Mycobacterium Tuberculosis Complex Indicates Evolutionarily Recent Global Dissemination.
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Date
2016-06
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Addis Ababa Universty
Abstract
The lack of simple, accurate and rapid diagnostics is a major hindrance to TB control
efforts, especially in developing countries including Ethiopia where sputum smear
microscopy is the mainstay of diagnosis. Therefore, the need for rapid and accurate
diagnostics is crucial. The new Speed-oligo Direct Mycobacterium tuberculosis (SODMT)
assay is a novel assay which is based on multiplex PCR combined with dipstick
hybridization that allows amplification of 16S rRNA and IS6110 to detect genus
Mycobacterium and Mycobacterium tuberculosis complex from respiratory samples,
respectively. The objective of the study is to evaluate the performance of the new SODMT
assay in relation to conventional microscopic and culture methods and Xpert
MTB/RIF assay for the detection of M. tuberculosis complex directly from sputum
samples in SNNPR, Ethiopia. A total of 145 sputum samples were included in the
evaluation of SO-DMT assay. One sample per patient was decontaminated by NALCNaOH
method to perform Ziehl-Neelsen stain, culture and SO-DMT assay. One hundred
nine of the sputum specimens were also tested by Xpert MTB/RIF assay. The sensitivity,
specificity, positive predictive value and negative predictive value of SO-DMT assay for
detection of MTBC were 96%, 97.8%, 99% and 91.7%, respectively with reference to
culture. The corresponding values after resolution of discrepant results with culture and
clinical data were 96% (100% in smear-positives and 89.5% in smear-negatives), 100%,
100% and 91.7% (100% in smear-positives and 90.5% in smear-negatives), respectively.
The concordance between SO-DMT assay results and culture had a Cohen’s kappa index
of 0.921 (SE, 0.035), indicating excellent concordance. The sensitivity of both SO-DMT
and Xpert MTB/RIF assays was 94.8% (100% in smear-positives and 87.1% in smearnegatives).
The specificity of SO-DMT and Xpert MTB/RIF assays were 100% and
93.8% (100% in smear-positives and 93% in smear-negatives), respectively. Therefore,
SO-DMT has a good sensitivity and specificity in smear-positive and smear negative
specimens. It's use can avoid the need to wait for culture results. This assay might be a
good alternative to real-time PCR assays for laboratories not equipped with real-time
PCR instruments.
Key words: Löwenstein-Jensen culture, SO-DMT assay, Xpert MTB/RIF assay, Ziehl-
Neelsen staining
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Keywords
Löwenstein-Jensen culture, SO-DMT assay, Xpert MTB/RIF assay, Ziehl- Neelsen staining