Overview

Blastocystis hominis is a microscopic organism that may be found in the stools of healthy people who aren't having any digestive symptoms. Blastocystis hominis is also sometimes found in the stools of people who have diarrhea, abdominal pain or other gastrointestinal problems.

Researchers don't yet fully understand the role that Blastocystis hominis plays, if any, in causing an infection. Certain forms of Blastocystis hominis may be more likely to be linked to an infection with symptoms. Sometimes, blastocystis simply lives in a person's digestive tract without causing harm.

A Blastocystis hominis infection usually clears up on its own. There are no proven treatments for these infections. But, if your symptoms don't get better, your doctor may recommend trying certain medications.

Symptoms

Signs and symptoms that might be associated with blastocystis include:

  • Diarrhea
  • Nausea
  • Abdominal cramps
  • Bloating
  • Excessive gas (flatulence)
  • Hives
  • Loss of appetite
  • Fatigue

When to see a doctor

See your doctor if you have signs and symptoms, such as diarrhea or cramps, that last longer than three days.

Causes

Once thought to be a harmless yeast, blastocystis is a parasite — a microscopic single-celled organism (protozoan). Many protozoans normally inhabit your gastrointestinal tract and are harmless or even helpful; others cause disease.

Whether blastocystis is the type of protozoa that causes disease is controversial. While many people who carry blastocystis have no signs or symptoms, the organism is also found in people who have diarrhea and other digestive problems. Blastocystis often appears with other organisms, so it's not clear whether it causes disease on its own or is an innocent bystander.

It's also possible that some people may be carriers of blastocystis. These carriers don't have any signs or symptoms of infection. And, the incidence of symptoms doesn't go up with an increase in the number of parasites.

Although no one knows for sure how blastocystis gets into the digestive system, experts suspect that blastocystis may get into the intestinal tract through oral-fecal contact. This can occur when a person doesn't wash his or her hands thoroughly after using the toilet before preparing food. The prevalence of blastocystis increases in places with inadequate sanitation and poor personal hygiene.

Risk factors

Blastocystis is common, and anyone can have the organism in his or her stools. You may be at higher risk if you travel or live where sanitation is inadequate or where the water may not be safe.

Complications

If you have diarrhea associated with blastocystis, it's likely to be self-limiting. However, anytime you have diarrhea, you lose vital fluids, salts and minerals, which can lead to dehydration. Children are especially vulnerable to dehydration.

Prevention

You may be able to prevent blastocystis or other gastrointestinal infection by taking a number of precautions while traveling in high-risk countries.

Watch what you eat

The general rule of thumb is this: If you can't boil it, cook it or peel it — forget it. Try to remember these more-specific tips:

  • Avoid food from street vendors.
  • Avoid unpasteurized milk and dairy products, including ice cream.
  • Avoid raw or undercooked meat, fish and shellfish.
  • Steer clear of moist food at room temperature, such as sauces and buffet offerings.
  • Eat foods that are well-cooked and served hot.
  • Stick to fruits and vegetables that you can peel yourself, such as bananas, oranges and avocados. Stay away from salads and unpeelable fruits, such as grapes and berries.
  • Avoid frozen pops and flavored ice.
  • Skip salsa and other condiments made with fresh ingredients.

Don't drink the water

When visiting high-risk countries, keep the following tips in mind:

  • Avoid unsterilized water — from tap, well or stream. If you need to consume local water, boil it for at least three minutes and then let it cool to room temperature.
  • Avoid ice cubes or fruit juices made with tap water.
  • Beware of sliced fruit that may have been washed in contaminated water.
  • Don't swim in water that may be contaminated.
  • Keep your mouth closed while showering.
  • Feel free to drink canned or bottled drinks in their original containers — including water, carbonated beverages, beer or wine — as long as you break the seals on the containers yourself. Wipe off any can or bottle before drinking or pouring.
  • Use bottled water to brush your teeth.
  • Use bottled or boiled water to mix baby formula.
  • Make sure hot beverages, such as coffee or tea, are steaming hot.

If it's not possible to buy bottled water or boil your water, bring some means to purify water: Look for filters that advertise the Environmental Protection Agency (EPA) designation of water purifier. Although the EPA doesn't independently verify these filters, the designation means they are supposed to filter hundreds of bacteria, viruses and parasites.

Another approach is to chemically disinfect water with iodine or chlorine. Iodine tends to be more effective, but reserve it for short trips, because too much iodine can be harmful to your body.

Take precautions against passing a parasite to others

If you have blastocystis or another gastrointestinal infection, good personal hygiene can help keep you from spreading the infection to others:

  • Wash hands with soap and water frequently, especially after using the toilet and before handling food. Rub soapy, wet hands together for at least 20 seconds before rinsing. If soap and water aren't available, use an alcohol-based hand sanitizer.
  • Wash hands well after changing a diaper, especially if you work in a child care center, even if you wear gloves.