Blastocystis Infection

1 What is Blastocystis Hominis Infection?

Blastocystis hominis is a common microorganism that thrives in the intestine, and is found in the stools of healthy people without any problems in the digestive system. Sometimes, Blastocystis hominis is isolated from the stools of people with diarrhea, abdominal pain, and other gastrointestinal disorders. The role that Blastocystis hominis plays in causing an infection is not completely understood by researchers. An infection caused by Blastocystis hominis is called blastocystosis.

Certain forms of Blastocystis hominis are more likely to be linked to an infection causing symptoms. Sometimes, the microorganism simply lives in a person's digestive tract without being harmful. Blastocystosis usually clears up on its own.

There are no definitive and proven treatments for these infections. However, if your symptoms do not improve, your doctor may advise certain medications.

2 Symptoms

Signs and symptoms that may occur in association with blastocystis hominis infection include:

  • Diarrhea: Watery, loose stools
  • Nausea
  • Abdominal pain felt like cramps
  • Bloating
  • Excessive gas (flatulence)
  • Hives
  • Loss of appetite
  • Weight loss 
  • Itching sensation around the anal region
  • 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.

3 Causes

The exact cause of blastocystis hominis infection is unknown.

Earlier classified as a harmless yeast, blastocystis is now explained as a parasite, which is a microscopic single-celled organism (protozoan). Several protozoans that are normal inhabitants of your gastrointestinal tract are harmless or even helpful sometimes, but others may cause disease.

However, whether blastocystis is the type of protozoa that causes disease is still controversial. As many people who carry blastocystis have no signs or symptoms, and the microorganism is also found in people with diarrhea and other digestive problems, the etiology of the infection is unclear. Blastocystis commonly appears with other organisms, therefore, it is not clear whether it is a causative organism or an innocent bystander.

At the same time, it may also be possible that some people act as carriers of blastocystis. These carriers do not show any signs or symptoms of infection. The incidence of symptoms does not increase with higher number of parasites.

Although, it is not known for sure how blastocystis gets transmitted into the digestive system, experts suspect that blastocystis may get into the intestinal tract through oral-fecal contact. This occurs when a person does not wash his or her hands thoroughly after using the toilet and before preparing food. The prevalence of blastocystis hominis infection is high in areas with inadequate sanitation and poor personal hygiene.

4 Making A Diagnosis

Making diagnosis of blastocystis hominis infection is done by several tests.

You may probably consult your primary care doctor at first. However, sometimes, when you call to schedule an appointment, you may be referred directly to an infectious disease specialist or someone who specializes in digestive system disorders (gastroenterologist).

It is always better to be prepared for your appointment as these could be brief. Here is some information that can help you in getting ready for your appointment, and know what to expect from your doctor.

What you can do

    Be aware of your pre-appointment restrictions. To know this, make sure you ask while you make an appointment, whether you need to do anything in advance, such as restrict your diet. Write down the following information:

  • All the symptoms you are experiencing, including those that seem unrelated to the reason for your appointment.
  • Key personal information, including major stresses or recent life changes. 
  • Let your doctor know if you have recently been on a travel out of the country, especially to a developing country.
  • All regular medications, vitamins or supplements you take.

Write down questions to ask your doctor

  Preparing a list of questions you need to ask your doctor will save a lot of time. Some basic questions to ask your doctor include:

  • What is the most likely cause of my symptoms?
  • Are there any other possible causes?
  • Do I need some tests?
  • What treatments are available, and which one do you suggest?
  • Is there any generic alternative to the medicine you have prescribed?
  • Are there brochures or other printed materials that can be referred ? What websites do you recommend?

In addition to the above questions, do not hesitate to ask any questions that may arise during your appointment.

What to expect from your doctor

  Your doctor may ask you a number of questions to which you may keep your answers ready. Your doctor may ask:

  • When did you start experiencing symptoms?
  • Are your symptoms continuous or do they come and go?
  • Are your symptoms very severe?
  • Is there anything that seems to improve or worsen your symptoms?
  • Did you visit any other country recently?
  • Are you having any other health problems?

What you can do in the meantime

If your symptoms are because of blastocystis, these usually resolve on their own even before you see your doctor. Make sure that you stay well-hydrated in the meantime. Oral rehydration solutions are available at all drugstores and health agencies worldwide. These effectively replace the lost fluids and electrolytes.

Otherwise, you can make your own oral rehydration solution by mixing 5 cups (about 1 liter) of bottled or boiled water with 6 level teaspoons (about 34 grams) of table sugar and 1/2 level teaspoon (about 3 grams) of table salt.

You should not take anti-diarrheal medications because these can worsen some diarrheal illnesses.

It is very difficult to diagnose the cause of your diarrhea. Sometimes, even if blastocystis hominis is seen on a fecal exam, it may not be the cause for your symptoms.

Your doctor will take your medical history, ask about your recent activities, such as traveling, and perform a careful physical examination. Few lab tests may be ordered, which help in the diagnosis of parasitic diseases and other noninfectious causes of gastrointestinal symptoms:

  • Stool (fecal) examination: This test checks for the presence of parasites or their eggs (ova) in the stool sample. To collect your stool sample, your doctor will give you a special container with a preservative fluid. Refrigerate, but do not freeze these samples until you take it to your doctor's office or laboratory.
  • Endoscopy: Your doctor may need to perform this test if fecal examination does not reveal the cause, and you continue to have symptoms. After sedation, your gastroenterologist will pass a flexible tube into your mouth or rectum to visualize your gastrointestinal tract and find out the cause of your symptoms. You will need to start fasting at least about 6-8 hours before the test.
  • Blood tests: A blood test for detection of blastocystis is currently available, but is not used commonly. However, your doctor may order blood tests to rule out other causes of your signs and symptoms.

5 Treatment

Mild signs and symptoms of blastocystis hominis infection get better on their own without any treatment. If there are no signs or symptoms, then you do not require treatment. 

Potential medications helpful in treating blastocystis hominis infection include:

However, the response to medication for blastocystis infection varies greatly among individuals. If the symptoms you have are unrelated to blastocystis, it may be possible that medication's effect on another organism will result in an improvement of your symptoms.

6 Prevention

You can prevent blastocystis hominis infection or other gastrointestinal infection by taking certain precautionary measures while traveling in high-risk countries.

    Watch what you eat

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

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

  Don't drink the water

    When traveling to high-risk countries, where the water supply may be unsafe, keep the following things in mind:

  • Avoid drinking unboiled water — from tap, well or stream. If you need to drink local water, boil it for at least three minutes, and then let it cool to room temperature.
  • Avoid ice cubes or fruit juices prepared using tap water.
  • It is safe to drink canned or bottled drinks in their original containers — including water, carbonated beverages, pasteurized fruit drinks, beer or wine — as long as you break the seals on the containers yourself. Wipe off any can or bottle before drinking or pouring.
  • Avoid consuming uncooked food washed with unboiled tap water. Beware of sliced fruit that may have been washed in contaminated water.
  • Avoid swimming in water that is contaminated.
  • Keep your mouth closed while taking a shower to avoid tap water from getting inside your body.
  • Use bottled water for brushing your teeth.
  • Use bottled or boiled water to prepare milk from baby formula.
  • Make sure hot beverages, such as coffee or tea, are steaming hot.

If it is not possible to buy bottled water or boil your water, buy some device to purify water: Look for filters that advertise the Environmental Protection Agency (EPA) designation of water purifier. Although the EPA does not independently verify these filters, the designation means that they are capable of filtering hundreds of bacteria, viruses, and parasites.

Another method is chemical disinfection of water using iodine or chlorine. Iodine, although more effective, should be reserved for short trips as excessive amounts of iodine are harmful to your body.

 Take precautions to avoid transmitting a parasite to others

   If you have blastocystis or any other gastrointestinal infection, good personal hygiene methods should be followed to avoid spreading of the infection to others:

         Wash your hands with soap and warm water frequently, especially after using the toilet, changing diapers, and before handling food. Rub soapy, wet hands against each other for at least 20 seconds before rinsing. Use an alcohol-based hand sanitizer if soap and water are unavailable.

         Wash your hands thoroughly changing a diaper even if you wear gloves, especially if you work in a child care center.

7 Risks And Complications

Risk factors

Blastocystis hominis infection is a common infectitious condition, and every person is at risk of having the organism in his or her stools. A person who travels to or resides in areas where there is improper sanitation and water is contaminated and unsafe, is at a greater risk of this infection. Studies suggest that risk of infection increases through following factors:

  • Ingestion of contaminated food or water
  • Exposure to a day care environment
  • Exposure to infected animals


Diarrhea associated with blastocystis is usually self-limiting. However, diarrhea may cause loss of vital fluids, salts and minerals, which can further lead to dehydration, especially in children.