Improved detection of Acid-fast bacilli in sputum by the bleach-concentration technique at Gondar University teaching hospital, Northwest Ethiopia

Background: Direct sputum smear microscopy remains the most widespread method for the diagnosis and followup of patients with tuberculosis despite its limited sensitivity. Objective: Our aim was to investigate whether sputum smears prepared using liquefaction with household bleach and concentration by centrifugation was more sensitive for the detection and quantification of acid-fast bacilli as compared to smears processed directly from sputum. Methods: A cross-sectional study was conducted among patients with a clinical presentation suggestive of pulmonary tuberculosis at Gondar University Hospital, Northwest Ethiopia in April 2008. Three consecutive sputum samples were collected from the study participants and examined for acid fast bacilli using the standard direct microscopy as well as the household bleach-concentration technique. Results: Out of 264 samples examined, 33(12.5%) were smear positive by direct microscopy and 61 samples (23.2%) were smear positive by the bleach-concentration method (OR 2.1, 95% Cl 1.3-3.4, p<0.01). There was an absolute increase in the number of acid fast bacilli per slide using the bleach-concentration technique compared to the direct method. The detection of acid fast bacilli was superior in early morning sputum followed by overnight spot samples. Conclusion: The bleach-concentration method for sputum smear samples significantly increased the detection rate of smear positive patients compared to the direct method. Thus, a shift from direct sputum microscopy to the bleach-concentration technique should be considered. Acid fast bacilli, Concentration method, Direct microscopy, Ethiopia, Tuberculosis.