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Original Author(s): Sittiga Hassan
Last updated: October 25, 2019
Revisions: 37

Original Author(s): Sittiga Hassan
Last updated: October 25, 2019
Revisions: 37

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Gastroenteritis is the term used to describe inflammation of the gastrointestinal tract, usually considered infective in origin (although often non-infective).

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)

Risk Factors

  • Poor food preparation, handling and cooking
  • Immunocompromise
  • 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, the patient will often be dehydrated (of varying  severity) with potential pyrexia.

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

  • Bowel movements (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)

In rarer cases, patients may present with specific complications of certain causative organisms, 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 often warranted, especially if cases with 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 include:

  • 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.

Infective Causes


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

  • 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.
  • 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. The most common cause* of food poisoning and typically results from the ingestion of affected chicken, eggs, or milk. There may be a prodrome of fatigue, fever, or myalgia followed by nausea, abdominal cramps, and diarrhoea.
    • Campylobacter infections can also result in reactive arthritis, Guillan Barre syndrome, haemolytic uraemic syndrome, and thrombotic thrombocytopaenic purpura
  • E. Coli: A Gram negative bacillus. 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
    • E. coli serotype 0157:H7 is associated with causing haemorragic uraemic syndrome
  • 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.
  • Shigella: A Gram negative bacillus (S. sonnei being the most common serotype). It is acquired from contaminated dairy products and water, presenting with fever, abdominal pain, rectal pain, or bloody diarrhoea
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. Common bacterial toxins include:

  • 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
    • Notably, an oral vaccine is available


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

Figure 3 – The life cycle of entamoeba histolytica

  • Cryptosporidium:  This is a protozoan which typically causes a self-limiting watery diarrhoea with abdominal cramps (however may be life threatening in those who are immunocompromised). 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. Stool culture for ova, cysts and parasites is required and recommended treatment is metronidazole or tinidazole.
    • An amoebic liver abscess can also occur, which presents with right upper quadrant pain, pyrexia, and hepatomegaly
  • Giardia intestinalis: This organism is responsible for giardiasis. Transmitted through direct contact or faeco-oral route, it can cause acute disease (diarrhoea, fever, fatigue, nausea, and bloating) or chronic disease (steatorrhoea, 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.

Hospital-Acquired Gastroenteritis

Figure 4 – Abdominal radiograph of toxic megacolon

The main pathogen for hospital acquired gastroenteritis is C. difficile. It is a Gram positive organism and typically develops following 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 requiresstool 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.

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 condition where the colon is macroscopically normal on endoscopy however biopsy demonstrates an increase in the number of inflammatory cells presenr
  • Chronic ischaemic colitis – caused by a compromise in blood supply to the colon, most commonly affecting the watershed area around the splenic flexure. Diagnosis is confirmed by endoscopy where one might observe ‘blue swollen mucosa’

Key Points

  • Gastroenteritis 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, ensure to consider parasites in the differentials
  • Have a low threshold for treatment in immunocompromised patients