A Comparison of fecal examination procedures in the diagnosis of schistosomiasis mansoni

Abstract

1. 1. Fifty human stool specimens proceeding from known positive cases of S. mansoni infection were examined for eggs of this parasite by the following methods: direct saline smear, HCl-Ether centrifugation, Na 2SO 4-Triton-Ether centrifugation, SAEX centrifugation, and sedimentation by gravity in glycerinated water. 2. 2. The number of eggs available per milliliter of feces used as a basis of comparison of the efficiency of the methods being tested was determined for each sample by the Oliver-González and Hernández-Morales modification of the Stoll dilution egg counting technique. 3. 3. Some side trials were also performed with the following modifications of two of the methods under comparison: half-strength Na 2SO 4-Triton-Ether, Formol-Na 2SO 4-Triton-Ether, HCl-Na 2SO 4-Triton-Ether, and SAEX applied to 1 ml of stool. 4. 4. The percentage of specimens correctly diagnosed by the methods and modifications tested, was as follows: Direct saline smear, 84; HCl-Ether centrifugation, 96; Na 2SO 4-Triton-Ether, 98; SAEX, 92; Glycerinated water sedimentation, 100; Half-strength Na 2SO 4-Triton-Ether, 100 (six specimens only); Formol-Na 2SO 4-Triton-Ether, 100 (18 specimens only); HCl-Na 2SO 4-Triton-Ether, 100 (27 specimens only); SAEX applied to 1 ml of stool, 98. 5. 5. The average percentage of egg recovery was as follows: Direct saline smear, not determined; HCl-Ether centrifugation, 16; Na 2SO 4-Triton-Ether, 39; SAEX, 2.4; Glycerinated water sedimentation (per 5 ml of stool) 70; Half-strength Na 2SO 4-Triton-Ether, 42 (six specimens only); Formol-Na 2SO 4-Triton-Ether, 24 (18 specimens only); HCl-Na 2SO 4-Triton-Ether, 25 (27 specimens only); SAEX applied to 1 ml of stool, 20. 6. 6. It appears from the data, that on the basis of positive diagnoses none of the methods and modifications tested proved significantly better. On the basis of egg recovery, however, Na 2SO 4-Triton-Ether centrifugation, unmodified, and sedimentation by gravity in glycerinated water, did prove superior. Further and more extensive studies on the evaluation of these methods on random samples are now in progress. 7. 7. Examination by the direct saline smear (three, thick, 22 mm 2 preparations from a well stirred sample) proved highly efficient for quick verification of the existence of infection.