ConditionInfections
Infectious Gastroenteritis
Infectious gastroenteritis is inflammation of the stomach and intestines caused by a virus, bacterium or parasite, often called stomach flu or food poisoning. It causes diarrhea, vomiting, cramps and sometimes fever. Viruses such as norovirus cause most cases and clear in 1 to 3 days. Bacteria such as Salmonella, Campylobacter and E. coli are more likely to cause bloody diarrhea and fever. Rehydration is the main treatment; antibiotics are needed only in specific situations.
Also called: Stomach flu, stomach bug, gastro, infectious diarrhea, food poisoning
At a glance
- What it is
- A gut infection causing diarrhea, vomiting and cramps.
- Viruses (most cases)
- Norovirus, rotavirus, adenovirus, astrovirus.
- Bacteria
- Campylobacter, Salmonella, Shigella, E. coli, C. difficile, Vibrio.
- Parasites
- Giardia, Cryptosporidium, Entamoeba.
- Treatment
- Oral rehydration, rest, gradual return to food; antibiotics only in selected cases.
- Red flags
- Bloody diarrhea, high fever, signs of dehydration, symptoms lasting more than a week.
When to get help
Call 911 or go to the ER
- Signs of severe dehydration: no urine for 8 hours or more, extreme thirst, dizziness or fainting, a racing heart, confusion, or a very sleepy, floppy child
- Vomiting blood or green bile, or severe constant belly pain
- Bloody diarrhea with decreased urination, pale skin or unusual bruising, especially in a child (possible hemolytic uremic syndrome)
See a doctor within a day or two
- Bloody diarrhea
- Fever above 39 °C (102 °F)
- Unable to keep fluids down for 24 hours in adults, or 8 hours in young children
- Diarrhea in a baby under 6 months, an older adult, a pregnant woman or someone with a weak immune system
- Diarrhea after recent antibiotics or hospital stay
- Diarrhea after travel abroad with fever or blood
Book a routine appointment
- Diarrhea lasting more than 7 days
- Recurrent or persistent diarrhea with weight loss
Usually safe to manage at home
- Vomiting and diarrhea for 1 to 3 days with mild cramps, while drinking enough to pee regularly
Infectious vs noninfectious gastroenteritis
Gastroenteritis means inflammation of the stomach and intestines. It is called infectious when a germ is the cause, and noninfectious when it is caused by something else, such as:
- toxins already made in spoiled food (some forms of food poisoning)
- medicines (NSAIDs, antibiotics, chemotherapy, metformin)
- alcohol
- food allergies and intolerances
- radiation therapy
- chemicals and poisons
Infectious gastroenteritis can spread to other people. Noninfectious forms cannot.
Causes of infectious gastroenteritis
Viruses
| Virus | Typical features |
|---|---|
| Norovirus | Sudden vomiting and diarrhea, all ages, outbreaks in cruise ships, care homes, schools; lasts 1 to 3 days |
| Rotavirus | Young children, watery diarrhea, vomiting and fever for 3 to 8 days; prevented by vaccine |
| Adenovirus 40/41 | Young children, diarrhea lasting up to 2 weeks |
| Astrovirus and sapovirus | Milder illness in children and older adults |
Bacteria
| Bacterium | Usual sources | Features |
|---|---|---|
| Campylobacter | Undercooked poultry, raw milk | Cramps, fever, often bloody diarrhea |
| Salmonella | Eggs, poultry, meat, produce, reptiles | Fever, cramps, diarrhea 6 hours to 6 days after exposure |
| Shigella | Person-to-person, contaminated water | Fever, bloody diarrhea, very contagious |
| Shiga toxin E. coli (O157) | Undercooked beef, raw milk, leafy greens | Bloody diarrhea, little fever, risk of HUS |
| C. difficile | After antibiotics, hospitals | Watery diarrhea, can be severe |
| Vibrio | Raw shellfish | Watery diarrhea |
| Staph aureus and Bacillus cereus toxins | Foods left at room temperature, rice | Vomiting within 1 to 6 hours |
Parasites
- Giardia: from contaminated water, causing greasy, smelly diarrhea, gas and bloating for weeks
- Cryptosporidium: from swimming pools and water, causing watery diarrhea, severe in people with weak immunity
- Entamoeba histolytica: mostly after travel, causing bloody diarrhea
How it spreads
- contaminated food or water
- the fecal-oral route: unwashed hands after using the toilet or changing diapers
- contaminated surfaces (norovirus survives for days)
- airborne particles from vomit (norovirus)
- contact with animals, especially farm animals and reptiles
Symptoms
- diarrhea, watery or bloody
- nausea and vomiting
- cramping belly pain
- fever and chills
- headache and muscle aches
- loss of appetite
Viral vs bacterial gastroenteritis
| Viral | Bacterial | |
|---|---|---|
| Onset | Sudden, vomiting prominent | Diarrhea and cramps prominent |
| Blood in stool | Rare | More common |
| Fever | Low or absent | Often higher |
| Duration | 1 to 3 days usually | 3 to 7 days, sometimes longer |
| Antibiotics | Never helpful | Sometimes helpful |
Diagnosis
Most cases need no tests. Doctors test stool (often with a multiplex PCR panel) when there is:
- bloody diarrhea
- high fever or severe illness
- symptoms lasting more than 7 days
- recent antibiotics or hospitalization
- weakened immunity
- an outbreak investigation or food handler
Blood tests check dehydration and kidney function in more severe cases.
Treatment
Rehydration
- Oral rehydration solution (ORS) in small, frequent sips is the most important treatment
- Babies should continue breastfeeding or formula
- Avoid sugary drinks and undiluted juice, which can worsen diarrhea
- IV fluids for severe dehydration or persistent vomiting
- See dehydration for warning signs
Food
Restart normal eating as soon as you feel able. There is no need for a strict bland diet, though plain foods such as rice, toast, bananas and soup are often easiest at first.
Medicines
- Loperamide can reduce diarrhea in adults with watery diarrhea, but should not be used with bloody diarrhea or high fever, or in young children
- Bismuth subsalicylate may help adults; do not give it to children or teenagers
- Anti-nausea medicine (ondansetron) on prescription
- Antibiotics only for specific infections or situations: severe illness, Shigella, some cases of Campylobacter, travelers' diarrhea that is moderate to severe, C. difficile, and parasites. Antibiotics are avoided in Shiga toxin E. coli infection
Contagious period and returning to work or school
- Norovirus: contagious from the start of symptoms until at least 48 hours after they stop, and virus can be shed for 2 weeks or more
- Bacterial infections: contagious while bacteria are in the stool, which can be weeks
- Stay home until 48 hours after the last episode of vomiting or diarrhea
- Food handlers, healthcare workers and childcare workers may need clearance
Prevention
- wash hands with soap and water, especially after the toilet and before eating; alcohol gels work poorly against norovirus
- clean surfaces with bleach-based cleaners after vomiting or diarrhea
- cook meat, poultry and eggs thoroughly
- avoid raw milk and unpasteurized products
- keep cold foods cold and refrigerate leftovers within 2 hours
- drink safe water when traveling
- rotavirus vaccination for infants
Frequently asked questions
What is infectious gastroenteritis?
It is an infection of the stomach and intestines by viruses, bacteria or parasites that causes diarrhea, vomiting and cramps. Norovirus is the most common cause in adults. It spreads through contaminated food and water, surfaces and close contact.
How do I know if gastroenteritis is viral or bacterial?
Viral gastroenteritis usually starts suddenly with vomiting, causes watery diarrhea and clears in 1 to 3 days. Bacterial gastroenteritis more often causes fever, severe cramps and bloody diarrhea and lasts longer. A stool test confirms the cause when needed.
What is noninfectious gastroenteritis?
It is inflammation of the stomach and intestines not caused by a germ, for example from medicines, alcohol, food intolerance, radiation or toxins. Symptoms can look similar, but it is not contagious.
How long is gastroenteritis contagious?
You are most contagious while you have symptoms and for at least 48 hours afterward. Norovirus can be shed in stool for 2 weeks or more, and some bacteria for several weeks, so careful handwashing continues to matter after recovery.
When do you need antibiotics for gastroenteritis?
Most cases do not need antibiotics. They are used for severe illness, certain bacteria such as Shigella, some travelers' diarrhea, C. difficile and parasites. They are avoided in E. coli O157 infection because they may increase the risk of kidney complications.
Sources
This guide was written from current patient and clinical guidance, including:
- CDC: Norovirus
- CDC: Salmonella
- Infectious Diseases Society of America: 2017 Clinical Practice Guidelines for the Diagnosis and Management of Infectious Diarrhea
- American College of Gastroenterology: Clinical Guideline: Diagnosis, Treatment, and Prevention of Acute Diarrheal Infections in Adults
- World Health Organization: Diarrhoeal disease fact sheet
- NIDDK: Viral Gastroenteritis