oa South African Medical Journal - Routine stool examinations : confirmation of the value of the acid-sulphate ether concentration test
Our experience with the various methods used in the examination of stools shows that cases of intestinal bilharzias (Bilharzia mansoni) are likely to be missed by the usual methods of stool examination but are less likely to be missed by the acid-sulphate ether concentration method. Many more cases of Ankylostoma infestation, and a considerable number of infestations with Taenia spp., Ascaris lumbricoides and Trichuris trichiura areby this method. In no instance where T. Trichiura or Ankylostoma ova were found did the concentration test fail to confirm the direct finding, while many additional cases were found. Sixteen cases of Bilharzia masoni infestation were found by the acid-sulphate ether method and of these cases, one only would have been found by the usual direct examination. In the stools positive by concentration only, the findings of ova varied from 1-9. In one case, the direct examination showed 3 ova of B. mansoni and one hookworm ovum. On concentration, the same specimen yielded 166 hookworm ova and 53 B. Mansoni ova, and a subsequent concentration of a repeat stool showed 76 Bilharzia ova as compared with 3 on direct examination. In only one instance had there been a specific request to look for intestinal bilharzia. The ovum with the most variable results was A. lumbricoides. The fertilized ovum often disintegrates partially, making recognition difficult. Untertilized ova are better able to withstand processing. In spite of this, innumerable cases of Ascaris, missed in the direct examinations, were found in the concentrations. The series of specimens examined is rather limited to express any opinion on O. vermicularis, but we do not expect to find many by concentration as these ova are not often found on direct examination, owing to their normal site of deposition on the peri-anal skin. We consider that in spite of the extra time and material required, the acid-sulphate ether method can be recommended as a routine test to demonstrate ova, particularly in areas where intestinal bilharziasis and hookworm are prevalent.
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