An overnight sedimentation method: improving the diagnosis of tuberculosis when electrical centrifuge is not available.

An experimental comparative study was conducted in order to compare the positivity pattern of sputum microscopy using the direct and overnight sedimentation Ziehl-Neelsen (ZN) smears, direct and NaOCl pretreated centrifuged ZN smears and overnight sedimentation and NaOC1 pretreated centrifuged ZN smears methods. We examined 660 sputum smeared slides for the presence of acid-fast bacillus from 220 sputum samples. Compared with the direct microscopy method, positivity increased by 91.1% after centrifugation (P < 0.001, chi(2) = 18.27) and by 71.1% after overnight sedimentation (P < 0.001, chi(2) = 11.61). No statistical significant difference was observed between the results of two different concentration techniques (P > 0.05, chi(2) = 0.789). The application of overnight sedimentation (in a laboratory without electricity) and/or the centrifugation technique could make a positive impact on the effectiveness of national tuberculosis control programmes.