Evaluation of Kato Thick-Smear Technique for Quantitative Diagnosis of Helminth Infections

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Abstract
Summary A method of fecal examination described by Kato and involving the clearing of a direct fecal smear pressed thin under a glycerin-impregnated cellophane coverslip was evaluated for possible use in quantitative diagnosis of helminth infections. Modifications were described for 1) removing fiber from the fecal sample, 2) uniformly spreading the smear, and 3) preventing over-clearing of the preparation. Optimum time for clearing the smears was found to be about 30 minutes at 35°C, or about 1 hour under openroom conditions. The thick-smear method was found to be as sensitive as the Bell filtration, zine-surface flotation, and Hoffman sedimentation methods of concentration of feces. Egg-counts for estimation of intestinal nematode and Schistosoma mansoni infections were as reproducible when made by the thick-smear method as by dilution or concentration procedures. Series of egg-counts made from the same stool and from daily stools indicated that eggs of S. mansoni, as well as those of other worms, are distributed randomly in the feces and are in equal numbers in the outer and inner portions of the stool. Thus egg-counts made by the thick-smear technique appear to be reliable for the quantitative diagnosis of helminth infect ons.