of suspected retreatment TB. Early-morning sputum specimens were collected, decontamination liquefaction technique was done, the specimen was divided into four portions, the first and second portions were for the Ziehl–Neelsen smear and cultivation on the Löwenstein Jensen media. The third portion was processed in Gene Xpert MTB/RIF. The fourth part was used for confirmation of rifampicin susceptibility testing results by MGIT 960.ResultsGene Xpert MTB/RIF showed sensitivity, specificity and accuracy of 98.15%, 75% and 96.55% respectively in detection of mycobacterium tuberculosis. Regarding rifampicin mono-resistance, it carried the best sensitivity and specificity of 100% equal to that of reference test MGIT 960.ConclusionGene Xpert MTB/RIF is a sensitive, specific and accurate test for both diagnosis of retreatment MTB and rifampicin resistance. Finally the authors recommend restandardization of reference test with Gene Xpert MTB/RIF to obtain more valid results