Comparative Performance Between Xpert Mtb/Rif Assay, Led Fluorescence Microscopy, and Zn Light Microscopy for Detection of Mycobacterium Tuberculosis In Sputum Samples in Addis Ababa, Ethiopia
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Date
2014-05
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Addis Ababa University
Abstract
Background: In Ethiopia, the main tool used to diagnosis pulmonary tuberculosis is Ziehl-
Neelsen microscopy. The emergence of drug-resistant forms of tuberculosis which needs more
resources to detect, to successfully treat and effectively reduce the burden is among the top
challenges in the country. Tuberculosis case detection among vulnerable population groups
including children, HIV positives and other high risk groups remains low due to insensitive
diagnostic tools. Due to its low sensitivity, Ziehl-Neelsen microscopy does not detect all positive
TB cases among TB suspects; as a result tuberculosis transmission by false negative cases
increases. Therefore, there is a need to assess the incremental value of new diagnostic tool like
Xpert MTB/RIF assay and Light Emitted Diode Fluorescent microscopy for tuberculosis
detection in our setting.
Objective of the study: To determine the performance of Xpert MTB/RIF assay in comparison
with Light Emitted Diode Fluorescent microscopy and Ziehl-Neelsen smear microscopy for
detection of Mycobacterium Tuberculosis in sputum samples in Addis Ababa.
Methods and Materials: A prospective cross-sectional study from December, 2013 to April,
2014 was conducted in AAHRL to compare the performance of light emitting diode fluorescent
microscopy (LED-FM), Xpert MTB/RIF assay and Ziehl-Neelsen(ZN) smear microscopy in the
diagnosis of pulmonary tuberculosis (PTB) Adult patients. LJ culture media was used as the gold
standard for sub-samples. All data was entered into an excel spreadsheet, then transfer and
analyzed using SPSS version 20. Descriptive statistics was performed and data presented in
tables. McNamara’s and Kappa statistics was used for proportion and the percent agreement
analysis.
Results: A total of 358 pulmonary tuberculosis and MDR-TB (Multi drug resistance
tuberculosis) suspected patients were enrolled from December, 2013 to April, 2014 in Addis
Ababa Health research and Laboratory with mainly young adults of median age 30.5. After
excluding 8 samples that were invalid by Xpert MTB/RIF assay 350 samples were analyzed
statistically and The percent agreement between Light Emitted Diode Fluorescent microscopy
and Ziehl-Neelsen smear microscopy, Xpert MTB/RIF assay and Light Emitted Diode
Fluorescent microscopy, Xpert MTB/RIF assay and Ziehl-Neelsen smear microscopy for MTB
detection showed that k=75%(95%CI,67% to 81%), p<.0005, k=81.8%(95%CI, 81% to 82.6%)
p<.0005 and k=72.6%(95%CI,61.6%to82.6%), p<.0005, respectively. The percent agreement of
the three tests showed that there were an overall percent agreement of 87.4%, 84.6%, and 90.9%
between Light Emitted Diode Fluorescent microscopy and Ziehl-Neelsen microscopy, Xpert
MTB/RIF assay and Ziehl-Neelsen microscopy, and Light Emitted Diode Fluorescent
microscopy and Xpert MTB/RIF assay respectively. In the sub group study the sensitivity,
specificity, PPV and NPV achieved with direct Ziehl-Neelsen microscopy, Light Emitted Diode
Fluorescent microscopy and Xpert MTB/RIF using culture as a gold standard in 167(47%)
samples were (76.9%, 96%, 97.8% and 64%), (81.2%, 90%, 95%, 67.2%) and (89.7%, 92%,
96.3%, 86.2%) respectively.
Conclusion: Xpert MTB/RIF assay has better yield than Light Emitted Diode Fluorescent smear
microscopy and Ziehl-Neelsen smear microscopy with incremental yield of 12.8% and Light
Emitted Diode Fluorescent smear microscopy has better yield than Ziehl-Neelsen smear
microscopy with incremental yield of 4.8% therefore Xpert MTB/RIF assay is a highly accurate
diagnostic tool for MTB detection, which achieves a substantial reduction in diagnostic delay
With overall performance characteristics that are superior to Light Emitted Diode Fluorescent
smear microscopy and Ziehl-Neelsen smear microscopy.
Keywords: Light Emitting Diode Fluorescent Microscopy (LED-FM), Ziehl-Neelsen (ZN),
Xpert MTB/RIF assay
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Keywords
Light Emitting Diode Fluorescent Microscopy (LED-FM), Ziehl-Neelsen (ZN), Xpert MTB/RIF assay