Implications of Intra- And Inter-Specimen Fecal Egg Count Variations in Diagnosing Schistosoma Mansoni Infection by the Kato-Katz Method, in Workie Mado Village, Kemise, North-East Ethiopia
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Date
2011-06
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Addis Ababa University
Abstract
Examination of stool specimens by the Kato–Katz (K–K) technique has been a standard
method for field diagnosis of intestinal Schistosomiasis. However, it has been debated
that this technique has low diagnostic sensitivity due to intra- and inter-specimen fecal
egg count variation. The relative contribution of these two sources of variation among
107 community members of Workie Mado village, northeast Ethiopia, which is known
for its high endemicity of S. mansoni infection was quantified. The diagnostic yield of
examining one, three, or five Kato–Katz thick smears prepared from one stool specimen,
using 41.7 mg templates was compared. In a subset of 11 volunteers, who had no
demonstrable eggs in their first five K–K thick smears, the advantage of examining two
additional triplet K–K thick smears from stool specimens, taken in two subsequent days
was assessed. The overall prevalence estimates of infections increased with increasing
number of slides examined. Prevalence of S. mansoni infection based on single, triplet,
and quintet K–K thick smears was 62.6%, 75.7% and 84.1%, respectively. Cumulative
prevalence obtained with two additional triplet Kato–Katz thick smears from 2nd and 3rd
day stool specimens was 85.0% and 86.0%, which is not significantly different from
quintet measurement. Compared to quintet K–K thick smears, single K–K thick smear
missed 46.8%, 2.6% and 0% of subjects with light, moderate and heavy infections,
respectively, while triplet K-K thick smears missed 19.1% of light infections and 0% of
moderate and heavy infections. We conclude that diagnostic sensitivity in such high
transmission areas can be maximized by using quintet K-K thick smears from one stool
specimen to reduce the number of missing lightly infected individuals, and thereby
examining smear-negative individuals with additional triplet K-K thick smears, from
subsequent day stool specimens. Moreover, examining only one stool specimen with
quintet K-K thick smears can also make reasonable estimates of S. mansoni infection
intensity, and it would be more feasible and less expensive approach than day-to-day
examination of individuals in communities.
Key words: Schistosoma mansoni, Kato-Katz technique, egg count, intra-specimen,
inter-specimen, Workie Mado village, Ethiopia.
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Keywords
Schistosoma mansoni, Kato-Katz technique, egg count, intra-specimen, inter-specimen, Workie Mado village Ethiopia.