The evaluation of the Xpert MTB/RIF in the diagnosis of mycobacterium tuberculosis complex and detection of rifampicin resistance in extrapulmonary (pleural and ascitic) fluid samples received for routine immunophenotypic analysis in a high-burden tuberculosis setting

• Main Author: Kilfoil, Kim Michelle
• Format: Others
• Language: en
• Published: 2016
• Subjects: Mycobacterium tuberculosis; Tuberculosis; Rifampin
• Online Access: http://hdl.handle.net/10539/19955

A research report submitted to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Medicine in the branch of Haematology. Johannesburg, 2015. === Introduction: The Gene Xpert MTB/Rif assay (Xpert) is a nucleic acid amplification technique that has been studied in the diagnosis of both pulmonary and, to a lesser extent, extrapulmonary tuberculosis (TB). This study was performed in the National Health Laboratory Services (NHLS) laboratory at Charlotte Maxeke Hospital which services a population with a high prevalence of Mycobacterium Tuberculosis Complex (MTBC) infection. The study aimed to develop a protocol for the processing of pleural and ascitic fluid samples to be run on Xpert for MTBC diagnosis, to evaluate the sensitivity and specificity of the Xpert assay as compared to the gold standard MTBC culture assays and to assess the utility of the Xpert assay as part of the diagnostic algorithm for fluid samples received in high prevalence MTBC laboratories. Materials and methods: A total of 392 pleural and ascitic fluid specimens were received for routine immunophenotypic analysis between August 2012 and February 2013 at the NHLS flow cytometry laboratory in Charlotte Maxeke hospital. Of these specimens, 229 had sufficient residual volume (>0.5ml) after routine immunophenotypic analysis to be tested on Xpert. Specimens were processed as per the manufacturer’s guidelines for pulmonary specimens and results were compared to the gold standard culture for Mycobacterium tuberculosis. Results: Xpert positivity was detected in 8.7% (20/229) of the total specimens. Only 43% (99/229) of these specimens were submitted for concurrent MTBC liquid culture (Mycobacterium Growth Indicator tube, MGIT) testing based on the laboratory information system history. Positivity on Xpert was shown in 9% (9/99) of specimens compared to 17% (17/99) on MGIT. One false positive was detected on Xpert. More than half of the specimens, 57% (130/229) were not referred for concurrent MTBC culture. The Xpert detected MTBC in 8.5% (11/130) of these specimens, with 1 Rifampicin resistant case identified. Xpert sensitivity and specificity in this study were 50% (CI:26-75%) and 99% (CI:91-100%) respectively Conclusion: The sensitivity and specificity of Xpert in this study was comparable to that found in other studies performed on fluid samples. Importantly, this study demonstrates that in a high burden HIV/TB setting like South Africa, more than 50% of fluid specimens referred for immunophenotypic analysis to exclude lymphoma are not referred for concurrent MTBC culture testing. Incorporation of Xpert into the laboratory diagnostic algorithm (LDA) in the immunophenotypic laboratory would, therefore, have a number of benefits, improving overall patient work-up and care. Implementation and policy uptake, however, would require a full costing analysis as Xpert testing would be performed in addition to, and not instead of, routine testing.