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Last updated: July 14, 2020
Revisions: 39

Last updated: July 14, 2020
Revisions: 39

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

They are most often transient, presenting with 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; as a general rule: 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

Risk Factors

  • Poor food preparation, especially in handling and cooking
  • Immunocompromised
  • 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, 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 abroad
  • Recent use of antibiotics within the previous four weeks
    • Can suggest potential C. difficile infection (discussed below)

In rare 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 in 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, the patient may need admission for intravenous fluid rehydration
  • 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 identifying the organism to notify the Public Health body about this.

Infective Causes


  • Norovirus – single-stranded RNA virus (Fig. 1), the most common form of viral gastroenteritis in adults, presents with abdominal cramps, watery diarrhoea, and vomiting, usually lasting 1-3 days
  • Rotavirus – double-stranded RNA virus, results in a severe diarrhoea among infants and young children, generally self-resolves in less than a week
  • Adenovirus – double-stranded DNA virus, also a common cause of diarrhoea in children

Figure 1 – Rotavirus particles, as seen on electron microscopy


  • Campylobacter – Gram negative bacillus (Fig. 2), the most common cause of food poisoning (typically from ingestion of affected chicken, eggs, or milk), can have 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 – Gram negative bacillus, typically transmitted through contaminated foodstuffs (but can also spread from animals to human or from person to person contact); several forms of the bacteria exist, but Enterotoxigenic E. coli (ETEC) is the most common cause of Travellers’ diarrhoea
    • E. coli serotype 0157:H7 is associated with causing haemorragic uraemic syndrome
  • Salmonella – Gram negative flagellated bacillus (two serotypes most commonly associated with gastroenteritis, S. typhimurium and S. enteritidis), transmitted through undercooked poultry or raw eggs; results in fever, vomiting, abdominal cramps, and bloody diarrhoea
  • Shigella – Gram negative bacillus, commonly acquired from contaminated dairy products and water; presents with fever, abdominal pain, or bloody diarrhoea

Figure 2 – Electron microscopy 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 can arise from:

  • Staphylococcus aureus – typically found in meat or dairy products, even re-heating of the cooked food does not destroy the exotoxin (even if the bacteria are destroyed)
  • Bacillus cereus – usually found in reheated rice, known to cause rapid-onset vomiting and abdominal cramps
  • Clostridium perfringes – typically acquired from re-heating meat dishes; causes diarrhoea yet vomiting is less common
  • Vibrio cholera – acquired most commonly from contaminated water supplies and causes profound watery painless diarrhoea; an oral vaccine is available


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

  • Cryptosporidium – protozoan that typically causes a self-limiting watery diarrhoea and abdominal cramps (can be life-threatening in those who are immunocompromised); diagnosis is made with stool culture for ova, cysts, and parasites.
  • Entamoeba histolytica – anaerobic amoebozoan that becomes acquired from the ingestion of food or water contaminated with faeces (Fig. 3), presents with bloody diarrhoea, abdominal pain, and fever (can also result in liver abscess); stool culture for ova, cysts and parasites is required for diagnosis, recommended treatment is metronidazole or tinidazole
  • Giardia intestinalis – parasite transmitted through direct contact or faeco-oral route, can cause either acute disease (diarrhoea, fever, fatigue, nausea, and bloating) or chronic disease (steatorrhoea, malabsorption, and weight loss); diagnosis made with stool culture for ova, cysts and parasites, recommended treatment is metronidazole or tinidazole
  • Schistosoma – a fluke, acquired through contaminated water, with acute schistosomiasis developing about a month after the initial infection, presenting with fever, malaise, abdominal pain, bloody diarrhoea, and severe cases even leading to chronic liver disease; eosinophilia may be seen on full blood count and a stool culture for ova, cysts and parasites is required, with treatment via praziquantel

Figure 3 – The life cycle of entamoeba histolytica

Hospital-Acquired Gastroenteritis

The main pathogen for hospital acquired gastroenteritis is C. difficile, a Gram positive organism that can develop following the use of broad-spectrum antibiotics, disrupting the normal microbiota of the bowel. This allows the excess overgrowth of the C. difficile bacteria, leading to the organism being able to also produce large amounts of exotoxins A & B

The exotoxins produce a sizeable immune response from the bowel, resulting in inflammatory exudate on the colonic mucosa (with intervening areas of normal mucosa). This presents clinically with severe bloody diarrhoea, and has the potential to develop into toxic megacolon (severely dilated bowel with high risk of perforation, Fig. 4) if left untreated.

Investigation requires both stool culture and C. difficile Toxin (CDT) testing*. Treatment requires intravenous fluid rehydration and oral metronidazole; vancomycin can be started in severe disease or if no improvement is seen after 72 hours.

*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

Figure 4 – Abdominal radiograph of toxic megacolon

Non-Infective Causes

Non-infective causes of gastroenteritis include:

  • Radiation colitis – inflammation of the gastrointestinal tract secondary to radiation therapy
  • Inflammatory bowel disease, such as Crohn’s Disease or Ulcerative Colitis
  • Microscopic colitis – a condition where the colon is macroscopically normal on endoscopy however biopsy demonstrates an increase in the number of inflammatory cells present
  • 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