Evaluation of the Kato-Katz Thick Smear and Formal Ether Sedimentation Techniques for Quantitative Diagnosis of Schistosoma mansoni Infection

A. EbrahimDepartment of Tropical Health, High Institute of Public Health, Alexandria University, Alexandria, Egypt

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H. El-MorshedyDepartment of Tropical Health, High Institute of Public Health, Alexandria University, Alexandria, Egypt

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E. OmerDepartment of Tropical Health, High Institute of Public Health, Alexandria University, Alexandria, Egypt

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S. El-DalyDepartment of Tropical Health, High Institute of Public Health, Alexandria University, Alexandria, Egypt

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R. BarakatDepartment of Tropical Health, High Institute of Public Health, Alexandria University, Alexandria, Egypt

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The present study compared the Kato-Katz thick smear and formol ether sedimentation techniques in the diagnosis of Schistosoma mansoni infections. A stool specimen was collected from 915 individuals representing a high prevalence community (63.3%) and from 471 individuals representing a relatively low prevalence village (40%). The overall sensitivity of a single Kato-Katz smear was 70.8%, and it increased with each additional slide to reach 91.7% on examining four smears. However, the sensitivity was 83.3% when using the formol ether sedimentation technique. In terms of quantitative analysis, the geometric mean egg count was 94 eggs per gram (epg) of stool by two Kato-Katz smears, and 43 epg by the sedimentation technique. This means that more than 50% of eggs were missed when using the sedimentation technique, a fact that should be taken into consideration when relating infection level with morbidity.

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