Blastocystis Hominis Infection

Blastocystis hominis is a common parasitic organism that can only be seen with a microscope (microscopic). It is found throughout the world. An infection with Blastocystis hominis is called blastocystosis. It lives in your colon (large intestine). It can remain there for weeks, months or years. Experts are not certain whether or not blastocystis causes disease, or even if it needs to be treated.


No one knows how people get blastocystis in their body. The number of people infected seems to increase in areas where sanitation and personal cleanliness is poor. Travelers returning from developing countries seem to be at higher risk for having blastocystis.

Careful hygiene is important to try to prevent this infection:

  • Wash hands with soap and water after using the toilet and before handling food.

  • If you work in a child care center where you change diapers, be sure to wash your hands thoroughly with plenty of soap and warm water after every diaper change, even if you wear gloves.

  • Avoid water or food that may be contaminated.

  • Wash and peel all raw vegetables and fruits before eating.

  • When traveling in countries where the water supply may be unsafe:

  • Avoid drinking unboiled tap water, drinking any drink with ice cubes and eating uncooked foods washed with unboiled tap water.

  • Bottled or canned carbonated beverages, seltzers and pasteurized fruit drinks are safe to drink.


Some experts believe bastocystis can cause these symptoms; others disagree:

  • Frequent watery or loose stools (diarrhea).

  • Abdominal pain.

  • Anal itching.

  • Weight loss.

  • Excess gas.

  • Many people have no symptoms at all.


If you or your child has the symptoms above, you will likely be asked to submit specimens of your or your child's poop (stool) for testing. If blastocystis is found in the stool, the technicians will also do a careful search for other possible causes of the symptoms.

  • Symptoms may be caused by infection with other parasitic organisms, bacteria, or viruses. Often, B. hominis is found along with other organisms that are more likely to be the cause of your symptoms.

  • Sometimes symptoms are not caused by an infection at all.

  • Antibiotics, some cancer drugs, and medications used to control high blood pressure may be causing the symptoms.

  • Hormone or endocrine diseases; diseases like Crohn's, colitis, or hereditary factors may be the cause of illness.

  • Food additives or food allergies may also cause abdominal discomfort.


Since experts cannot be sure if blastocystis is causing the symptoms, it is not clear that treatment would be helpful (it might even be harmful). Some people get better with no treatment. If no other cause is found for the symptoms, then your caregiver may suggest treatment aimed at blastocystis to see if you or your child feels better. Several medications are available by prescription to treat blastocystosis. You or your child may need follow-up testing after treatment.


  • Take any medications exactly as directed, for as long as directed.

  • Practice good personal cleanliness, including thorough hand washing with soap and warm water.

  • If you or your child is having diarrhea, be sure to drink enough fluids to avoid dehydration.


  • You or your child is not getting better even after following all your caregiver's directions, or if you get worse.

  • You or your child develops side effects to your medications.

  • You or your child is losing weight without dieting.

  • You or your child develops other abdominal problems: you or your child may need a reevaluation to see if something besides blastocystis is causing the symptoms.

  • You or your child has an oral temperature above 102° F (38.9° C).

  • Your baby is older than 3 months with a rectal temperature of 100.5° F (38.1° C) or higher for more than 1 day.


  • You or your child has severe abdominal pain.

  • You or your child has diarrhea that is not stopping.

  • You or your child has an oral temperature above 102° F (38.9° C), not controlled by medicine.

  • Your baby is older than 3 months with a rectal temperature of 102° F (38.9° C) or higher.

  • Your baby is 3 months old or younger with a rectal temperature of 100.4° F (38° C) or higher.