Demonstration of Isospora belli by acid-fast stain in a patient with acquired immune deficiency syndrome.

Isospora belli, like Cryptosporidium sp., a sporozoan parasite of the small intestine, has been isolated from both immunodeficient and immunologically normal persons. In immunocompetent persons the infection may be asymptomatic; it frequently causes mild and self-limited diarrhea. The spectrum of the disease in persons with acquired immune deficiency syndrome is not well established. I. belli did not stain well with the methods usually used for intestinal protozoa and was difficult to see unstained. However, it stained well with the acid-fast technique used for Cryptosporidium sp. and was easily identified by such stains. A case of combined infection with Cryptosporidium sp. and I. belli is reported.