Evaluation of bleach-sedimentation for sterilising and concentrating Mycobacterium tuberculosis in sputum specimens

Table 1 Comparison of conventional smears and smears prepared from bleach-sedimented sputum

	Conventional smears	Smears prepared from bleach-sedimented sputum *	p-value
Acid-fast bacilli counts per 100 microscopy fields, geometric mean (95% CI)	346 (139-862)	166 (68-406)	0.02
Slide-reading time, arithmetic mean minutes (standard error of the mean)	11.2 (0.92)	9.6 (0.69)	0.03
Inter-observer agreement, correlation coefficient (r)	0.991	0.997	-
Correlation between concentrating effect of bleach-sedimentation and acid-fast bacilli counts, correlation coefficient (r)	-0.46		0.02
Correlation between concentrating effect of bleach-sedimentation and volume of the sputum specimen, correlation coefficient (r)	-0.13		0.7
Concentrating effect of bleach-sedimentation comparing salivary versus mucoid sputum specimens	-		0.3
Concentrating effect of bleach-sedimentation comparing moderately versus very experienced microscopists	-		0.6

* False-negative (zero) microscopy readings by a single microscopist for 3 strongly positive smears prepared from bleach-sedimented specimens were excluded when calculating these data (see text and Figure 5).

ISSN: 1471-2334