Blastocystis Hominis Infection

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What is blastocystis hominis?

Blastocystis hominis is a common microscopic parasite organism found throughout the world. Infection with blastocystis hominis is called blastocystosis (BLASS-toe-SIS-toe-sis).

What are the symptoms of blastocystosis?

Watery or loose stools, diarrhea, abdominal pain, anal itching, weight loss, and excess gas have all been reported in persons with blastocystosis. Many people have no symptoms at all.

How long will I be infected?

Blastocystis can remain in the intestines for weeks, months or years.

Is blastocystosis the cause of my symptoms?

It is hard to be sure and experts disagree on this point. Whether or not blastocystis is the primary cause of your symptoms is unknown. Finding it in stool samples should be followed up with a careful search for other possible causes of your symptoms. Symptoms may be caused by infection with other parasitic organisms, bacteria or viruses. Often blastocytis 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 your symptoms. Hormone or endocrine diseases, diseases like Crohn's and colitis, or hereditary factors may be the cause of illness. Food additives or food allergies may also be a cause of abdominal discomfort.

Is having blastocystosis common?

Yes. In fact, many people have blastocystosis without ever having symptoms.

What should I do if I think I have blastocystosis?

See your health care provider. He or she will ask you to provide stool samples for testing. Diagnosis may be difficult, so you may be asked to submit several stool samples.

Is medication available to treat blastocystosis?

Yes, drugs are available by prescription to treat blastocystosis; however, sometimes medication is not effective.

How did I get blastocystosis?

How blastocystosis is transmitted is unknown, although the number of people infected seems to increase in areas where sanitation and personal hygiene are inadequate.

How can I prevent infection with Blastocystis?

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

• Avoid water or food that may be contaminated.

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

• When traveling to countries where the water supply may be unsafe, avoid drinking unboiled tap water and avoid uncooked foods washed with unboiled tap water. Bottled or canned carbonated beverages, seltzers, pasteurized fruit drinks, and steaming hot coffee and tea are safe to drink.

• If you work in a childcare centre and 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.

Should I be concerned about spreading infection to the rest of my household?

No. If you practice adequate personal hygiene, including proper hand washing with soap and warm water after using the toilet and before handling food, there is little risk of spreading infection.

For more information:

1. Albrecht J, Stellbrink HJ, Koperski K, et al. Blastocystis hominis in human immunodeficiency virus-related diarrhea. Scand J Gastroenterol 1995;30:909-14.

2. Markell EK, Udkow MP. Blastocystis hominis; pathogen or fellow traveler? Am J Trop Med Hyg 1986;35:1023-6.

3. Miller RA, Minshew BH. Blastocystis hominis: an organism in search of a disease. Rev Infect Dis 1988;10:930-8.

4. Udkow MP, Markell EK. Blastocystis hominis; prevalence in asymptomatic versus symptomatic hosts. J. Infect Dis 1993; 168:242-4.

5. Zuckerman MJ, Watts MT, Ho H., et al. Blastocystis hominis infection and intestinal injury. Am J Med Sci 1994;308:96-101.

Centre for Disease Control, Department of Health & Human Services, 1998