Blastocystis hominis is a microscopic parasite sometimes found in the stools of healthy people as well as in the stools of those who have diarrhea, abdominal pain or other gastrointestinal problems. Infection with blastocystis is called blastocystosis.
Researchers don't yet fully understand the role that blastocystis plays, if any, in causing an infection. Certain subtypes of blastocystis may be more likely to cause symptomatic infection, or may pose a risk only when combined with other types of infection. In some cases, blastocystis simply resides in the digestive tract without causing harm.
There are no proven treatments for blastocystosis, and the infection usually clears up on its own. However, if signs and symptoms don't improve, your doctor may recommend trying medications.