Lab result explainedInflammationLast updated November 11, 2026

Stool culture and GI pathogen panel: results, what they test for and how long they take

Stool culture · Stool test (often ordered with C. diff testing, ova and parasites, and fecal calprotectin or lactoferrin) · reported in Qualitative: organism isolated or not isolated (culture); detected or not detected for each target (PCR panel)

A stool culture is a laboratory test that grows bacteria from a sample of diarrhea to find out whether an infection is causing it. A routine US stool culture looks for four groups of bacteria: Salmonella, Shigella, Campylobacter and Shiga toxin-producing E. coli (STEC, including O157:H7). Other organisms such as Yersinia, Vibrio and Aeromonas are looked for only if requested or if your history (raw shellfish, travel, pork) suggests them. A normal result reads 'no enteric pathogens isolated' or 'normal fecal flora', which means none of the targeted bacteria grew.

Many labs now run a gastrointestinal (GI) pathogen panel instead of, or alongside, culture. This is a PCR test that detects the genetic material of 12 to 22 organisms at once, bacteria, viruses (norovirus, rotavirus, adenovirus, astrovirus, sapovirus) and parasites (Giardia, Cryptosporidium, Cyclospora, Entamoeba histolytica), in one to five hours. The panel finds a cause in 30 to 50 percent of samples compared with 2 to 5 percent for culture alone, mostly because most infectious diarrhea is viral, which culture cannot see. The trade-off is that PCR also picks up organisms that are present without causing illness.

Most bouts of diarrhea do not need a stool test at all: they are viral, last under a week and settle with fluids. Testing is recommended when there is fever, blood or mucus in the stool, severe abdominal pain, signs of dehydration, diarrhea lasting more than 7 days, a weakened immune system, recent travel, a possible outbreak, or when the person works in food handling or healthcare. Culture results take 48 to 72 hours, with a preliminary report sometimes at 24 hours; PCR panels are usually reported the same day.

Stool culture at a glance

What it is: a stool sample grown on selective media (culture) or tested by PCR (GI pathogen panel) to identify bacteria, and on panels also viruses and parasites, that cause diarrhea.
Normal result: 'no enteric pathogens isolated', 'normal fecal flora' or 'not detected' for every target.
Routine culture targets: Salmonella, Shigella, Campylobacter and Shiga toxin-producing E. coli; Yersinia, Vibrio and Aeromonas on request.
How long: culture 2 to 3 days (final negative report up to 3 to 5 days); PCR panel 1 to 5 hours, usually reported the same day.
Positive result: names the organism; some need antibiotics (Shigella, severe Campylobacter), some do not (most Salmonella), and antibiotics are avoided in STEC because they can trigger hemolytic uremic syndrome.
Negative result with ongoing diarrhea: think viral infection already clearing, C. difficile (separate test), parasites, medication, inflammatory bowel disease or post-infectious irritable bowel.

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What Stool culture measures

In a conventional culture, a small amount of stool is spread onto several agar plates designed to suppress the trillions of normal gut bacteria and favor the pathogens of interest: for example, a Campylobacter plate incubated at 42 °C in low oxygen, a Hektoen or xylose-lysine plate that turns Salmonella and Shigella colonies distinctive colors, and sorbitol-MacConkey agar on which E. coli O157 fails to ferment sorbitol. Suspicious colonies are identified by biochemical tests or mass spectrometry, and Shiga toxin is detected by an immunoassay or PCR. Antibiotic susceptibility can then be tested on the isolate, which is one advantage culture keeps over PCR.

A GI pathogen panel extracts DNA and RNA from the stool and amplifies gene sequences unique to each organism. The FDA-cleared multiplex panels detect between 12 and 22 targets with sensitivities above 90 to 95 percent for most of them. Because PCR detects genetic material rather than living organisms, it stays positive for days to weeks after an infection has resolved and it detects carriage of organisms such as enteropathogenic E. coli (EPEC) and enteroaggregative E. coli (EAEC) that are found in healthy people too, so a positive for those targets is interpreted cautiously. When a panel detects Salmonella, Shigella, STEC or Vibrio, public health rules usually require the lab to culture the sample as well so the strain can be typed for outbreak tracking.

Collection matters. The sample should be fresh liquid or soft stool caught in a clean container or on plastic wrap over the toilet, not scooped from toilet water or mixed with urine, and transferred into the transport vial (usually Cary-Blair medium) within an hour or two. Formed stool is often rejected because the yield is negligible. One sample is adequate in most cases; a second adds little. Many hospitals also apply the '3-day rule': stool from someone who has already been in hospital for more than three days is tested for C. difficile instead of culture, because community pathogens are almost never the cause by then.

Normal range for Stool culture

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (Qualitative: organism isolated or not isolated (culture); detected or not detected for each target (PCR panel))	Notes
No enteric pathogens isolated / normal fecal flora	Negative culture	None of the targeted bacteria grew. It does not exclude viruses, parasites or C. difficile, which need their own tests, and about 1 in 20 true bacterial infections is missed by a single culture.
GI pathogen panel: not detected	Negative for all 12–22 targets	A strong negative. Covers the common viruses and parasites as well as bacteria; a negative panel in acute diarrhea usually means a non-infectious or already-cleared cause.
Campylobacter species isolated or detected	Positive	The most common bacterial cause of diarrhea in the US. Usually self-limited in 5 to 7 days; antibiotics are reserved for severe or prolonged illness and high-risk people.
Salmonella species isolated or detected	Positive	Non-typhoidal Salmonella generally resolves without antibiotics, which can prolong carriage; they are used for infants under 3 months, people over 65, the immunocompromised and anyone with severe disease or bloodstream spread.
Shigella species isolated or detected	Positive	Highly contagious (as few as 10 organisms). Antibiotics shorten illness and shedding; susceptibility testing matters because resistance is common. Reportable to public health.
Shiga toxin-producing E. coli (STEC / E. coli O157)	Positive, with Shiga toxin 1 or 2	Antibiotics and anti-motility drugs are avoided because they raise the risk of hemolytic uremic syndrome, which develops in 5 to 10 percent of children. Kidney function and blood counts are monitored for about 2 weeks.
Yersinia, Vibrio, Aeromonas or Plesiomonas	Positive (special request or panel)	Yersinia from undercooked pork can mimic appendicitis; Vibrio follows raw oysters or seawater exposure; Aeromonas and Plesiomonas follow freshwater or travel.
Viral target detected (norovirus, rotavirus, adenovirus 40/41, astrovirus, sapovirus)	Positive on PCR panel only	No antibiotics help. Norovirus is the leading cause of gastroenteritis in the US at all ages; rotavirus and adenovirus mostly affect young children.
EPEC, EAEC or ETEC detected	Positive on PCR panel only	These E. coli types are found in a meaningful share of healthy people, so a positive is weighed against symptoms, travel history and whether anything else was found. ETEC is the classic cause of travelers' diarrhea.

Positive stool culture or pathogen detected

A positive stool culture means one of the targeted bacteria grew from your sample and is the likely cause of your diarrhea. The report names the organism, and for culture usually lists which antibiotics it is sensitive to. Which organism it is decides what happens next: Campylobacter and non-typhoidal Salmonella usually clear on their own within a week and antibiotics are reserved for severe illness or high-risk people, Shigella is generally treated to shorten illness and stop spread, and Shiga toxin-producing E. coli is deliberately not treated with antibiotics because they increase the chance of hemolytic uremic syndrome, a kidney complication that mainly affects children under 5 and adults over 65.

On a PCR panel, a positive is a little more nuanced. A detection of Salmonella, Shigella, Campylobacter, STEC, Vibrio, norovirus, rotavirus, Giardia or Cryptosporidium in someone with matching symptoms is almost always the real cause. A detection of EPEC, EAEC, Clostridioides difficile toxin genes or Blastocystis is less certain, because these are carried by a proportion of healthy people, and about 1 in 5 positive panels lists two or more organisms, in which case the clinician decides which one fits. PCR also stays positive for weeks after recovery, so it is not used to confirm that an infection has cleared.

Nearly all positive results are reported to the local health department, which may call to ask about food, water, travel and contacts; this is how outbreaks are found. People who handle food, work in healthcare or childcare, or attend daycare are usually asked to stay off until symptoms have resolved for 24 to 48 hours, and for Shigella, STEC and typhoid Salmonella some jurisdictions require negative follow-up cultures before return.

Common causes

Campylobacter jejuni
Undercooked poultry, raw milk, untreated water and contact with puppies; about 1.5 million US infections a year. Causes cramping, fever and often bloody diarrhea 2 to 5 days after exposure. Roughly 1 in 1,000 cases is followed by Guillain-Barré syndrome and 1 to 5 percent by reactive arthritis.
Non-typhoidal Salmonella
Eggs, poultry, raw produce, peanut butter and reptile or backyard-chicken contact; 1.35 million US infections a year. Diarrhea, fever and cramps for 4 to 7 days; the bacteria spread to the blood in about 5 percent, more in infants, older adults and people with sickle cell disease or immune suppression.
Shigella
Spread person to person via tiny amounts of stool, in daycare centers, among men who have sex with men, and in travelers. Causes fever, cramping and small-volume bloody, mucoid stools with urgency (dysentery). Increasingly resistant to common antibiotics.
Shiga toxin-producing E. coli (O157:H7 and non-O157)
Undercooked ground beef, raw leafy greens, sprouts, unpasteurized juice and petting zoos. Severe cramps and bloody diarrhea, usually without high fever. Hemolytic uremic syndrome (anemia, low platelets, kidney failure) follows in 5 to 10 percent, typically a week after diarrhea starts.
Yersinia enterocolitica
Raw or undercooked pork, especially chitterlings, and unpasteurized milk. Diarrhea and right-sided abdominal pain that mimics appendicitis, mostly in children; reactive arthritis and erythema nodosum can follow.
Vibrio species
Raw or undercooked oysters and other shellfish, or wounds exposed to warm coastal water. Vibrio parahaemolyticus causes watery diarrhea; Vibrio vulnificus can cause life-threatening bloodstream infection in people with liver disease.
Norovirus and other viruses (PCR panel)
Norovirus causes about 20 million US illnesses a year with sudden vomiting and watery diarrhea lasting 1 to 3 days; rotavirus, adenovirus 40/41, astrovirus and sapovirus mostly affect young children. None respond to antibiotics.
Travelers' diarrhea organisms
Enterotoxigenic E. coli (ETEC) is the leading cause of diarrhea after travel to lower-income countries, followed by Campylobacter, Shigella, Salmonella and, for illness lasting more than 2 weeks, Giardia.
Parasites detected on a panel
Giardia, Cryptosporidium, Cyclospora and Entamoeba histolytica are included on most panels. They are discussed on the ova and parasites page; Cryptosporidium and Cyclospora are the ones most often missed by conventional stool microscopy.
Colonization or recently cleared infection (PCR only)
EPEC and EAEC are found in up to 10 to 20 percent of healthy children's stools; C. difficile genes are carried by 5 to 15 percent of hospital patients. A PCR positive for these without matching symptoms, or weeks after recovery, may not be the cause of current symptoms.

Symptoms that can go with it

Watery diarrhea, often sudden, with cramping and urgency
Bloody or mucoid stools, which point to Shigella, Campylobacter, STEC or Entamoeba and are the main reason culture is ordered
Fever and chills, more typical of bacterial than viral causes
Nausea and vomiting, which dominate in norovirus and in Salmonella and staphylococcal food poisoning
Signs of dehydration: thirst, dark urine, dizziness on standing, dry mouth, little or no urine in children
Severe right-sided or diffuse abdominal pain, sometimes mistaken for appendicitis (Yersinia, Campylobacter)
Later complications: joint pain 1 to 4 weeks after the illness (reactive arthritis), tingling or weakness in the legs (Guillain-Barré syndrome after Campylobacter), pallor, bruising and reduced urine a week into an STEC infection (hemolytic uremic syndrome)

Read it alongside

C. difficile test — ordered on its own, especially after antibiotics or more than 3 days in hospital; routine culture does not look for it.
Ova and parasites or Giardia/Cryptosporidium antigen — for diarrhea lasting more than 7 to 14 days, after travel or camping, or in daycare settings.
Fecal calprotectin or lactoferrin — markers of gut inflammation; high levels with a negative culture raise the question of inflammatory bowel disease.
Complete blood count — a high white count suggests bacterial infection; a falling hemoglobin and platelet count in an STEC infection signals hemolytic uremic syndrome.
Creatinine, BUN, sodium, potassium and bicarbonate — show dehydration and kidney strain, and are monitored for 2 weeks after an STEC diagnosis.
Blood cultures — drawn when fever is high or the person is very unwell, because Salmonella, Campylobacter and Yersinia can enter the bloodstream.
Fecal immunochemical test (FIT) — not for infection, but visible blood that persists after an infection has cleared needs a different explanation.

What usually happens next

Most people with a negative result and improving symptoms need nothing further: fluids, normal food as tolerated and time. Antidiarrheal medicines are avoided if there is fever or blood in the stool.
If the result is positive, your clinician decides whether antibiotics help based on the organism, your age, immune status and severity; for Salmonella and Campylobacter the usual answer in otherwise healthy adults is no, and for STEC it is a firm no.
Expect a call from the health department for Salmonella, Shigella, STEC, Vibrio, Yersinia and Campylobacter; food handlers, healthcare and childcare workers may be asked to stay home until cleared.
After an STEC result, children in particular are watched for 2 weeks with blood counts and kidney tests for hemolytic uremic syndrome; pallor, bruising, swelling or reduced urine should be reported immediately.
If diarrhea has lasted more than 7 days with a negative culture, the next tests are usually C. difficile, ova and parasites or a PCR panel if not already done, fecal calprotectin, celiac serology and a medication review; beyond 4 weeks, colonoscopy is often considered.
Do not ask for a repeat culture to prove the infection has gone unless public health or your employer requires it; bacteria can be shed for weeks after symptoms resolve and PCR for even longer.

Diet, lifestyle and natural levers with evidence

What can move Stool culture once the cause is known. Nothing here replaces finding the cause.

Oral rehydration solution

Strong evidence

Fluid and salt loss, not the bacteria, is what makes infectious diarrhea dangerous. Glucose-electrolyte oral rehydration solution uses the gut's sodium-glucose transporter, which keeps working during infection, and in trials of reduced-osmolarity ORS it cut the need for intravenous fluids by about a third and stool output by about 20 percent compared with older formulas. It is credited with preventing tens of millions of child deaths worldwide. Sports drinks and juice have too much sugar and too little sodium; pharmacy ORS sachets or the WHO recipe are the evidence-based option.

Seek care rather than relying on ORS if you cannot keep fluids down, are passing very little urine, or are confused or faint.

Early normal eating rather than a restricted diet

Moderate evidence

Trials in children show that resuming an age-appropriate normal diet within 4 to 6 hours of starting rehydration shortens illness slightly and improves weight recovery compared with prolonged fasting or a bland 'BRAT' diet, which is low in protein and calories and is no longer recommended by the American Academy of Pediatrics. Fatty, very sugary and spicy foods are often less well tolerated for a few days, and a temporary intolerance of milk sugar is common after rotavirus and Giardia.

Hand washing with soap and safe food handling

Strong evidence

Nothing natural changes a culture result, but household spread can be prevented. A Cochrane review of hand-washing promotion found it reduced diarrhea episodes by about 30 percent. Shigella and norovirus spread with tiny doses, so soap-and-water washing after the toilet and before food, cleaning bathroom surfaces, and not preparing food for others while symptomatic are the key measures. Cooking poultry to 165 °F and ground beef to 160 °F, avoiding raw milk and raw sprouts, and keeping raw meat away from ready-to-eat food prevent most Campylobacter, Salmonella and STEC infections.

Zinc for children in low-income settings

Moderate evidence

The WHO recommends 10 to 20 mg of zinc a day for 10 to 14 days for children over 6 months with acute diarrhea. A Cochrane review found it shortens diarrhea by about half a day in children over 6 months in regions where zinc deficiency is common, with no clear benefit in well-nourished children in high-income countries. It causes vomiting in a minority.

Probiotics (Lactobacillus rhamnosus GG, Saccharomyces boulardii)

Preliminary evidence

Older, smaller trials suggested probiotics shortened infectious diarrhea by about a day, but two large 2018 US and Canadian trials of Lactobacillus rhamnosus GG in nearly 1,900 children with acute gastroenteritis found no benefit, and the 2020 Cochrane update concluded that probiotics probably make little or no difference to how long diarrhea lasts. Saccharomyces boulardii has somewhat more consistent, modest evidence in adults and in travelers' diarrhea prevention.

Avoid probiotics in people with central venous lines, severe immune suppression or critical illness, in whom bloodstream infection with the probiotic organism has been reported.

When to see a clinician promptly

Signs of dehydration: dizziness or fainting on standing, very little or no urine for 8 hours, confusion, a very dry mouth, or in a baby no wet diaper for 6 hours, no tears, or a sunken soft spot: these need same-day care, urgently in infants and older adults.
Bloody diarrhea with a fever above 102 °F (38.9 °C), or six or more unformed stools in 24 hours with severe abdominal pain.
After a confirmed or suspected STEC infection, especially in a child: pallor, unusual tiredness, bruising, swelling or reduced urine output, which can mean hemolytic uremic syndrome and needs emergency assessment.
Diarrhea in someone who is pregnant, over 70, immunosuppressed (chemotherapy, transplant, HIV with low CD4) or has inflammatory bowel disease, in whom infections are more often severe.
Diarrhea lasting more than 7 days, or any diarrhea with weight loss or waking you at night.
New weakness, tingling in the feet or difficulty walking in the weeks after a diarrheal illness, which can be the start of Guillain-Barré syndrome.

Frequently asked questions

How long does a stool culture take?

Conventional culture takes 48 to 72 hours for bacteria to grow and be identified, and a final negative report can take 3 to 5 days because slow-growing organisms are given time. Some labs issue a preliminary result at 24 hours. A PCR-based GI pathogen panel takes 1 to 5 hours to run and is usually reported the same day or the next morning. Antibiotic susceptibility results on a cultured organism add another day.

What does 'normal fecal flora' or 'no enteric pathogens isolated' mean?

It means your sample grew the ordinary mixture of gut bacteria and none of the disease-causing bacteria the lab looks for (Salmonella, Shigella, Campylobacter and Shiga toxin-producing E. coli). It is a negative result. It does not test for viruses, parasites or C. difficile, so if your symptoms continue your clinician may order those separately or a PCR panel that covers them.

My stool culture was negative but I still have diarrhea. What else could it be?

Most acute diarrhea is viral and will not show on a culture; it should be settling within a week. If it is not, the usual suspects are C. difficile (especially after antibiotics), parasites such as Giardia, medications (metformin, antibiotics, magnesium, PPIs, some blood pressure drugs), a flare of inflammatory bowel disease, celiac disease, bile acid diarrhea and post-infectious irritable bowel syndrome, which follows about 1 in 10 bacterial gut infections. A fecal calprotectin, a parasite test and a medication review are the common next steps.

What is the difference between a stool culture and a GI pathogen panel?

A culture grows live bacteria and can only find the handful of species the plates are designed for, but it yields an organism that can be tested for antibiotic sensitivity and typed for outbreak tracking. A GI pathogen panel detects the genetic material of 12 to 22 bacteria, viruses and parasites in hours and finds a cause far more often, but it cannot tell live from dead organisms, stays positive for weeks after recovery and detects some organisms that healthy people carry. Many labs run the panel first and reflex to culture when a reportable bacterium is detected.

Does a positive stool culture always need antibiotics?

No. Most Campylobacter and non-typhoidal Salmonella infections in healthy people resolve on their own within a week, and antibiotics for Salmonella can actually prolong the time you carry the bacteria. Shigella is usually treated because it is so contagious. Shiga toxin-producing E. coli is specifically not treated with antibiotics because they increase the risk of hemolytic uremic syndrome. Antibiotics are used for anyone severely ill, very young, elderly or immunosuppressed. Your clinician makes that call from the organism and your circumstances.

How do I collect a stool sample for culture?

Pass stool into a clean, dry container, a disposable collection 'hat' placed under the toilet seat, or onto plastic wrap stretched over the bowl; do not let it touch toilet water or mix with urine. Use the spoon in the lid to transfer stool into the vial up to the fill line (choose bloody or mucoid parts if present), screw the cap tightly and get it to the lab within an hour or two, or refrigerate it if the vial has preservative and you cannot deliver it straight away. Loose or watery stool is what the lab wants; formed stool is often rejected.

Why was my stool culture rejected or not done?

Labs reject samples that are formed rather than loose, that arrive too late or in the wrong container, that are contaminated with urine or water, or that come from someone who has been in hospital for more than 3 days, because community bacteria are almost never the cause by then and C. difficile testing is more appropriate. Some labs also decline repeat cultures within 7 days of a negative result because the yield is under 1 percent.

Can I go back to work or school with a positive stool culture?

Generally once you have had no diarrhea or vomiting for 24 to 48 hours, provided you wash your hands carefully. Food handlers, healthcare workers and childcare workers and attendees face stricter rules, and for Shigella, Shiga toxin-producing E. coli and typhoid Salmonella many health departments require one or two negative follow-up stool tests before return. Your local health department will tell you what applies.

References

Shane AL, Mody RK, Crump JA, et al.. 2017 Infectious Diseases Society of America clinical practice guidelines for the diagnosis and management of infectious diarrhea. Clinical Infectious Diseases (2017)
Riddle MS, DuPont HL, Connor BA. ACG Clinical Guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults. American Journal of Gastroenterology (2016)
Stool culture. MedlinePlus Medical Encyclopedia, US National Library of Medicine (2023)
Binnicker MJ. Multiplex molecular panels for diagnosis of gastrointestinal infection: performance, result interpretation, and cost-effectiveness. Journal of Clinical Microbiology (2015)
Buss SN, Leber A, Chapin K, et al.. Multicenter evaluation of the BioFire FilmArray gastrointestinal panel for etiologic diagnosis of infectious gastroenteritis. Journal of Clinical Microbiology (2015)
Bauer TM, Lalvani A, Fehrenbach J, et al.. Derivation and validation of guidelines for stool cultures for enteropathogenic bacteria other than Clostridium difficile in hospitalized adults. JAMA (2001)
Collinson S, Deans A, Padua-Zamora A, et al.. Probiotics for treating acute infectious diarrhoea. Cochrane Database of Systematic Reviews (2020)
Schnadower D, Tarr PI, Casper TC, et al.. Lactobacillus rhamnosus GG versus placebo for acute gastroenteritis in children. New England Journal of Medicine (2018)
Ejemot-Nwadiaro RI, Ehiri JE, Arikpo D, Meremikwu MM, Critchley JA. Hand-washing promotion for preventing diarrhoea. Cochrane Database of Systematic Reviews (2021)
Lazzerini M, Wanzira H. Oral zinc for treating diarrhoea in children. Cochrane Database of Systematic Reviews (2016)
Campylobacter infection (campylobacteriosis). Centers for Disease Control and Prevention (2024)
Overview of gastroenteritis. Merck Manual Professional Version (2024)

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This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.