A sedimentation-selective filtration method for the diagnosis of light infections with Schistosoma mansoni

An epidemiological survey for infection with Schistosoma mansoni was carried out in the community of Catharina Sophia in northern Surinam. The merits of a more sensitive diagnostic system, the Sedimentation-Selective-Sieving (SSF) method, were evaluated; the results were compared with those obtained with the standard Kato-Katz thick smear technique. Examination of a duplicate Kato smear (2 x 25 mg) resulted in a prevalence of 22% while the real prevalence was shown to be more than 42%. The SSF procedure was shown to have a comparatively high sensitivity although the egg counts per gram (calculated on the basis of examining samples of 2-3 g) were considerably lower than those derived from Kato smears. The implications for epidemiological surveillance of communities with excretion of low numbers of S. mansoni eggs are discussed and the observations are compared with those one might expect on the basis of mathematical modelling (De Vlas et al., 1992).