Collection and transport of stool specimens

Stool specimens are often required for the diagnosis and treatment of various gastrointestinal infections and disorders. These include bacterial, viral, parasitic and fungal infections, as well as inflammatory bowel diseases, malabsorption syndromes, colorectal cancer and other conditions. Stool specimens can also be used to monitor the effectiveness of therapy and to detect drug resistance.

However, stool specimens are highly susceptible to degradation and contamination by environmental factors, such as temperature, humidity, oxygen, light and microorganisms. Therefore, it is essential to collect and transport stool specimens in a proper manner to ensure their quality and reliability. Improper collection and transport of stool specimens can lead to false negative or false positive results, misdiagnosis, delayed treatment, increased morbidity and mortality, and unnecessary costs.

Some of the factors that affect the quality of stool specimens are:

• The timing of collection: Stool specimens should be collected as soon as possible after the onset of symptoms or as instructed by the clinician. Delayed collection can result in loss of pathogens or changes in their morphology and viability.
• The amount and type of specimen: Stool specimens should contain at least 5 g of faeces and include any parts that contain blood, mucus or pus. These parts may contain higher concentrations of pathogens or diagnostic markers. The specimen should not be contaminated with urine or water, as these can dilute or alter the specimen.
• The container and label: Stool specimens should be placed in a suitable container with a leakproof lid and clearly labeled with the patient`s name, identification number, date and time of collection, and any relevant clinical information. The container should be clean and sterile to prevent contamination from other sources.
• The transport medium: Stool specimens should be delivered to the clinic or laboratory within 2 hours of collection. If this is not possible, a small amount of the specimen should be transferred to a transport medium that preserves the pathogens or their antigens. Different transport media are available for different types of pathogens, such as Cary–Blair, Stuart or Amies media for bacteria; alkaline peptone water for Vibrio spp.; glycerol–phosphate buffer for viruses; and polyvinyl alcohol or formalin for parasites.
• The storage and transport conditions: Stool specimens should be stored and transported at low temperatures (2–8°C) to prevent bacterial overgrowth, viral inactivation or parasitic degradation. They should also be protected from light and excessive heat or cold. They should be delivered to the laboratory as soon as possible after collection or within 24 hours if stored in a refrigerator.

Collecting stool samples correctly is essential for obtaining accurate results from laboratory tests. Stool samples can be used to diagnose various gastrointestinal infections and disorders, such as bacterial, viral or parasitic infections, inflammatory bowel disease, malabsorption syndromes and colorectal cancer. Therefore, it is important to follow these steps when collecting stool samples:

• Provide the patient with two small wooden sticks and a suitable container with a leakproof lid. The container can be a clean glass cup, a plastic or waxed-cardboard box, or a special container with a spoon attached to the lid. Avoid using penicillin bottles, matchboxes and banana leaves as they can expose the laboratory staff to the risk of infection.
• Instruct the patient to collect the stool specimen on a piece of toilet tissue or old newspaper and to transfer it to the container, using the two sticks. The specimen should contain at least 5 g of faeces and, if present, those parts that contain blood, mucus or pus. It should not be contaminated with urine.
• Label the container with the patient`s name, date of birth, date and time of collection and any relevant clinical information.
• Advise the patient to wash their hands thoroughly after collecting the specimen.
• If possible, ask the patient to deliver the specimen to the clinic immediately after collection. If not, store the specimen in a cool place (e.g. a refrigerator) until delivery. Do not freeze the specimen.

Once the stool specimen has been collected and sealed in a suitable container, it should be transported to the clinic or laboratory as soon as possible. The sooner the specimen is examined, the more accurate and reliable the results will be.

Some factors that can affect the quality of the specimen during transport are:

• Temperature: High temperatures can cause bacterial overgrowth or death, which can alter the microbiological and chemical characteristics of the stool. Low temperatures can also affect some parasites and viruses. Ideally, the specimen should be kept at 4°C (refrigerated) or at room temperature (not exceeding 25°C) during transport.
• Time: The longer the specimen is stored before examination, the more likely it is that some pathogens will die or multiply, or that some substances will degrade or change. For example, trophozoites of Entamoeba histolytica can die within 30 minutes of collection, while Salmonella and Shigella can multiply rapidly in warm conditions. Some biochemical tests, such as reducing substances and pH, should be performed within 2 hours of collection. Therefore, it is recommended that the specimen be delivered to the laboratory within 2 hours of its collection, or within 24 hours if refrigerated.
• Labeling: The specimen container should be clearly labeled with the patient`s name, identification number, date and time of collection, and any relevant clinical information. This will help to avoid confusion and errors in the laboratory. The label should be attached to the container itself, not to the lid or the bag.
• Packaging: The specimen container should be placed in a leakproof plastic bag with a biohazard symbol. The bag should be sealed and placed in a rigid box or cooler with ice packs or cold packs to maintain a low temperature. The box or cooler should also have a biohazard symbol and a label with the sender`s name and address and the receiver`s name and address. The box or cooler should be handled with care and delivered by a reliable courier service or by hand.

Sometimes, it may not be possible for the patient to deliver the stool specimen to the clinic or laboratory within 2 hours of its collection. This may happen due to various reasons, such as distance, lack of transportation, or unavailability of the clinic or laboratory staff. In such cases, alternative methods for specimen transport should be used to preserve the quality and integrity of the specimen and to prevent the loss or overgrowth of pathogens.

One alternative method is to use a transport medium that can keep the pathogens viable for a longer period of time. Transport media are special solutions that provide nutrients and buffer the pH of the specimen. Some examples of transport media are Cary–Blair, Stuart or Amies media, which can be used for most bacterial pathogens. For cholera and other Vibrio spp., alkaline peptone water is an excellent transport (and enrichment) medium. To use a transport medium, a small amount of the faecal specimen (together with mucus, blood and epithelial threads, if present) should be collected on two or three swabs and placed in a container with the transport medium. Pathogens may survive in such media for up to 1 week, even at room temperature, although refrigeration is preferable.

Another alternative method is to use a preservative that can prevent the growth of bacteria and fungi and preserve the morphology of parasites. Preservatives are chemical substances that are added to the stool specimen in a certain ratio. Some examples of preservatives are 10% formalin, sodium acetate–acetic acid–formalin (SAF), polyvinyl alcohol (PVA), and merthiolate–iodine–formaldehyde (MIF). To use a preservative, a portion of the stool specimen should be mixed with an equal volume of the preservative in a leakproof container. Preservatives can keep the specimen stable for several days or weeks, depending on the type of preservative and the storage temperature.

Both transport media and preservatives have advantages and disadvantages. Transport media can maintain the viability of pathogens, but they may also allow the growth of contaminants or normal flora. Preservatives can prevent contamination and preserve morphology, but they may also kill or inhibit some pathogens or interfere with some laboratory tests. Therefore, it is important to consult with the laboratory staff before choosing an alternative method for specimen transport and to follow their instructions carefully.

Rectal swabs are sometimes used to collect stool specimens when the patient cannot produce a sufficient amount of faeces or when the specimen needs to be transported over a long distance. Rectal swabs can also be used to detect certain pathogens that may be present in the rectum, such as Neisseria gonorrhoeae, Chlamydia trachomatis, or Clostridioides difficile.

To collect a rectal swab, follow these steps:

• Wash your hands with soap and water and put on gloves.
• Explain the procedure to the patient and obtain their consent. Ask them to lie on their side with their knees bent or to stand and bend forward over a table or bed.
• Moisten a cotton-tipped swab with sterile water or saline. Do not use antiseptics or lubricants as they may interfere with the test results.
• Gently insert the swab through the rectal sphincter, about 2–3 cm (1 inch) deep. Rotate the swab gently and withdraw it slowly. Avoid touching the skin around the anus with the swab.
• Examine the swab for faecal staining and repeat the procedure until sufficient staining is evident. The number of swabs to be collected will depend on the number and types of investigation required. Usually, one or two swabs are enough for most tests.
• Place the swab in an empty sterile tube with a cotton plug or screw-cap, if it is to be processed within 1–2 hours. Label the tube with the patient`s name, date, and time of collection.
• If the swab must be kept for longer than 2 hours, place it in transport medium. Different transport media are available for different types of tests. For example, Cary–Blair, Stuart or Amies media are suitable for bacterial culture, while alkaline peptone water is recommended for Vibrio spp. detection. Follow the manufacturer`s instructions for using the transport medium and label the tube accordingly.
• Store and transport the swab at 2–8°C (36–46°F) until it reaches the laboratory. Do not freeze the swab as this may kill some pathogens.

Rectal swabs are often used to collect specimens for the diagnosis of enteric infections, such as salmonella, shigella, campylobacter, and yersinia. However, rectal swabs can also be used to detect other pathogens, such as Clostridium difficile, Helicobacter pylori, and sexually transmitted infections.

To ensure the quality and reliability of the laboratory results, rectal swabs must be stored and transported properly. Here are some general guidelines for the storage and transport of rectal swabs:

• Label the swab container with the patient`s name, identification number, date and time of collection, and type of test requested.
• If the swab is placed in an empty sterile tube, it should be refrigerated at 2–8°C and processed within 1–2 hours of collection. If refrigeration is not available, the swab should be kept at room temperature and processed as soon as possible.
• If the swab is placed in a transport medium, such as Cary–Blair, Stuart or Amies, it can be stored at room temperature for up to 48 hours. However, refrigeration at 2–8°C is preferable to prevent bacterial overgrowth and preserve viability. The transport medium should cover the tip of the swab completely.
• For cholera and other Vibrio spp., alkaline peptone water is an excellent transport (and enrichment) medium. The swab should be immersed in the medium and stored at room temperature for up to 24 hours. Refrigeration is not recommended for Vibrio spp., as it may inhibit their growth.
• Avoid freezing or exposing the swab to direct sunlight or heat, as this may damage or kill the microorganisms.
• Transport the swab to the laboratory in a sealed plastic bag or a leakproof container. Use appropriate biosafety precautions to prevent exposure or contamination.
• If the swab is delayed in transit or cannot be processed within the recommended time frame, it should be cultured on a selective agar plate and incubated at 35–37°C until processing. This may increase the recovery rate of some pathogens, such as shigella and campylobacter.

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