The diagnosis of old and new gastrointestinal parasites.

For the foreseeable future, light microscopy will continue to be the method of choice for diagnosing gastrointestinal parasites. However, in selected circumstances, the use of commercially available immunofluorescent kits will supersede the use of routine light microscopy for diagnosis of Giardia lamblia and Cryptosporidium parvum. These techniques may used to diagnose invasive amebic infections caused by E. histolytica in the future. Pooling stool samples from the same or even different patients may offer a means to process specimens in a more efficient and cost-effective manner without lowering the predictive value of an ova and parasite examination. Although we suggest that, with some exceptions, stools for ova and parasite examination should not be accepted past the fourth day of hospitalization, we cannot recommend the use of a single stool sample for diagnosis without extensive studies in individual parasitology laboratories. Techniques have still not been developed for the optimum methods of concentration of stool for diagnosis of coccidian infections. For most laboratories, the diagnosis of microsporidian infections remains problematic because of the lack of a commercial source for oocysts to provide positive control material. (Note: There is now a commercial source for oocysts available.)