Gastroenteritis is a diarrhoea and/or vomiting illness due to an enteric infection.

Gastroenteritis is an acute transient diarrhoeal illness with or without vomiting due to an enteric infection that may be viral, bacterial or parasitic. Common additional symptoms include nausea, fever and abdominal pain.

Worldwide, acute infective diarrhoea is a major cause of mortality, particularly in children under 5 years old. In resource-rich settings (e.g. UK), gastroenteritis is usually a self-limiting illness with symptomatic treatment only.

There are several terms used to describe gastroenteritis illnesses:

  • Diarrhoea: ≥ 3 loose/watery stools per day
  • Acute diarrhoea: diarrhoea that lasts < 14 days
  • Persistent or prolonged diarrhoea: diarrhoea lasting > 14 days
  • Travellers’ diarrhoea: diarrhoea that develops during or within 10 days of returning from a resource-limited country
  • Dysentery: gastroenteritis characterised by diarrhoea with visible blood or mucus. Associated with fever and abdominal pain

Food poisoning is a layman term that is often used synonymously with gastroenteritis. It refers to an illness caused by the consumption of food and/or water that is contaminated by bacteria and/or their toxins, viruses, parasites or chemicals.


Gastroenteritis is estimated to affect 1 in 5 people in the UK each year.

Gastroenteritis is one of the leading causes of death in children under 5 years old in resource-limited countries. Here, it is estimated to account for up to 2 million deaths annually.

In resource-rich countries, gastroenteritis is common, but deaths attributed to gastroenteritis are rare. It is estimated that 10% of children under 5 years old present to healthcare services with gastroenteritis annually. An estimated 20% of the UK population develop symptoms of gastroenteritis each year, but only 1 in 30 present to healthcare services.


Gastroenteritis may be caused by viruses, bacteria or parasites.

The majority of gastroenteritis episodes are self-limiting and caused by viruses. Up to 50% of episodes will last < 24 hours.


Enteric pathogens are transmitted from person-to-person by a number of routes:

  • Faecal-oral route
  • Foodborne
  • Airborne (e.g. vomiting)
  • Environmental (e.g. contaminated surfaces)

Transmission by contaminated food is typically due to enterotoxins, which are toxins produced by microorganisms. This leads to a rapid onset of symptoms following ingestion. Bacteria commonly implicated in gastroenteritis due to enterotoxins are Staphylococcus aureus and Bacillus cereus.


Viruses are commonly implicated in gastroenteritis, particularly in children.

  • Rotavirus
  • Norovirus
  • Adenovirus


A variety of bacteria can lead to gastroenteritis. They may cause a severe watery diarrhoea, similar to viral pathogens, or a bloody diarrhoeal illness (i.e. dysentery). Bacteria are more commonly implicated in bloody (inflammatory) diarrhoea.

  • Watery diarrhoea: due to predominant small bowel involvement. Causes a large volume watery diarrhoea with features of abdominal cramping/bloating and weight loss.
  • Bloody (inflammatory) diarrhoea: due to predominant large bowel involvement. Causes frequent, smaller-volume bloody or mucoid diarrhoea that is associated with fever and severe abdominal pain.

NOTE: bloody diarrhoea with large bowel involvement is referred to as infective colitis.

Certain bacteria may predominantly cause a watery or bloody diarrhoeal illness. However, depending on severity, some can be associated with both and this depends on extent of involvement of the intestines (small and/or large).

Typical causes of watery diarrhoea:

  • Clostridioides (formally Clostridium) difficile
  • Clostridium perfringens
  • Enterotoxigenic Escherichia coli (ETEC)

Typical causes of bloody diarrhoea:

  • Non-typhoidal salmonellosis (e.g. S. typhimurium, S. enteritidis)
  • Campylobacter spp. (e.g. C. jejuni, C. coli)
  • Shigella spp. (S. dysenteriae, S. flexneri, S. boydii, S. sonnei)
  • Yersinia enterocolitica
  • Enterohaemorrhagic Escherichia coli (EHEC)


Parasitic gastroenteritis is commonly associated with foreign travel. Giardia spp. is the most commonly identified pathogen in prolonged travellers' diarrhoea.

  • Cryptosporidium parvum (cryptosporidiosis)
  • Entamoeba histolytica (amoebiasis)
  • Giardia spp. (G. intestinalis, G. lamblia)

Viral gastroenteritis

Rotavirus is the most common cause of gastroenteritis in children.


Rotavirus is a double-stranded RNA virus that commonly causes gastroenteritis in children. It is rare in adults due to long-lasting immunity following infection. Commonly causes a watery diarrhoeal illness with vomiting. Vomiting often settles within 1-3 days and diarrhoea within 7 days.

An oral vaccine against the virus is now part of the childhood immunisation programme.


Norovirus is a single-stranded RNA virus that is the most common cause of gastroenteritis in England and Wales. Infection occurs at all ages and most commonly in the winter months (hence the name ‘winter vomiting bug’). A full recovery usually occur within 2 days.


Campylobacter is the most commonly implicated bacterial cause of gastroenteritis.

Campylobacter is a gram-negative bacillus that is commonly acquired through ingestion of undercooked poultry (and other contaminated food/water). C. jejuni is the most commonly implicated species and causes either a watery or bloody diarrhoeal illness 2-5 days after exposure. The majority of cases are self-limiting within 1 week and 25-50% may be asymptomatic.

Campylobacter gastroenteritis has been linked to the development of several autoimmune conditions following an acute episode (e.g. reactive arthritis, Guillain-Barré syndrome).


Bacillus cereus commonly causes a vomiting illness after reheating starchy food (e.g. rice).

Bacillus cereus is a gram positive rod that produced two enterotoxins:

  • Heat stable emetic toxin (causes vomiting)
  • Heat labile diarrhoeal toxin (causes diarrhoea)

Diarrhoeal illness

Bacillus cereus may contaminate food due to its ability to survive extreme temperatures and form a biofilm. Ingestion of contaminated food with the diarrhoeal enterotoxin leads to a watery diarrhoeal illness 8-16 hours following ingestion with quick resolution (i.e. < 24 hours).

Vomiting illness

Gastroenteritis caused by bacillus cereus is classically described following ingestion of reheated rice (e.g. leaving rice overnight at room temperature with reheating the next day). In this setting, the heat stable enterotoxin is able to survive heating, even if the bacteria themselves are killed. This leads to a rapid onset of vomiting within 1-5 hours of ingestion and resolution within 6-24 hours. Diarrhoea is usually absent because of destruction of the heat labile diarrhoeal enterotoxin during heating.

Bacillus versus staphylococcus

Staphylococcus aureus can also produce an enterotoxin that contaminates food and leads to a rapid-onset gastroenteritis illness. However, the vomiting with S. aureus enterotoxin is usually accompanied with diarrhoea.


Salmonella is commonly acquired through ingestion of contaminated food such as undercooked poultry.

Salmonella typically causes sporadic cases of gastroenteritis, which is transmitted through ingestion of contaminated food (most commonly red and white meat, raw eggs and diary products).

It causes a typical watery diarrhoeal illness, but can be bloody, with associated abdominal pain, fever and vomiting. The illness typically starts within 3 days of exposure and resolves within a week.

Salmonella classification

Salmonella are gram negative bacteria with a rod shape (bacilli). Salmonella is the genus, which is further divided into two species: enterica and bongori.

Salmonella enterica is divided into six subspecies. The majority of human pathogens belong the to subspecies enterica. The full name being salmonella enterica subsp. enterica. This subspecies is divided into many different serotypes, which is a way of classifying microorganisms based on their cell surface antigens. Including all the subspecies, there are >2600 different salmonella serotypes.

Important serotypes of salmonella enterica subsp. enterica include:

  • Salmonella enteritidis: cause of gastroenteritis
  • Salmonella typhimurium: cause of gastroenteritis
  • Salmonella typhi: cause of typhoid fever
  • Salmonella paratyphi: cause of paratyphoid fever

Non-typhoidal salmonellosis

Gastroenteritis due to salmonella is usually the result of the non-typhoidal serotypes S. enteritidis and S. typhimurium. They are one of the major causes of acute diarrhoea in resource-rich countries.


Shigella is a classic cause of dysentery in young children.

Shigella spp. cause a classic dysentery type illness (i.e. bloody/mucoid diarrhoea associated with fever and abdominal pain) that commonly affects young children (< 5 years old). It is most common in late summer and spread by direct human-to-human transmission because the bacteria only colonises humans and some nonhuman primates.

The illness usually begins 1-3 days following exposure and resolves within 7 days.

Escherichia coli

Different types of Escherichia coli can cause gastroenteritis.

Escherichia coli (E. coli) is a single species of the genus Escherichia. This species is further divided into different groups based on their genomic relatedness. Within each group are individual strains, which are given a sequence of numbers and letters (e.g. O157).

There are different intestinal pathogenic strains of E. coli, which can include:

  • Enterohaemorrhagic E. coli (EHEC): also known as Shigatoxigenic Escherichia coli (STEC) because it produces a Shiga-toxin.
  • Enterotoxigenic E. coli (ETEC)
  • Enteropathogenic E. coli (EPEC)

Within each of the these strains are different serotypes. Serotypes are differentiated based on their cell surface antigens.


There are many serotypes of EHEC, which classically cause a bloody diarrhoeal illness. In the UK, E. coli O157 is the most common serotype of EHEC that commonly infects children < 5 years old.

Infection may be asymptomatic or cause a diarrhoeal illness (classically dysentery-type illness), which begins within 3-4 days of exposure and resolves within 10 days. It is most commonly transmitted by contaminated food (e.g. meat, salad, water) but is also seen from direct human-to-human spread, which can be due to contact with infected animals (e.g. petting zoos).

Infection with the EHEC O157 can cause haemolytic uraemic syndrome (HUS) in up to 20% of infected children and accounts for 90% of cases of HUS in children. HUS is characterised by microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury. Treatment is usually supportive.


Commonly associated with a watery diarrhoeal illness in travellers or resource-limited countries.


The majority of cases of Entamoeba histolytica are asymptomatic.

Entamoeba histolytica is an anaerobic parasite that is highly prevalent worldwide. In countries like the UK, E. histolytica is usually acquired among travellers returning from endemic areas. The majority of cases are asymptomatic (~90%) and those who develop symptoms usually have a subacute onset over weeks.

The presentation ranges from mild diarrhoeal illness to severe dysentery.


Giardia lamblia is commonly implicated in Travellers’ diarrhoea.

Giardia lamblia is spread by a variety of routes and leads to a classic watery diarrhoea alongside symptoms of abdominal pain, anorexia, flatulence and bloating. It is commonly implicated in travellers’ diarrhoea and the most commonly isolated organism in prolonged Travellers’ diarrhoea (> 14 days).

Overtime, if G. lamblia remains untreated it may lead to malabsorption and weight loss.

Clinical features

Gastroenteritis is characterised by an acute onset of diarrhoea with or without vomiting.

Gastroenteritis may cause a mild self-limiting illness. In some cases it can be severe leading to profound dehydration and shock requiring inpatient admission.

History taking

There may be a history of contaminated food intake (e.g. take away chicken). Must consider the following:

  • Food & drink: Recent food intake, exposure to contaminated water
  • Foreign travel
  • Contacts: exposure to any unwell individuals or known outbreaks (e.g. care home)
  • Occupation
  • Co-morbidities: risk of immunosuppression (e.g. medications, HIV), recent antibiotic use (at risk of C. diff colitis)


  • Diarrhoea: may be described as watery, bloody or mucoid
  • Nausea & vomiting
  • Fever
  • Abdominal pain
  • General malaise
  • Bloating/cramping
  • Weight loss


  • Features of dehydration: poor capillary refill time, dry mucous membranes, poor feeding, irritable, poor urine output, altered mental status
  • Features of shock: tachycardia, hypotension
  • Abdominal pain

Assessing dehydration

It is important to assess for signs of dehydration and shock.

Gastroenteritis can cause a severe diarrhoeal illness leading to significant fluid loss, electrolyte derangement and marked dehydration. It is important to assess for dehydration and shock in both adults and children.


The features of dehydration in adults may be broadly divided into mild, moderate and severe.

  • Mild: malaise, anorexia, nausea, postural hypotension
  • Moderate: mild features + tiredness, dizziness, headache, muscle cramps, dry mucous membranes, sunken eyes, reduced skin elasticity, prolonged capillary refill time, tachycardia, oliguria
  • Severe: mild and moderate features + marked weakness, confusion, alter mental status, hypotension, anuria


The NICE clinical guidelines CG84 has an excellent summary on the signs and symptoms of dehydration and shock in children.

Diagnosis & investigations

Stool cultures are used to help confirm a clinical diagnosis of gastroenteritis, but not always required.

Gastroenteritis is normally a clinical diagnosis based on a typical history of acute onset diarrhoea with or without vomiting. Stool cultures including MC&S, virology, C. diff +/- Ova, cysts and parasites (OCP) can be helpful to confirm the diagnosis, but this is not needed in all cases and a negative test does not exclude the diagnosis.

Stool cultures

Stool cultures include MC&S, virology, C. Diff +/- OCP. They are not required in all patients.

  • MC&S: basic stool sample that is able to look for commonly implicated bacteria. Can be isolated through culture or use of polymerase chain reaction. This latter method amplifies bacterial genetic material.
  • Virology: may be utilised to identify culture-negative gastroenteritis. Assesses common viruses (e.g. rotavirus, norovirus).
  • C. diff: different methods are available including PCR-based or immunoassay-based. For more information see Clostridium difficile notes.
  • OCP: used to detect parasitic organisms. Usually only performed in Travellers’ diarrhoea or significant travel history

Stool cultures may be requested in the following circumstances

  • Systemically unwell patient
  • High-risk patient (e.g. elderly, pregnant, immunosuppressed)
  • Dysentery illness (more likely to be a bacterial pathogen)
  • Recent antibiotic use (particularly looking for C. difficile)
  • Prolonged diarrhoea
  • Suspected food poisoning
  • Foreign travel

Blood tests

Blood tests are not routinely required in patients with gastroenteritis unless the patient appears unwell or significant dehydration is suspected. They are useful to assess for complications (e.g. acute kidney injury, HUS). but do not help discriminate between causes of gastroenteritis.

  • Full blood count
  • Urea & electrolytes
  • Bone profile (at risk of hypomagnesaemia)
  • C-reactive protein
  • Venous blood gas (performed in A&E in any unwell patient)
  • Blood cultures: if febrile or evidence of sepsis


Imaging is not routinely recommended in patients with gastroenteritis.

X-rays (XR) or computed tomography (CT) may be requested in patients with severe symptoms (e.g. peritonitis, severe pain, signs of obstruction) to exclude a more sinister pathology (e.g. diverticulitis, obstruction, perforation). Typical features on imaging are intestinal wall thickening with surrounding inflammatory changes.

Management - adults

The mainstay of treatment in adults is supportive care.

In most cases, gastroenteritis is a self-limiting illness that improves with supportive treatment alone. This means maintaining good oral intake to prevent dehydration, rest and good basic hygiene to prevent transmission.

Hospital admission

The majority of adults can be managed with simple measures at home. However, there are situations when it is appropriate to advise hospital admission for inpatient treatment. These include:

  • Systemically unwell, features of severe dehydration and/or shock
  • Persistent/intractable vomiting or high-output diarrhoea
  • Suspected sepsis
  • Failure to respond to oral rehydration, unable to take oral intake or unable to be cared for at home
  • Consider if major co-morbidities (e.g. frail and elderly, immunosuppressed, concurrent illness): higher risk deterioration


In the first instance, rehydration with oral fluid is the most important management of gastroenteritis. A significant amount of fluid can be lost through diarrhoea and vomiting.

Outpatient (low-risk patients)

In otherwise healthy adults, a simple increase in fluid intake is usually all that is required to prevent dehydration. This can be supplemented with fruit juices and soups to meet fluid and electrolyte needs. In more severe cases, oral dehydration solution (ORS) can be used as a supplemental fluid.

A common over the counter ORS is Dioralyte. Dioralyte is potassium chloride with rice powder, sodium chloride and sodium citrate. One sachet can be reconstituted in 200 mL of water. Approximately 200-400 mL of the reconstituted liquid should be advised after every loose motion, but more if more extensive fluid loss.

Inpatient (high-risk patients)

Patients requiring inpatient admission for gastroenteritis can be treated with intravenous fluids. The amount of fluid depends on the extent of dehydration and/or shock and depends on the patients' co-morbidities. Ensure you replace electrolytes as needed.

For more information on fluid management in adults see the NICE clinical guideline CG174.


Antibiotics are not routinely needed in patients with gastroenteritis.

Antibiotics may be indicated if a specific organism is identified on stool cultures, among high-risk patients, or among patients with severe or prolonged symptoms. It is usually advisable to liaise with microbiology.

NOTE: the use of quinolones (e.g. ciprofloxacin) in patients with gastroenteritis secondary to Shigella spp. or EHEC O157 is associated with an increased risk of HUS.

Anti-diarrhoeal agents

Loperamide is a common anti-diarrhoeal medication that can be bought over the counter. Loperamide binds to gut opioid receptors leading to reduced intestinal motility. Loperamide is not routinely recommended.

They may be purchased by patients with mild-to-moderate symptoms of gastroenteritis for symptom relief. However, it should be advised to avoid if patients have any features of dysentery or confirmed Shigella spp. or EHEC. In these cases, there is a risk of toxic colonic dilatation.

Management - children

Treatment in children is usually supportive, but it is important to assess for signs of dehydration and shock.

The management of children with gastroenteritis is very similar to adults. The majority of children will have a self-limiting illness that dose not require any specific treatment other than rehydration and supportive care.

Hospital admission

Children with gastroenteritis may require inpatient admission in the following circumstances:

  • Severe dehydration and/or shock
  • Persistent/intractable bilious vomiting
  • Acute-onset bloody diarrhoea
  • Suspected sepsis, HUS or confirmed EHEC O157 infection
  • Failure to respond to oral rehydration, unable to take oral intake or unable to be cared for at home
  • Red flags features (see ‘assessing dehydration’).


The principle treatment of children with gastroenteritis is rehydration, which is preferably by the oral route. A low-osmolarity ORS can be used to rehydrate children (e.g. dioralyte). Rehydration in children is dependent on the child’s weight that is used to calculate their daily maintenance fluid, degree of dehydration and ability to take oral intake/breastfeed.

Daily maintenance fluid requirement

A child’s total daily fluid requirement (i.e. maintenance fluid) should be determined based on weight.

  • Weight 0-10 kg: 100 mL/kg/day
  • Weight 10-20 kg: 1000 mL/day + 50 mL/kg for each kg over 10 kg per day
  • Weight >20 kg: 1500 mL/day + 20 mL/kg for each kg over 20 kg per day

Advice on fluid rehydration

  • Age (< 5 years old): give 50 ml/kg of ORS solution for rehydration over 4 hours plus maintenance volume required by the child for that 4-hour period of time.
  • Age (5-11 years old): give 200 mL ORS after each loose stool in addition to normal maintenance fluid.
  • Age (12-16 years old): give 200-400 mL ORS after each loose stool

Any child with ongoing risk of dehydration should receive 5 mL/kg of ORS after each large watery stool.

For more information of fluid management in children see the NICE clinical guideline NG29 and CG84.


Antibiotics are not routinely needed in children with gastroenteritis. The majority of cases are viral and self-limiting. Antibiotics may be suggested if a specific bacteria is isolated on stool culture.

Anti-diarrhoeal agents

Use of anti-diarrhoeal agents is not recommended in children with gastroenteritis.

Notifiable diseases

Gastroenteritis may be caused by notifiable microorganisms that should be reported to the local health protection team.

Notifiable diseases

The following diseases may be seen in patients with a clinical diagnosis of gastroenteritis and should be reported.

  • Cholera
  • Food poisoning
  • Infectious bloody diarrhoea
  • HUS
  • Enteric fever (typhoid or paratyphoid fever)

Notifiable microorganisms

The following microorganisms can cause gastroenteritis and should be reported if identified.

  • Bacillus cereus (if due to food poisoning)
  • Campylobacter spp
  • Clostridium perfringens (if due to food poisoning)
  • Cryptosporidium spp
  • Entamoeba histolytica
  • Giardia lamblia
  • Salmonella spp
  • Shigella spp


Complications are more likely to occur in high-risk patients (infants, young children, pregnancy, elderly, co-morbid).

A variety of complications may occur during or following gastroenteritis, which is dependent on both the patient and organism involved. Here we list some of the more pertinent complications to recognise:

  • Dehydration and/or shock
  • Acute kidney injury
  • HUS: seen in 10% of EHEC O157 cases. Characterised by microangiopathic haemolytic anaemia, thrombocytopaenia and acute kidney injury. Increased risk of chronic kidney disease and mortality of 3-5%. Most commonly affects young children.
  • Sepsis: seen with invasive organisms
  • Inflammatory diseases: reactive arthritis, Guillain-Barré syndrome. Particularly with Campylobacter spp
  • Post-infectious irritable bowel syndrome (IBS)
  • Toxic megacolon: toxic dilatation of the colon, which can lead to perforation

Post-infectious IBS

This refers to the development of IBS following an episode of gastroenteritis. This is seen in approximately 10% of patients after gastroenteritis. A formal diagnosis is made by the development of IBS symptoms after resolution of acute gastroenteritis. Gastroenteritis in this setting is defined by a positive stool culture in a symptomatic patient or presence of two characteristic features (e.g. fever and/or vomiting and/or diarrhoea). Risk factors for the development of post-infectious IBS include female sex, young age, prolonged fever, anxiety and depression.

For more information, see irritable bowel syndrome notes.

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