Page 197 - SAHCS HIVMed Journal Vol 20 No 1 2019

Southern African Journal of HIV Medicine
ISSN: (Online) 2078-6751, (Print) 1608-9693
Page 1 of 10 Original Research

False rifampicin resistant results using Xpert MTB/RIF

on urine samples in hospitalised HIV-infected patients

Authors: Background: A small proportion of false rifampicin resistant results have previously been
Charlotte Schutz 1 reported using GeneXpert MTB/RIF version G4 on sputum samples; however, this has not
Amy Ward 1
Rosie Burton 2 been investigated for urine samples in HIV-associated tuberculosis (TB).
Mark P. Nicol 3
Liz Blumenthal Objectives: We sought to determine the proportion of false rifampicin resistant results using
1
Graeme Meintjes 1 Xpert MTB/RIF version G4 on urine samples among HIV-infected inpatients investigated
Andrew D. Kerkhoff 4 for TB.
Affiliations: Methods: Hospitalised HIV-infected patients undergoing systematic TB testing from two
1 Wellcome Centre for cohorts in Cape Town, South Africa, were enrolled. All patients with ≥1 urine Xpert result
Infectious Diseases Research available were included. Rifampicin resistant urine Xpert results were classified into three
in Africa (CIDRI-Africa),
Institute of Infectious Disease mutually exclusive groups: (1) true rifampicin resistance, (2) false rifampicin resistance or
and Molecular Medicine (3) unknown after review of available microbiologic and clinical data.
(IDM) and Department of
Medicine, University of Results: Overall, 1171 patients were included, from whom a total of 1704 urine Xpert results
Cape Town, Cape Town, were available on unconcentrated and/or concentrated urine samples. There were 416 samples
South Africa 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
2 GF Jooste Hospital;
Department of Medicine, contamination). Of 43 rifampicin resistant Xpert results (among 40 patients), 30 were classified
University of Cape Town, as true resistance, 11 as false resistance and 2 could not be classified. Excluding unclassifiable
Cape Town, South Africa results, 30/41 results were confirmed as true-positive urine Xpert rifampicin resistance
(positive predictive value: 73.2% [95% CI 57.1–85.8]).
3 Division of Medical
Microbiology, University of Conclusion: Urine Xpert testing showed a high proportion of false rifampicin resistance
Cape Town and National results. Urine Xpert rifampicin resistant results should be interpreted cautiously and confirmed
Health Laboratory Services,
Cape Town, South Africa when possible.
Keywords: HIV; AIDS; Tuberculosis; Xpert; Rifampicin resistance; False resistance.
4 Division of HIV, Infectious
Diseases and Global
Medicine at Zuckerberg
San Francisco General Introduction
Hospital and Trauma Center, Tuberculosis (TB) remains the leading cause of death in people living with HIV, contributing
Department of Medicine,
1
University of California, to one-in-three AIDS-related deaths. Timely diagnosis of TB in such patients remains
San Francisco, United States challenging because of non-specific presentations and disseminated disease. 2,3,4 Gene Xpert
MTB/RIF, an automated nucleic acid amplification test, is capable of providing results in a
Corresponding author:
Andrew Kerkhoff, few hours and represents an important breakthrough for diagnosing HIV-associated TB.
andrew.kerkhoff@ucsf.edu Importantly, Xpert also rapidly detects rifampicin resistance, without need for an additional
sample or cartridges. It has been endorsed by the World Health Organization (WHO) since
Dates: 2010. Sputum Xpert (or Xpert Ultra where available) is currently recommended by the WHO
Received: 05 Apr. 2019
Accepted: 24 May 2019 as the initial diagnostic test in patients with suspected HIV-associated TB or multi-drug
Published: 28 Aug. 2019 resistant (MDR) TB. In those with microbiologically confirmed TB, Xpert MTB/RIF is also
5
recommended by the WHO as a first-line assay for the rapid detection of rifampicin-resistance.
It is therefore an important tool in tackling the growing global health challenge of drug
resistant (DR)-TB. However, the WHO does not currently have a recommendation regarding
the use of Xpert MTB/RIF in urine owing to an insufficient amount of data on the performance
and utility of this assay in urine specimens. 6

In concordance with WHO guidelines, sputum Xpert was implemented as the initial diagnostic
Read online: evaluation in those with suspected TB and DR-TB in South Africa as well as other countries and
7
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mobile device How to cite this article: Schutz C, Ward A, Burton R, et al. False rifampicin resistant results using Xpert MTB/RIF on urine samples in
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to read online. hospitalised HIV-infected patients. S Afr J HIV Med. 2019;20(1), a978. https://doi.org/10.4102/sajhivmed.v20i1.978
Copyright: © 2019. The Authors. Licensee: AOSIS. This work is licensed under the Creative Commons Attribution License.
http://www.sajhivmed.org.za 190 Open Access