CONCENTRATION: Procedure Limitations (cont.)

permanent stained smear. In clinically important infections, the number of helminth eggs present would ensure detection regardless of the type of preservative used. Also, the morphology of S. stercoralis larvae is not as clear from PVA as from specimens fixed in formalin.

4. For unknown reasons, I. belli oocysts are routinely missed in the concentrate sediment when concentrated from PVA-preserved specimens. The oocysts would be found if the same specimen was preserved in formalin rather than PVA.

5. In past publications, recommended centrifugation times have not taken into account potential problems with the recovery of Cryptosporidium oocysts. There is anecdotal evidence and personal experience (Lynne Garcia) to strongly indicate that Cryptosporidium oocysts may be missed unless the centrifugation speed is 500 x g for