Workup of gastrointestinal microsporidiosis.

Microsporidia, which are members of the phylum Microspora, are increasingly recognized as causing opportunistic infections in persons with immunodeficiency (e.g., AIDS). Diarrhea is the predominant clinical sign associated with infections by two Microsporidia, namely Enterocytozoon bieneusi and Encephalitozoon intestinalis (which was formerly named Septata intestinalis). Prevalence rates of microsporidiosis in persons with AIDS and chronic diarrhea range fron 7 to 50%. Transmission electron microscopy has been the gold standard by which to diagnose microsporidiosis and requires observing a polar filament which is the structure distinguishing Microsporidia from other organisms. Transmission electron microscopy is difficult, time-consuming, costly, relatively insensitive, and requires a great deal of expertise. As such, histochemical methods have been developed and improved for detecting Microsporidia. Diagnoses from stool specimens or enteric fluids can be made using the chitin-staining fluorochromes (e.g., Calcofluor White) and the modified trichrome stain which are highly sensitive, particularly when both are used. Immunofluorescent antibody staining methods are being developed to improve specificity, but reagents are not yet commercially available. Microsporidia can be detected most readily in tissue biopsies by Gram stain, Giemsa stain, or immunofluorescent antibody. Polymerase chain reaction methods are in their infancy for application, but should prove to be particularly sensitive and specific in the future.