Authors: Merid, Y.¹; Yassin, M.A.²; Yamuah, L.³; Kumar, R.⁴; Engers, H.³; Aseffa, A.³

Source: The International Journal of Tuberculosis and Lung Disease, Volume 13, Number 1, January 2009 , pp. 136-141(6)

Publisher: International Union Against Tuberculosis and Lung Disease

Abstract:

SETTING: Health centres in Awassa, southern Ethiopia.

DESIGN: Consecutive patients visiting health centre laboratories for the evaluation of suspected pulmonary tuberculosis (TB) between June and September 2006 were investigated. On-the-spot, morning and second on-the-spot sputum samples were pooled for each patient. Direct smears were stained with hot Ziehl-Neelsen (ZN) technique and aliquots cultured for mycobacteria on Löwenstein-Jensen media. The remaining sputum was treated with household bleach, aliquoted and processed with short-term digestion, centrifugation and sedimentation techniques, and stained with ZN.

RESULTS: Acid-fast bacilli were detected in respectively 126 (25%), 141 (28%), 169 (34%) and 198 (40%) of the 497 pooled sputum samples processed by the direct, short-term, sedimentation and centrifugation techniques (P < 0.001). The sensitivity of the direct, short-term, sedimentation and centrifugation techniques was respectively 51.1%, 53.2%, 57.6% and 63.6%. The difference between the direct smear and centrifugation (P < 0.001) or sedimentation (P < 0.005) methods was significant. The specificity of the direct, short-term digestion, sedimentation and centrifugation techniques was respectively 97%, 93%, 86.5% and 80.8%.

CONCLUSIONS: Bleach treatment of sputum and centrifugation significantly improves the sensitivity of smear microscopy for the diagnosis of TB in a health centre in a high TB burden area. It is more sensitive, but possibly less specific, than other bleach methods.

Keywords: acid-fast bacilli; microscopy; bleach; pooled sputum validation

Document Type: Regular paper

Affiliations: 1: Armauer Hansen Research Institute, Addis Ababa, Ethiopia; Department of Microbiology, Immunology and Parasitology, Addis Ababa University Medical Faculty, Addis Ababa, Ethiopia; Southern Region Health Bureau, Awassa, Ethiopia 2: Liverpool School of Tropical Medicine, Liverpool, UK 3: Armauer Hansen Research Institute, Addis Ababa, Ethiopia 4: Department of Microbiology, Immunology and Parasitology, Addis Ababa University Medical Faculty, Addis Ababa, Ethiopia

Publication date: 2009-01-01

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