Original Research

False rifampicin resistant results using Xpert MTB/RIF on urine samples in hospitalised HIV-infected patients

Charlotte Schutz, Amy Ward, Rosie Burton, Mark P. Nicol, Liz Blumenthal, Graeme Meintjes, Andrew D. Kerkhoff
Southern African Journal of HIV Medicine | Vol 20, No 1 | a978 | DOI: https://doi.org/10.4102/sajhivmed.v20i1.978 | © 2019 Charlotte Schutz, Amy Ward, Rosie Burton, Mark P Nicol, Liz Blumenthal, Graeme Meintjes, Andrew D Kerkhoff | This work is licensed under CC Attribution 4.0
Submitted: 05 April 2019 | Published: 28 August 2019

About the author(s)

Charlotte Schutz, Wellcome Centre for Infectious Diseases Research in Africa (CIDRI-Africa), Institute of Infectious Disease and Molecular Medicine (IDM) and Department of Medicine, University of Cape Town, Cape Town, South Africa
Amy Ward, Wellcome Centre for Infectious Diseases Research in Africa (CIDRI-Africa), Institute of Infectious Disease and Molecular Medicine (IDM) and Department of Medicine, University of Cape Town, Cape Town, South Africa
Rosie Burton, GF Jooste Hospital, South Africa; and, Department of Medicine, University of Cape Town, Cape Town,, South Africa
Mark P. Nicol, Division of Medical Microbiology, University of Cape Town and National Health Laboratory Services, Cape Town, South Africa
Liz Blumenthal, Wellcome Centre for Infectious Diseases Research in Africa (CIDRI-Africa), Institute of Infectious Disease and Molecular Medicine (IDM) and Department of Medicine, University of Cape Town, Cape Town, South Africa
Graeme Meintjes, Wellcome Centre for Infectious Diseases Research in Africa (CIDRI-Africa), Institute of Infectious Disease and Molecular Medicine (IDM) and Department of Medicine, University of Cape Town, Cape Town, South Africa
Andrew D. Kerkhoff, Division of HIV, Infectious Diseases and Global Medicine at Zuckerberg San Francisco General Hospital and Trauma Center, Department of Medicine, University of California, San Francisco, California, United States


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Abstract

Background: A small proportion of false rifampicin resistant results have previously been reported using GeneXpert MTB/RIF version G4 on sputum samples; however, this has not been investigated for urine samples in HIV-associated tuberculosis (TB).

Objectives: We sought to determine the proportion of false rifampicin resistant results using Xpert MTB/RIF version G4 on urine samples among HIV-infected inpatients investigated for TB.

Methods: Hospitalised HIV-infected patients undergoing systematic TB testing from two cohorts in Cape Town, South Africa, were enrolled. All patients with ≥1 urine Xpert result available were included. Rifampicin resistant urine Xpert results were classified into three mutually exclusive groups: (1) true rifampicin resistance, (2) false rifampicin resistance or (3) unknown after review of available microbiologic and clinical data.

Results: Overall, 1171 patients were included, from whom a total of 1704 urine Xpert results were available on unconcentrated and/or concentrated urine samples. There were 416 samples positive for TB (24.4% [95% CI 22.4–26.5]), of which 43/413 (10.4% [95% CI 7.6–13.8]) were rifampicin resistant (after excluding three results that were falsely positive due to contamination). Of 43 rifampicin resistant Xpert results (among 40 patients), 30 were classified as true resistance, 11 as false resistance and 2 could not be classified. Excluding unclassifiable results, 30/41 results were confirmed as true-positive urine Xpert rifampicin resistance (positive predictive value: 73.2% [95% CI 57.1–85.8]).

Conclusion: Urine Xpert testing showed a high proportion of false rifampicin resistance results. Urine Xpert rifampicin resistant results should be interpreted cautiously and confirmed when possible.


Keywords

HIV; AIDS; Tuberculosis; Xpert; Rifampicin resistance; False resistance

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