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Huang W, Lee MKT, Sin ATK, Nazari RS, Chua SY, Sng LH. Evaluation of Xpert MTB/RIF ultra assay for detection of Mycobacterium tuberculosis and rifampicin resistance. Pathology 2023:S0031-3025(23)00116-2. [PMID: 37268484 DOI: 10.1016/j.pathol.2023.03.002] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2022] [Revised: 01/05/2023] [Accepted: 03/14/2023] [Indexed: 06/04/2023]
Abstract
Tuberculosis (TB) is a public health challenge globally, and molecular testing is recommended to expedite diagnosis. Concerns that Xpert MTB/RIF assay (Xpert) may be less sensitive when testing paucibacillary samples led to the development of the Xpert MTB/RIF Ultra assay (Ultra). We evaluated the performance of Ultra against Xpert on clinical samples sent to the national reference laboratory in Singapore. In total, 149 samples collected between January 2019 and November 2020 were analysed. Mycobacterium tuberculosis complex (MTBC) was isolated from 55 cultures. Using culture as the reference standard, Ultra demonstrated higher sensitivity (96.4% vs 85.5%) and marginally lower specificity (88.3% vs 89.4%) compared to Xpert in the full cohort. When considering only paucibacillary specimens such as extrapulmonary and smear-negative samples, similar results were obtained. Reclassifying Ultra trace results (low levels of MTB are detected but no rifampicin resistant result is detected) as negative in the full cohort led to a decrease in sensitivity by 10.9% and a marginal increase in specificity by 1.1%. In instances of low bacillary load, Ultra also identified rifampicin resistance more accurately than Xpert, when corroborated against other methods such as broth microdilution, line probe assay and whole genome sequencing (WGS). One isolate tested rifampicin-resistant using Xpert and Ultra, but was phenotypically susceptible and WGS demonstrated the presence of the silent mutation Thr444Thr. Ultra is more sensitive than Xpert in the detection of MTBC and rifampicin resistance in our local setting. Nevertheless, the results of molecular testing should still be correlated with phenotypic studies.
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Affiliation(s)
- Wenjie Huang
- Central Tuberculosis Laboratory, Department of Microbiology, Singapore General Hospital, Singapore.
| | - Melody Kee Tai Lee
- Central Tuberculosis Laboratory, Department of Microbiology, Singapore General Hospital, Singapore
| | - Amanda Teo Kai Sin
- Central Tuberculosis Laboratory, Department of Microbiology, Singapore General Hospital, Singapore
| | | | - Syn Yu Chua
- Central Tuberculosis Laboratory, Department of Microbiology, Singapore General Hospital, Singapore
| | - Li-Hwei Sng
- Central Tuberculosis Laboratory, Department of Microbiology, Singapore General Hospital, Singapore
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Ssengooba W, de Dieu Iragena J, Komakech K, Okello I, Nalunjogi J, Katagira W, Kimuli I, Adakun S, Joloba ML, Torrea G, Kirenga BJ. Discordance of the Repeat GeneXpert MTB/RIF Test for Rifampicin Resistance Detection Among Patients Initiating MDR-TB Treatment in Uganda. Open Forum Infect Dis 2021; 8:ofab173. [PMID: 34189166 PMCID: PMC8223903 DOI: 10.1093/ofid/ofab173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Accepted: 03/31/2021] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The Global Laboratory Initiative (GLI) guidelines recommend repeat for GeneXpertMTB/RIF (XpertMTB/RIF) in patients with a low pretest probability of rifampicin resistance (RR). METHODS This was a cross-sectional study using results of sputum specimens collected from participants screened for the STREAM 2 trial. We recruited all patients with XpertMTB/RIF RR-TB detected who were referred for RR/multidrug-resistant (MDR) TB treatment initiation at Mulago National Referral Hospital, Kampala, between September 2017 and October 2019. At baseline, smear microscopy, repeat XpertMTB/RIF, Xpert Ultra, and MTBDRplus assays were done on sputum specimens. Culture-based drug susceptibility testing (DST) was performed on discordant specimens. We analyzed the prevalence and factors associated with discordance between initial and repeat XpertMTB/RIF RR and false XpertMTB/RIF RR. False XpertMTB/RIF RR was defined as no RR detected by any of Xpert Ultra, LPA, or culture DST (reference comparator). RESULTS A total of 126/130 patients had repeat XpertMTB/RIF results, of whom 97 (77.0%) had M. tuberculosis detected, 81 (83.5%) had RR detected, and 1 (1.0%) had RR indeterminate. The prevalence of discordant XpertMTB/RIF RR was 15/96 (15.6%), whereas false XpertMTB/RIF RR prevalence was 10/96 (10.4%).Low-bacillary load sputum specimens were more likely to have discordant XpertMTB/RIF RR and false XpertMTB/RIF RR results (adjusted odds ratio [aOR], 0.04; 95% CI, 0.00-0.37; P = .01; aOR, 0.02; 95% CI, 0.01-0.35; P = .01, respectively). CONCLUSIONS Our findings show a high false-positive rifampicin resistance rate in low-TB burden patients, which calls for repeat testing in order to prevent unnecessary prescription of anti-MDR-TB therapy.
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Affiliation(s)
- Willy Ssengooba
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
- Mycobacteriology (BSL-3) Laboratory, Department of Medical Microbiology, Makerere University, Kampala, Uganda
| | - Jean de Dieu Iragena
- Communicable Diseases Cluster, HIV/TB and Hepatitis Programme, World Health Organization Regional Office for Africa, Brazzaville, Congo
| | - Kevin Komakech
- Mycobacteriology (BSL-3) Laboratory, Department of Medical Microbiology, Makerere University, Kampala, Uganda
| | - Iginitius Okello
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
| | - Joanitah Nalunjogi
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
| | - Winceslaus Katagira
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
| | - Ivan Kimuli
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
| | - Susan Adakun
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
- National Tuberculosis Treatment Unit, Mulago Hospital, Kampala, Uganda
| | - Moses L Joloba
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
- Mycobacteriology (BSL-3) Laboratory, Department of Medical Microbiology, Makerere University, Kampala, Uganda
| | - Gabriela Torrea
- Unit of Mycobacteriology, Department of Biomedical Sciences, Institute of Tropical Medicine, Antwerp, Belgium
| | - Bruce J Kirenga
- College of Health Sciences, Makerere University Lung Institute, Kampala, Uganda
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