Gastrointestinal Pathogens Panel

Gastrointestinal (GI) pathogen panels are used to simultaneously test for the presence of multiple disease-causing (pathogenic) viruses, bacteria, and/or parasites in a stool sample and help diagnose an infection of the digestive system (GI tract). Since there are many causes of GI infections, a GI pathogen panel may be used in conjunction with other tests, such as a stool culture or an ova and parasite exam (O&P), to help establish a diagnosis.

The GI pathogen panel detects the genetic material (DNA, RNA) of the microbes that are tested. The number and type of microbes tested depend on the composition of the panel used. While some panels may be limited to testing for a few bacteria that are the most common causes of GI infections, for example, other panels may be more comprehensive and test for a variety of bacteria, viruses, and parasites.

Examples of some of the microbes that might be tested include:

• Viruses, such as norovirus or adenovirus
• Bacteria, such as Campylobacter, Salmonella or Clostridium difficile
• Parasites, such as Giardia or Cryptosporidium

Many GI infections in the U.S. resolve with no specific treatment, with only supportive care, and may not require testing. In otherwise healthy individuals, the infections are considered common illnesses that are not serious and sometimes thought of as “food poisoning” or “stomach flu.” However, there are cases where it is useful to perform testing that identifies the cause of the GI infection – to guide its treatment, eliminate its source, and limit its spread.

The panels may identify the presence of microbes that a healthcare practitioner might not otherwise suspect and identify co-infections (more than one cause for the infection). This allows treatment (when needed) to be better targeted and to begin sooner. Results of testing may be available within a few hours.

Since the GI panels are relatively new, laboratories and healthcare providers are still in the process of determining how to use them to provide the optimum patient results while being cost-effective. Additional tests, such as stool culture and O&P, may be done if a microbe is not identified by the panel and/or if there is a suspicion of a microbe other than those included in the GI panel.

GI panels are not used to monitor the effectiveness of treatment. Once the specific microbe(s) causing the infection has been identified, a test that is specific for the microbe(s) would be used instead of a GI panel to determine whether treatment has cured the infection. This may be done, for example, when there is an outbreak of foodborne illness. Food handlers would have follow-up testing to ensure that they are no longer shedding the pathogen and will not spread it to others.

GI panels may be ordered when a person has signs and symptoms associated with a digestive system infection. These may include:

• Diarrhea with frequent, loose stools
• Blood and/or mucus in the stool in some cases
• Stomach (abdominal) pain and cramping
• Nausea and vomiting
• Fever

Not everyone who has these symptoms will necessarily have testing done or be treated. In people with healthy immune systems, these infections often resolve with supportive care and without treatment. A GI pathogen panel is more likely to be ordered when a person:

• Has severe symptoms, dehydration, electrolyte imbalance, and other complications
• Is very young, elderly, or has a weakened immune system
• Has prolonged signs and symptoms and/or infections that do not resolve without treatment
• Has an illness during and following travel outside the U.S, especially to emerging nations
• Is ill and a possible outbreak of food or waterborne illness prompts the medical community to investigate and identify the cause; examples include contaminated produce, contaminated food from a specific restaurant, and/or illness on a cruise ship.

Results are typically interpreted in conjunction with a person’s signs and symptoms, medical history, and travel history.

A positive result means that the microbe detected and identified is likely causing the signs and symptoms. If more than one result is positive, the person may be infected with more than one microbe (co-infection). The following are some exceptions:

• Sometimes, a positive result reflects the presence of bacteria that are present in (colonize) a person’s digestive system but do not cause illness.
• The panels detect the presence of genetic material of the microbes and do not distinguish between dead and living ones. Sometimes, a positive result reflects the presence of dead microbes that are not the cause of infection.
• Rarely, a result may be positive when the microbe is not present or may show positive as a different organism because of genetic similarities.

A negative result means that the microbes tested were not detected and the person’s signs and symptoms may be caused by a condition other than an infection or a pathogen that was not tested for. The following are some exceptions:

• When a person has a GI infection caused by a less common bacterium, parasite, or virus not included in the panel, then it will not be detected.
• Microbes are shed into the stool intermittently. A negative result may mean that the microbe causing the person’s infection was not present in the stool at the time the sample was collected.
• Rarely, a person may have a GI infection caused by one of the microbes, but the test does not detect it. The bacteria, virus, or parasite genetic material may be present in very small quantities in the stool sample.

If results are negative and symptoms persist and/or if suspicion of an infection remains high, then other tests may be done to help establish a diagnosis:

• A GI pathogens panel only detects a few of the common parasites. An O&P exam may need to be performed as a follow-up test if a parasite that is not on the panel is suspected. Less common parasites are more frequently encountered when someone has traveled outside of the U.S. but are also found within the U.S.
• A stool culture may be done as a follow-up test to detect bacteria that are not included in the panel.

Unlike the stool culture, GI panels do not grow bacteria so there will not be live bacteria available to perform susceptibility testing on to help guide antimicrobial selection. If susceptibility testing is needed, then the bacteria will also need to be cultured.

When a health care practitioner has a strong suspicion as to the cause of an infection, then a test for a specific microbe may be ordered instead of a panel. Examples include:

• A person has drunk water from a stream while camping and is likely to be infected with Giardia. A Giardia antigen test may be performed.
• Someone recently completed treatment that involved a broad-spectrum antimicrobial and is likely to have a Clostridium difficile infection. A Clostridium difficile toxin or PCR test may be performed.

No, it requires specialized equipment and expertise. It may be performed in a local laboratory if it is offered or may need to be sent to a reference laboratory.

Additional testing may be done to confirm a positive result using another method, to perform susceptibility testing when required, or because the cause of your symptoms has not yet been identified.

It is not always possible to prevent a GI infection, but there are things that you can do to lower your risk. The best things to do are to not drink water or eat food that may be contaminated and to follow good sanitation practices, such as thorough and frequent hand washing. Food that might be contaminated, such as raw meats and eggs, should be cooked thoroughly. Dairy products should be pasteurized. Cooked foods and foods that are served raw should not touch any surfaces that may have been contaminated. If someone in your household has an infection that is causing diarrhea, careful hand washing by all family members is recommended, commonly touched surfaces should be disinfected, and the person infected should not prepare food or drink for others until the infection is resolved.

When you are traveling to developing nations, it is best to only drink bottled water, carbonated drinks, and hot cooked foods. Avoid fresh fruits and vegetables, limiting yourself to those that you can peel yourself. Food from street vendors is generally not considered safe. The Centers for Disease Control and Prevention has an excellent resource for travelers: CDC Health Information for International Travel (the Yellow Book).

Some of the bacteria strains encountered have been previously ingested by local inhabitants, who are now immune to these pathogens, but cause gastrointestinal distress to the tourist.