People can become infected with Cystoisospora by consuming food or water contaminated with the parasite.
Cystoisosporiasis symptoms are more severe and prolonged in people with a weakened immune system, such as people with AIDS.
Symptoms vary but include watery diarrhea, abdominal cramping, fever, and weight loss.
Doctors usually diagnose the infection by identifying Cystoisospora in a sample of stool.
Cystoisosporiasis can be treated with trimethoprim /sulfamethoxazole (TMP/SMX).

(See also Overview of Parasitic Infections.)
Cystoisosporiasis is most common in tropical and subtropical climates. When encountered in the United States, it is usually in immigrants or travelers with exposure in endemic areas.