Three year evaluation of Xpert MTB/RIF in a low prevalence tuberculosis setting: A Scottish perspective

Summary Objectives Xpert MTB/RIF (Cepheid) is a rapid molecular assay shown to be sensitive and specific for pulmonary tuberculosis (TB) diagnosis in highly endemic countries. We evaluated its diagnostic performance in a low TB prevalence setting, examined rifampicin resistance detection and quantit...

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Bibliographic Details
Published in:The Journal of infection 2017-05, Vol.74 (5), p.466-472
Main Authors: Parcell, Benjamin J, Jarchow-MacDonald, Anna A, Seagar, Amie-Louise, Laurenson, Ian F, Prescott, Gordon J, Lockhart, Michael
Format: Article
Language:English
Subjects:
Antibiotics, Antitubercular - pharmacology
Early Diagnosis
Humans
Infectious Disease
Molecular testing
Molecular Typing - methods
Mycobacterium tuberculosis
Mycobacterium tuberculosis - drug effects
Mycobacterium tuberculosis - genetics
Nucleic acid amplification
Predictive Value of Tests
Retrospective Studies
Rifampin - pharmacology
Scotland
Tuberculosis
Tuberculosis - diagnosis
Tuberculosis - microbiology
Xpert MTB/RIF
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Summary:Summary Objectives Xpert MTB/RIF (Cepheid) is a rapid molecular assay shown to be sensitive and specific for pulmonary tuberculosis (TB) diagnosis in highly endemic countries. We evaluated its diagnostic performance in a low TB prevalence setting, examined rifampicin resistance detection and quantitative capabilities predicting graded auramine microscopy and time to positivity (TTP) of culture. Methods Xpert MTB/RIF was used to test respiratory samples over a 3 year period. Samples underwent graded auramine microscopy, solid/liquid culture, in-house IS 6110 real-time PCR, and GenoType MTBDRplus (HAIN Lifescience) to determine rifampicin and/or isoniazid resistance. Results A total of 2103 Xpert MTB/RIF tests were performed. Compared to culture sensitivity was 95.8%, specificity 99.5%, positive predictive value (PPV) 82.1%, and negative predictive value (NPV) 99.9%. A positive correlation was found between auramine microscopy grade and Xpert MTB/RIF assay load. We found a clear reduction in the median TTP as Xpert MTB/RIF assay load increased. Rifampicin resistance was detected. Conclusions Xpert MTB/RIF was rapid and accurate in diagnosing pulmonary TB in a low prevalence area. Rapid results will influence infection prevention and control and treatment measures. The excellent NPV obtained suggests further work should be carried out to assess its role in replacing microscopy.
ISSN:0163-4453
1532-2742
DOI:10.1016/j.jinf.2017.02.005