Effect of bleach-sedimentation on the concentration of acid-fast bacilli. The number of acid-fast bacilli visualised by smear-microscopy is shown. Each of the open circles represents the geometric mean number of acid-fast bacilli visible in 100 microscopy fields for triplicate, identically prepared slides. Each line joins the data derived from 1 of the 25 sputum specimens i.e. the geometric mean of triplicate conventional smear-microscopy slides (the left-hand end of each line) versus the geometric mean of triplicate slides prepared after bleach-sedimentation (the right-hand end of each line). The filled diamonds represent the geometric mean of all 25 specimens and the error bars represent 95% confidence intervals. The box parallel with the vertical axis indicates the smear-microscopy grade equivalent to the acid-fast bacilli counts per 100 microscopy fields (0 indicates none visible/100 fields; +/- indicates 1-9/100 fields; + indicates 10-99/100 fields; ++ indicates 100-999/100 fields; and +++ indicates > 1, 000/100 fields).