GeneXpert MTB/RIF Testing in the Management of Patients with Active Tuberculosis; A Real Life Experience from Saudi Arabia

BACKGROUND: GeneXpert MTB/RIF is a real-time PCR assay with established diagnostic performance in pulmonary and extra-pulmonary forms of tuberculosis. The aim of this study was to assess the contribution of GeneXpert MTB/RIF assay to the management of patients with any form of active tuberculosis in a single large tertiary center in Saudi Arabia, with a special focus on the impact on time to start of antituberculous therapy compared with Ziehl-Neelsen (ZN) smears and mycobacterial cultures. MATERIALS AND METHODS: Clinical, radiological and laboratory records for all patients who were commenced on antituberculous therapy between March 2011 and February 2013 were retrospectively reviewed. RESULTS: A total of 140 patients were included, 38.6% of which had pulmonary tuberculosis. GeneXpert MTB/RIF was requested for only 39.2% of patients and was the only reason for starting antituberculous therapy for only 12.1%. The median time to a positive GeneXpert MTB/RIF result was 0 days (IQR 3) compared with 0 day (IQR 1) for smear microscopy (P > 0.999) and 22 days (IQR 21) for mycobacterial cultures (P < 0.001). No patients discontinued antituberculous therapy because of a negative GeneXpert MTB/RIF result. CONCLUSIONS: In a setting wherein physicians are highly experienced in the diagnosis and treatment of tuberculosis, GeneXpert MTB/RIF was remarkably under-utilized and had only a limited impact on decisions related to starting or stopping antituberculous therapy. Cost-effectiveness and clinical utility of routine testing of all smear-negative clinical samples submitted for tuberculosis investigations by GeneXpert MTB/RIF warrant further study.

Evaluation of direct detection of Mycobacterium tuberculosis complex in respiratory and non-respiratory clinical specimens using the Cepheid Gene Xpert[registered sign] system

To compare the sensitivity and specificity of Cepheid Gene Xpert[registered sign], MTB/RIF assay for direct detection of Mycobacterium tuberculosis complex [MTBC] and rifampin [RIF] resistance with conventional methods in respiratory and non-respiratory clinical specimens. We used a cross sectional design to evaluate a diagnostic test at the TB Section of the Division of Microbiology, Central Military Laboratory and Blood Bank, Prince Sultan Military Medical City, Riyadh, Kingdom of Saudi Arabia from October 2011 to January 2012. The detection of MTBC and RIF resistance using the Xpert[registered sign] MTB/RIF assay was assessed in 239 [172 respiratory, and 67 non respiratory] specimens received from 234 patients suspected of TB, and compared with conventional smear microscopy and culture methods. Out of the 239 specimens investigated, 62 [25.9%] were MTBC positive by culture, while 59 [24.6%] were positive by Xpert[registered sign] assay. Three samples showed false negative Xpert[registered sign] results. Compared with the culture, the Xpert[registered sign] assay achieved 95.4% [95% CI: 89-100%] sensitivity, and 100% [95% CI: 93.6-100%] specificity for respiratory samples, while the sensitivity for non-respiratory specimens was 94.4% [95% CI: 90.2-98.5], and the specificity for non-respiratory specimens was 100% [95% CI: 95.8-100%]. Overall, a 95.2% [95% CI: 87.6-100] sensitivity, and 100% [95% CI: 92.4-100%] specificity, was observed for the Xpert[registered sign] MTB/RIF assay compared with conventional methods for MTBC detection. The gene Xpert[registered sign] MTB/RIF assay is a helpful tool for the detection of MTBC and RIF resistance in respiratory and non-respiratory clinical samples with a high sensitivity and specificity within 2 hours as compared with conventional methods, which took a much longer time