Abstract:
We investigated both the extent of the variation in weight of stool samples prepared by the
Kato–Katz method and its influence on egg counts and commonly used group parameters of
infection derived from them. In a first study group of 795 people, the total mean weight of
stool aliquots, prepared with templates designed to contain 28.3 mm3, was 23.0 mg with
95% of the individual values lying between 12.0 and 34.0 mg. Minimum and maximum
values were 2.4 and 49.5 mg, respectively. Frequency distributions of the individual weights,
in series of slides prepared by different laboratory assistants, showed significant differences.
In a second study group of 199 people, duplicate series of slides were prepared and
variations in the weight of examined stool were related to variations in egg count. The
correlation between repeated individual sample weights in this series was poor, but the
correlation between egg counts was good. This was translated, at aggregate level, in very
similar classifications in egg count categories. This classification was also hardly influenced
by the choice of the conversion factor to transform egg counts per slide into eggs per gram.
At the individual level, the variability in egg counts far outweighed the variability in sample
weight and was not clearly related to it. We therefore concluded that variations in weight of
examined stool are considerable, but account for only a minimal part of the important egg
count fluctuations generally observed.
