Stool Culture

A stool culture is done to identify bacteria or viruses that may be causing an infection. Although more than 50 different kinds of bacteria normally live in the intestines, large numbers of abnormal bacteria, viruses, fungi, or parasites can grow in the intestines and cause infections and diseases.

For a stool culture, a stool sample is collected in a clean container and placed under conditions that allow bacteria or other organisms to grow. The type of infection is identified by noting the appearance of the growth, by performing chemical tests on the stool sample, and by looking at the sample under a microscope.

Usually several stool samples are collected over a period of days for accurate test results.

A stool culture is done to:

• Find the cause of symptoms, such as severe or bloody diarrhea, an increased amount of gas, nausea, vomiting, loss of appetite, bloating, abdominal pain and cramping, and fever.
• Find and identify certain types of bacteria, viruses, fungi, or parasites that are causing infections or diseases, such as food poisoning, inflammation of the large intestine (pseudomembranous enterocolitis), cholera, and typhoid.
• Identify a person who may not have any symptoms of disease but who carries bacteria that can spread infection to others. This person is called a carrier. A person who is a carrier and who handles food is likely to infect others.
• Find out if treatment for an infection has been effective.

No special preparation is required before having this test. Do not collect a stool sample if you have bleeding hemorrhoids. Women should not collect a stool sample during their menstrual period; wait until 3 days after your period has stopped. Tell your doctor if you have recently taken antibiotics, traveled out of your native country, or had a recent test with contrast material.

Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form(What is a PDF document?).

Stool samples can be collected at home, in your doctor's office, at a medical clinic, or at the hospital. If you collect the samples at home, you may be given a special container.

You may need to collect more than one sample. Follow the same procedure for each sample.

Collect the sample as follows:

• Urinate before collecting the stool so that you do not get any urine in the stool sample. Do not urinate while passing the stool.
• Put on gloves before handling your stool. Stool can contain material that spreads infection. Wash your hands after you remove your gloves.
• Pass stool (but no urine) into a dry container. You may be given a plastic basin that can be placed under the toilet seat to catch the stool.
  • Either solid or liquid stool can be collected.
  • If you have diarrhea, a large plastic bag taped to the toilet seat may make the collection process easier; the bag is then placed in a plastic container.
  • If you are constipated, you may be given a small enema.
  • Do not collect the sample from the toilet bowl.
  • Do not mix toilet paper, water, or soap with the sample.
• Place the lid on the container and label it with your name, your doctor's name, and the date the stool was collected. If you are collecting more than one sample, use one container for each sample, and collect a sample only once a day unless your doctor gives you other directions.

Take the sealed container to your doctor's office or the laboratory as soon as possible. You may need to deliver your sample to the lab within a certain time. Tell your doctor if you think you may have trouble getting the sample to the lab on time.

You may need to collect several stool samples over 7 to 10 days if you have digestive symptoms after traveling outside the country.

Samples from babies and young children may be collected from diapers (if the stool is not contaminated with urine) or from a small-diameter glass tube inserted into the baby's rectum while the baby is held on an adult's lap.

Sometimes a stool sample is collected using a rectal swab that contains a preservative. The swab is inserted into the rectum, rotated gently, and then withdrawn. It is placed in a clean, dry container and sent to the lab right away.

Collecting a stool sample does not normally cause any discomfort.

If your doctor collects the stool sample using a cotton swab, you may feel some pressure or discomfort as the cotton swab is inserted into your rectum.

There is no chance for problems while collecting a stool sample. Be sure to wear gloves when you collect the sample and wash your hands before and after you collect the sample. This will help protect you from spreading an infection.

A stool culture is done to identify bacteria, viruses, fungi, or parasites that may be causing an infection. Stool culture test results usually take 2 to 3 days.

If bacteria are found in the culture, sensitivity testing may be done to help choose the best treatment.

Reasons you may not be able to have the test or why the results may not be helpful include:

• Recent use of antibiotics, medicine (such as bismuth) to control diarrhea, enemas, or laxatives.
• Recent X-ray tests using a contrast material containing barium.
• A stool sample that is mixed with urine or blood.
• Not collecting a large enough sample.
• Not getting the stool sample to the lab for testing quickly enough.

• A stool culture may be ordered if you have diarrhea and drank untreated well or lake water or have been traveling to a rural area or outside of the country.
• You may still have an infection even if your stool culture test is normal.
• Sensitivity testing helps your doctor choose the best treatment for the specific disease or infection.
• A stool sample may be tested for parasites such as pinworms, roundworms, tapeworms and the protozoan Giardia that causes giardiasis. The parasites or their eggs can often be seen during an examination of the stool sample under a microscope. For more information, see the topics Pinworms or Giardiasis.
• A stool sample can also be checked for:
  • White blood cells, which may be caused by diseases such as inflammatory bowel disease.
  • Blood, which may be caused by ulcers or cancer of the colon.
  • Poisonous substances (toxins) produced by some types of bacteria.
• A stool analysis is a series of tests done on a sample of stool to help diagnose certain conditions affecting the digestive tract, including infection, poor absorption, or cancer. For more information, see the medical test Stool Analysis.

Other Works Consulted

• Chernecky CC, Berger BJ, eds. (2004). Laboratory Tests and Diagnostic Procedures, 4th ed. Philadelphia: Saunders.

• Fischbach FT, Dunning MB III, eds. (2004). Manual of Laboratory and Diagnostic Tests, 7th ed. Philadelphia: Lippincott Williams and Wilkins.

• Handbook of Diagnostic Tests (2003). 3rd ed. Philadelphia: Lippincott Williams and Wilkins.

• Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis: Mosby.