Stool Test: Bacteria Culture

What It Is

A stool (feces) sample can provide doctors with valuable information about what's going on when a child has a problem in the stomach, intestines, or other part of the gastrointestinal (GI) system. A stool culture helps the doctor see if there's a bacterial infection in the intestines.

A technician places small stool samples in sterile plastic dishes with nutrients that encourage the growth of certain bacteria. The targeted bacteria will only grow if they're already in the stool sample. If bacterial colonies form, the technician evaluates them using a microscope and chemical tests to identify the organism.

Why It's Done

A doctor may request a stool culture to look for illness-causing bacteria such as:

Sometimes, other bacteria are found.

The stool culture might be ordered if your child has diarrhea for several days or has bloody diarrhea, especially if there's been an outbreak of foodborne illness in your community, your child has recently eaten undercooked meat or eggs or unpasteurized milk, or your child has recently traveled to certain places outside the United States.

Preparation

Unlike most other lab tests, a stool sample is usually collected by parents at home, not by health care professionals at a hospital or clinic. No special preparation is required, but tell your doctor if your child has recently taken antibiotics.

Procedure

The doctor or hospital laboratory will usually provide written instructions on how to collect a stool sample. If instructions aren't provided, here are tips for collecting a stool sample from your child:

Be sure to wear protective gloves and wash your hands and your child's hands afterward.
Many kids with diarrhea, especially young kids, can't always let a parent know in advance when a bowel movement is coming. So a hat-shaped plastic lid is used to collect the stool specimen. This catching device can be quickly placed over a toilet bowl, or under your child's bottom, to collect the sample. Using a catching device can prevent contamination of the stool by toilet water. Another way to collect a stool sample is to loosely place plastic wrap over the seat of the toilet. Then place the stool sample in a clean, sealable container before taking it to the lab.
Plastic wrap can also be used to line the diaper of an infant or toddler who isn't yet using the toilet. The wrap should be placed so that urine runs into the diaper, not the wrap.
Your child shouldn't urinate into the container. If possible, have your child empty his or her bladder before a bowel movement so the stool sample isn't diluted by urine.
The stool should be placed into clean, dry plastic jars with screw-cap lids. Your child may be asked to provide a stool sample one or more times. For best results, the stool should be brought to the lab within a few hours.

What to Expect

When the sample arrives at the laboratory, a technician smears stool samples on a growth-encouraging substance inside sterile plates. These plates are each kept at a temperature that ensures the quickest growth of targeted bacteria.

If no bacterial colonies form, the test is negative, meaning that there's no sign of a bacterial infection. But if bacterial colonies do form, the technician examines them under a microscope and may perform chemical tests to identify them more specifically.

Getting the Results

In general, the result of the stool culture is reported within 24 to 48 hours.

Risks

No risks are associated with collecting stool samples.

Helping Your Child

Collecting a stool sample is painless. Tell your child that collecting the stool won't hurt, but it has to be done carefully. A child who's old enough might be able to collect the sample alone to avoid embarrassment. Tell your child how to do this properly.