Fluorescence microscopy for the diagnosis of smear-negative pulmonary tuberculosis in Ethiopia

• Main Authors: Gemeda Abebe (Author), Dossegnaw Aragaw (Author), Mulualem Tadesse (Author)
• Format: Book
• Published: AOSIS, 2020-09-01T00:00:00Z.
• Subjects: article
• Online Access: Connect to this object online.
• Notes: 2225-2002; 2225-2010; 10.4102/ajlm.v9i1.810
• Keywords: sputum smear-negative; light-emitting diode fluorescent microscopy; bleach pretreatment; ethiopia; health; Public aspects of medicine; RA1-1270; Medicine (General); R5-920
• Source: African Journal of Laboratory Medicine, Vol 9, Iss 1, Pp e1-e6 (2020)

Background: Despite its low sensitivity, microscopy remains the main method for the diagnosis of pulmonary tuberculosis in most laboratories in Ethiopia. Few studies have evaluated the performance of light-emitting diode fluorescent microscopy (LED-FM) in bleach-concentrated smear-negative sputum specimens. Objective: This study aimed to evaluate the diagnostic performance of LED-FM for smear-negative pulmonary tuberculosis in Ethiopia. Methods: A total of 194 adult patients with a cough lasting for more than two weeks, and who had three direct smear-negative sputum tests for Mycobacterium tuberculosis by Ziehl-Neelsen light microscopy, were included. All direct Ziehl-Neelsen-stained smear-negative sputum samples were cultured and were also visualised by LED-FM. Smears for LED-FM were performed from bleach-concentrated sputum sediment. The diagnostic performance of the LED-FM was compared to the culture method (the reference standard). Results: Of the 194 smear-negative sputum specimens analysed, 28 (14.4%) were culture-positive and 21 (10.8%) were LED-FM-positive for M. tuberculosis. However, only 11 of the 21 (52.4%) LED-FM-positive patients had a confirmed tuberculosis diagnosis by culture. Light-emitting diode fluorescence microscopy (FM) had a sensitivity of 39.3% (95% confidence interval: 21.2-57.4) and specificity of 93.9% (95% confidence interval: 90.4-97.6). Ten LED-FM-positive specimens were culture-negative, and all of these specimens had scanty grading (1-19 bacilli per 40 fields on LED-FM). Conclusion: This study showed that implementation of LED-FM on bleach pre-treated and concentrated sputum can significantly improve the diagnosis of smear-negative pulmonary tuberculosis. However, all scanty grade, positive smears by LED-FM need to be confirmed by reference culture method.