Enterocytozoon bieneusi infection in an immunocompetent patient who had acute diarrhea and who was not infected with the human immunodeficiency virus.

Enterocytozoon bieneusi is a microsporidian species that has been detected exclusively in patients infected with human immunodeficiency virus (HIV) who are severely immunocompromised. We report what we believe is the first case of E. bieneusi infection in an HIV-negative patient with acute, self-limited diarrhea whose CD4+ cell count was not depressed.