Gastroenteritis is the general term used to describe inflammation of the gastrointestinal tract, usually considered infective in origin (although it may have non-infective causes).

It is a transient disorder and refers to a combination of symptoms such as diarrhoea, vomiting, and abdominal pain, although not all have to be present in order to make the diagnosis. The most common cause is viral, contributing to 30-40% of gastroenteritis in developed countries.

Importantly, subtle differences in the length of time between ingestion of food and development of symptoms can often reveal the causative agent (bacterial toxins – hours, viruses – days, bacteria – weeks, parasites –  months).

Clarification of Terminology

  • Diarrhoea: 3 or more loose stools or stools with increased liquid per day (as defined by the WHO)
  • Acute diarrhoea: Lasting less than 14 days
  • Chronic diarrhoea: Lasting more than 14 days
  • Dysentery: gastroenteritis characterised by loose stools with blood and mucus
  • Travellers’ diarrhoea: More than 3 loose stools commencing within 24 hours of foreign travel, with or without cramps, nausea, fever or vomiting (most common cause is Enterotoxigenic E. Coli (ETEC))
    • Patient’s travelling to at risk areas may be required to take prophylactic anti-microbials

Risk Factors

  • Poor food preparation, handling and cooking
  • Immunosuppression
  • Poor personal hygiene

Clinical Features

Patients will typically present with a cramp-like abdominal pain and diarrhoea (with or without blood or mucus). There may be associated vomiting, pyrexia, night sweats, and weight loss reported. On examination, a patient will be dehydrated (of varying degrees of severity) with possible pyrexia and / or hypovolaemia.

Specific features from the history to note for any suspected cases of infective gastroenteritis include:

  • Bowel movements – quantity and character (blood stained, mucus, profusely watery)
  • Affected family or friends
  • Recent travel
  • Recent use of antibiotics within the previous four weeks
    • Can suggest potential C. difficile infection (discussed below)

if necessary, it may be relevant to ask the patient about features for specific complications of certain causative organisms (as discussed below), such as Guillain Barre syndrome, reactive arthritis, or haemolytic uraemic syndrome.


Investigations are not necessary for most cases as the condition is usually self-limiting. However, a stool culture is required (inc C. diff and norovirus if the history lends itself), especially if there is blood or mucus in the stool, if the patient is immunocompromised, or if severe or persistent.


The general points of management for any patient with gastroenteritis includes:

  • Rehydration, encouraging oral fluid intake where possible
    • If severe dehydration or unable to tolerate oral fluid, consider admitting the patient for IV fluids*
  • Education to prevent future episodes.
  • Exclusion from work is usually 48 hours from the last episode of vomiting or diarrhoea.

In the UK, both food poisoning and infectious bloody diarrhoea are notifiable diseases and it is the duty of the diagnosing doctor to notify the appropriate body. Certain organisms are also notifiable (Campylobacter and Salmonella), however this is the duty of the laboratory to notify the Public Health body regarding this.

*Ensure suitable potassium replacement if severe or persistent vomiting or diarrhoea

Infective Causes


Norovirus: This is a RNA virus. It is the most common form of viral gastroenteritis in adults and presents with abdominal cramps, watery diarrhoea, and vomiting. It usually lasts about 1-3 days and is often a course of institutional infection.

Fig 2 - Rotavirus particles. Rotavirus is a common cause of diarrhoea in the young.

Figure 1 – Rotavirus particles. Rotavirus is a common cause of diarrhoea in the young.

Rotavirus: This is a double stranded RNA virus. It is the most common cause of severe diarrhoea among infants and young children and generally lasts less than a week. Infection in childhood generates life long immunity.

Adenovirus: This is a DNA virus. Another common cause of diarrhoea in children.


Campylobacter: A Gram negative bacillus (commonly C. jejuni or C. coli).  The most common cause* of food poisoning and typically results from the ingestion of chicken, eggs or milk. There may be a prodrome of fatigue, fever and myalgia followed by nausea, abdominal cramps, and diarrhoea. If severe, treat with IV erythromycin. 

E. Coli: A Gram negative bacillus. It is typically transmitted through contaminated foodstuffs but also from infected animals and from person to person contact. Several forms of the bacteria exist, but Enterohaemorrhagic E. coli (EHEC)** is the most common cause of Travellers’ diarrhoea

Salmonella: A Gram negative flagellated bacillus (two serotypes most commonly associated with gastroenteritis, S. typhimurium and S. enteritidis). It is transmitted through undercooked poultry or raw eggs, causing fever, nausea, vomiting, abdominal cramps and bloody diarrhoea. Management is generally conservative and infection generally lasts <7 days.

Shigella: A Gram negative bacillus (S sonnei is most common serotype). It is acquired from contaminated dairy products and water, presenting with fever, abdominal pain, rectal pain, or bloody diarrhoea. Management is generally conservative.

*Campylobacter infections can also result in reactive arthritis, Guillan Barre syndrome, haemolytic uraemic syndrome, and thrombotic thrombocytopaenic purpura

**A complication of EHEC is haemorragic uraemic syndrome (especially from serotype E. coli 0157:H7).

Fig 2 - Scanning electron micrograph image of Campylobacter jejuni, showing its characteristic spiral shape.

Figure 2 – Scanning electron micrograph image of Campylobacter jejuni, showing its characteristic spiral shape.

Bacterial Toxins

Toxins from bacteria often cause an acute onset of diarrhoea and vomiting and symptoms tend to last less than 24 hours.

  • Staphylococcus Aureus: Typically found in cooked meat and cream products, even re-heating of the cooked food does not destroy the exotoxin (even if the bacteria are destroyed).
  • Bacillus Cereus: This is typically acquired through reheated rice and causes rapid-onset nausea and vomiting.
  • Clostridium Perfringes: This is typically acquired from re-heating meat dishes and causes diarrhoea yet vomiting is unusual.
  • Vibrio Cholera: This is typically acquired from contaminated water supplies and causes profound watery diarrhoea, often described as rice water, yet painless in nature. An oral vaccine is available.


In any patient with Travellers’ diarrhoea, parasites are much more likely to be the causative organism

Cryptosporidium:  This is a protozoan which can cause a self-limiting watery diarrhoea with abdominal cramps in most patients. However in those who are immunocompromised, such infections may be life threatening. Diagnosis involves stool culture for ova, cysts and parasites.

Entamoeba Histolytica: This organism is responsible for amoebiasis. It is acquired from the ingestion of food or water contaminated with faeces, presenting with symptoms of bloody diarrhoea, abdominal pain, and fever. An amoebic liver abscess can also occur, which presents with right upper quadrant pain, a swinging pyrexia, and hepatomegaly. Stool culture for ova, cysts and parasites is required and recommended treatment is metronidazole or tinidazole.

Giardia intestinalis: This organism is responsible for giardiasis. Transmitted through direct contact or faeco-oral route, it can cause acute disease (explosive diarrhoea, fever, fatigue, nausea and bloating) or chronic disease (steatorrhea, malabsorption and weight loss). Stool culture for ova, cysts and parasites may show trophozoites (‘tear drop’ shaped on microscopy) and duodenal biopsy can reveal villous atrophy. Management advised is usually metronidazole or tinidazole.

Schistosoma: This organism causes schistosomiasis. Acquired from contaminated water, acute schistosomiasis develops about a month after the initial infection, presenting with fever, malaise, abdominal pain, bloody diarrhoea, and hepatosplenomegaly (which can develop into chronic liver disease and portal hypertension). Eosinophilia may be seen on full blood count and a stool culture for ova, cysts and parasites is required. It is treated with praziquantel.

Fig 3 - The life cycle of entamoeba histolytica.

Figure 3 – The life cycle of entamoeba histolytica.

Hospital-Acquired Gastroenteritis

The major species for hospital acquired gastroenteritis is C. difficile. It is a Gram positive organism and typically develops following treatment with broad-spectrum antibiotics (particularly cephalosporins), disrupting the normal microbiota of the bowel.

The bacteria produce exotoxins A & B, causing an inflammatory response in the bowel that results in an inflammatory exudate on the colonic mucosa with intervening areas of normal mucosa, This culminates in severe bloody diarrhoea, which has the potential to develop into toxic megacolon (severely dilated bowel with high risk of perforation).

Investigation requires stool culture specifically including C. difficile Toxin (CDT); results may report the presence of the bacteria but not of the toxin, in such cases these reports should be interpreted relative to the clinical picture. Treatment requires IV fluid rehydration and oral metronidazole; vancomycin can be started in severe disease or if no improvement is seen after 72 hours.

Fig 4 - Abdominal X-Ray of toxic megacolon

Fig 4 – Abdominal X-Ray of toxic megacolon

Non-Infective Causes

Non-infective causes of gastroenteritis include:

  • Radiation colitis – inflammation of the gastroentestinal tract secondary to radiation therapy.
  • Inflammatory bowel disease.
  • Microscopic colitis (a cause of chronic watery diarrhoea which typically affects middle-aged females. The colon is macroscopically normal on endoscopy however biopsy demonstrates an increase in the number of inflammatory cells.
  • Chronic ischaemic colitis – caused by a compromise in blood supply to the colon. It commonly affects the watershed area around the splenic flexure. Diagnosis is confirmed by endoscopy where one might observe ‘blue swollen mucosa’.

Key Points

  • Gastroenteritis is a common condition and is caused by a variety of organisms, including viruses, bacteria, bacterial toxins, and parasites
  • Important causes of dysentery include campylobacter, shigella, salmonella, and norovirus
  • If the patient has travelled abroad, think parasites.
  • Have a low threshold for treatment in immunocompromised patients.

Appendix 1 – Summary Table

  • Most common cause of adult gastroenteritis
  • RNA virus
  • Presents with watery diarrhoea, abdominal pain and vomiting
  • RNA type virus
  • Most common cause of severe diarrhoea in young children
  • Lifelong immunity once exposed
  • DNA virus
  • Most common causative organism in food poisoning
  • Gram-negative bacillus
  • May present with prodrome of fatigue, fever and myalgia followed by diarrhoea and abdominal pain
  • Associated with Reactive Arthritis and Guillen-Barre Syndrome
Escherichia Coli
  • Most common causative organism of traveller’s diarrhoea, spread by faeco-oral transmission
  • Gram-negative bacillus
  • E Coli serotype O157:H7 is prone to cause Haemorrhagic Uraemic Syndrome
  • Two most common serotypes for gastroenteritis are S. Typhimurium and S. Enteritidis
  • Gram negative flagellated bacillus
  • Acquired from contaminated dairy products and water
  • Gram negative bacillus
Bacterial Toxins
  • Staphylococcus Aureus – Found in poorly controlled meat or cream products, even re-heating affected cooked food does not destroy the exotoxin
  • Bacillus Cereus – Acquired through reheated rice and causes rapid-onset diarrhoea and vomiting
  • Clostridium Perfringes: Acquired from re-heating meat dishes and causes mainly diarrhoea
  •  A protozoa, with diagnosis made by stool culture (for ova, cysts and parasites)
  • Causes a self-limiting watery diarrhoea
Entameoba histiolytica
  • Typically causes bloody diarrhoea with fever, yet can cause amoebic liver abscess (presenting as swinging pyrexia and RUQ pain)
  • The main organism responsible for amoebiasis. A stool culture is required for diagnosis
  • Can present acutely or chronically:
    • Acute –  severe diarrhoea, fever, nausea and bloating
    • Chronic – steatorrhoea, malabsorption, and weight loss
  • A stool culture is needed for diagnosis (for ova, cysts and parasites, as well as possible trophozoites (‘tear drop shaped’); a duodenal biopsy can show villous atrophy
  • Acquired from contaminated water, with an African snail being the vector
  • 1 month post-ingestion can present as fever, abdominal pain, bloody diarrhoea and hepatosplenomegaly; chronically can develop into chronic liver disease and portal hypertension
  • Eosinophilia may be seen on FBC and a stool culture for ova, cysts and parasites is required

Further Reading

Escherichia coli O157
Pennington H, The Lancet

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