Blastocystis hominis infection
Medically reviewed on January 3, 2018
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.
Signs and symptoms that might be associated with blastocystis include:
- Abdominal cramps
- Excessive gas (flatulence)
- Loss of appetite
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.
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.
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.
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.
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.
The cause of your diarrhea may be difficult to diagnose. Even if blastocystis is present on a fecal exam, it may not be causing your symptoms.
Your doctor likely will take your medical history, ask you about recent activities, such as traveling, and perform a physical exam. A number of lab tests help diagnose parasitic diseases and other noninfectious causes of gastrointestinal symptoms:
- Stool (fecal) exam. This test looks for parasites or their eggs (ova). Your doctor may give you a special container with preservative fluid for your stool samples. Refrigerate — don't freeze — your samples until you take them to your doctor's office or lab.
- Endoscopy. If you have symptoms, but the fecal exam doesn't reveal the cause, your doctor may request this test. After you're sedated, a doctor, usually a gastroenterologist, inserts a tube into your mouth or rectum to look for the cause of your symptoms. You'll need to fast beginning the night before the test.
- Blood tests. A blood test that can detect blastocystis is now available, but it isn't commonly used. However, your doctor may order blood tests to look for other causes of your signs and symptoms.
If you have blastocystis without signs or symptoms, then you don't need treatment. Mild signs and symptoms may improve on their own within a few days.
Potential medications for treating blastocystis infection include:
- Antibiotics, such as metronidazole (Flagyl) or tinidazole (Tindamax)
- Combination medications, such as sulfamethoxazole and trimethoprim (Bactrim, Septra, others)
- Antiprotozoal medications, such as paromomycin, or nitazoxanide (Alinia)
However, keep in mind that response to medication for blastocystis infection varies greatly from person to person. And, because the symptoms you're having might be unrelated to blastocystis, it's also possible that any improvement may be due to the medication's effect on another organism.
Preparing for an appointment
You'll probably first see your primary care doctor. However, in some cases when you call to set up an appointment, you may be referred to an infectious disease specialist or someone who specializes in digestive system disorders (gastroenterologist).
Because appointments can be brief, it's a good idea to be well-prepared for your appointment. Here's some information to help you get ready for your appointment, and what to expect from your doctor.
What you can do
- Be aware of any pre-appointment restrictions. At the time you make the appointment, be sure to ask if there's anything you need to do in advance, such as restrict your diet.
- Note down any symptoms you're experiencing, even if they seem unrelated to the reason you have scheduled the appointment.
- Write down key personal information, including any major stresses or recent life changes. Let your doctor know if you've recently traveled out of the country, especially if you traveled to a developing country.
- Make a list of all medications, vitamins or supplements you're taking.
- Write down a list of questions to ask your doctor.
Preparing a list of questions can help you make the most of your time with your doctor. Some basic questions to ask your doctor include:
- What's the most likely cause of my symptoms?
- Are there other possible causes?
- Do I need any tests?
- What treatments are available, and which one do you recommend for me?
- Is there a generic alternative to the medicine you're prescribing me?
- Are there any brochures or other printed material that I can take home with me? What websites do you recommend?
In addition to the questions that you've prepared to ask your doctor, don't hesitate to ask additional questions during your appointment.
What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:
- When did you first begin experiencing symptoms?
- Do you have symptoms all the time or do they come and go?
- How severe are your symptoms?
- Does anything seem to improve your symptoms?
- What, if anything, appears to worsen your symptoms?
- Have you traveled out of the country recently?
- Do you have any other health conditions?
What you can do in the meantime
If your symptoms are related to blastocystis, they may go away on their own before you even see your doctor. Be sure to stay well-hydrated in the meantime. Oral rehydration solutions — available through drugstores and health agencies worldwide — can effectively replace lost fluids and electrolytes.
If oral rehydration solution isn't available, you can make your own by combining 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.
Anti-diarrheal medications aren't generally recommended, because they can make some diarrheal illnesses worse.