Brief Report

Diagnosis of rifampicin-resistant tuberculosis: Discordant results by diagnostic methods

Winnie Mwanza, Deborah Milimo, Maureen M. Chilufya, Nkatya Kasese, Maina C. Lengwe, Stembiso Munkondya, Petra de Haas, Helen Ayles, Monde Muyoyeta
African Journal of Laboratory Medicine | Vol 7, No 2 | a806 | DOI: https://doi.org/10.4102/ajlm.v7i2.806 | © 2018 Winnie Mwanza, Deborah Milimo, Maureen Moyo Chilufya, Nkatya Kasese, Maina Cheeba Lengwe, Stembiso Munkondya, Petra De Haas, Helen Ayles, Monde Muyoyeta | This work is licensed under CC Attribution 4.0
Submitted: 09 April 2018 | Published: 06 December 2018

About the author(s)

Winnie Mwanza, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Deborah Milimo, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Maureen M. Chilufya, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Nkatya Kasese, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Maina C. Lengwe, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Stembiso Munkondya, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia
Petra de Haas, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia; and,Department of Infectious and Tropical diseases, London School of Hygiene and Tropical Medicine, Bloomsburg, London, United Kingdom
Helen Ayles, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia; and,Department of Infectious and Tropical diseases, London School of Hygiene and Tropical Medicine, Bloomsburg, London, United Kingdom
Monde Muyoyeta, Zambia AIDS Related Tuberculosis (ZAMBART) Project, School of Medicine, University of Zambia, Lusaka, Zambia

Abstract

The performance of the Xpert© MTB/RIF and MTBDRplus assays for the detection of rifampicin resistant Mycobacterium tuberculosis was compared to culture-based drug susceptibility testing in 30 specimens with rifampicin-resistant and rifampicin-indeterminate Xpert MTB/RIF results collected between March 2012 and March 2014. Xpert MTB/RIF and MTBDRplus were 100% sensitive and 100% concordant for rifampicin resistance detection, but 3 of 13 samples (23%) positive for rifampicin resistance on Xpert MTB/RIF and MTBDRplus were negative for rifampicin resistance on mycobacteria growth indicator tube drug susceptibility testing. Specificity was 72% for Xpert MTB/RIF and 80% for MTBDRplus. Positive predictive value for Xpert MTB/RIF for multidrug resistant tuberculosis was 47.8% for new patients and 77.8% for previously treated patients; negative predictive value was 100% for both new and previously treated patients. The discordant rifampicin resistance test results indicate a need to fully characterise circulating rifampicin resistant Mycobacterium tuberculosis strains in Zambia and to inform the development of guidelines for decision-making in relation to diagnosis of drug-resistant tuberculosis.

Keywords

RpoB; silent mutations; Xpert MTB RIF; MTBDRplus; DS; Zambia

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