Infective Gastroenteritis


  • Around 20% of the UK population develop infectious gastroenteritis a year.
  • Transient disorder caused by enteric infection with viruses, bacteria or protozoa, characterised by sudden onset diarrhoea, with or without vomiting.
  • Commonly viral (~40%). NB The causative organism is not identified in the majority of patients.
  • Major cause of morbidity/mortality worldwide


  • Short (<6 hours) incubation – suggests toxin-producing organisms
    • Staph aureus
      • Transferred from hands of food handlers to dairy products and cooked meats.  Organism can remain/grow if food is not properly stored
      • Most common symptoms are nausea/profuse vomiting (diarrhoea less severe).  Often also accompanied by a marked leucocytosis (can be misleading; due to enterotoxin acting as a superantigen)
    • Bacillus cereus
      • Commonly found in fried rice and fresh sauces
      • Ingestion of preformed heat-stable exotoxin causes rapid onset vomiting (minor diarrhoea) which resolves within 24 hours.  If viable organism ingested, the incubation period can be longer and watery diarrhoea and cramps are more common (also self-limiting)
    • Clostridium perfringes
      • Commonly transmitted from poorly cooked meat and classically occurs as point source outbreaks e.g. group of people all ate at the same canteen.
      • Ingestion of the toxin produces symptoms of diarrhoea and cramps within 6-12 hours.  Illness is usually self-limiting.
  • Longer incubations (12-72 hours)
    • Campylobacter jejuni
      • Most common cause of gastroenteritis in the UK
      • Most common sources are chicken, beef and contaminated milk products.
      • Incubation period 2-5 days.
      • Symptoms are usually colickly abdominal pain (can be severe) with nausea, vomiting and significant diarrhoea which may be bloody
        • Usually lasts 5-7 days
    • Salmonella spp
      • Now rarer in the UK.  Most common strain causing gastroenteritis is S enteritidis.  More common in the elderly (due to achlorydia) and paediatric populations
      • Source is usually from animal sources (faecal contamination) e.g. beef, poultry, unpasteurised milk products
        • Can be contagious via humans (faecal-oral)
      • Incubation period is usually 12-72 hours and the main symptom is diarrhoea (occasionally bloody)
        • Occasionally, in severe cases, patients can become bacteraemic and require antibiotic treatment
        • Reactive arthritis in 2%
    • Escherichia coli
      • There are at least 5 different strains with slightly different features:
        • Enterotoxigenic E coli (ETEC)
          • Cause the majority of cases of traveller’s diarrhoea
          • Incubation period of 12-48 hours and usually self-limiting after 3-4 days of symptoms (weeks would suggest another organism)
          • Secretory (loose) diarrhoea predominates as a result of toxin production
        • Entero-invasive E coli (EIEC)
          • Similar to Shigella dysentery and caused by invasion and destruction of enterocytes
          • Watery diarrhoea (occasionally some blood) and abdominal cramps are common and rarely are severe. Self limiting.
        • Enteropathogenic E coli (EPEC)
        • Enterohaemorrhagic E coli (E coli ‘O-types’; or verotoxin producing E coli- VTEC)
          • Possess genes necessary for adherence (as do EPEC) and ability to produce verotoxins (these are ‘shiga’ toxins- identical to that produced by Shigella)
          • Usually from poorly cooked/prepared meats (originate from herbivores gut flora) but many other sources have been implicated
            • <100 organisms required to infect (very pathogenic)
          • Incubation 1-7 days
          • Initial watery diarrhoea becomes frankly/uniformly blood-stained in 70%; often associated with severe and often constant abdominal pain
            • Whilst systemic features e.g. vomiting/fever, are mild/rare, the enterotoxin can affect other organs. In particular, the kidneys
              • Haemolytic uraemic syndrome occurs in 10-15% and occurs 5-7 days after symptom onset
              • Antibiotic treatment may precipitate this and so should be avoided.
        • Clostridium difficile
        • Yersinia enterocolitica
          • Usually found in undercooked pork products
          • Causes mild-moderate gastroenteritis and mesenteric adenitis (usually infection of children)
          • Incubation period 3-7 days
          • May take a while to resolve
        • Cholera
        • Shigella


  • Stool sample
    • Inspection for blood; microscopy for leucocytes, ova, cysts and parasites; culture for bacteria; and toxin test for C diff
  • FBC
  • U&Es- assess hydration, metabolic state and renal function


  • Hygiene and isolation (if possible; or minimal contact) are important to prevent spread
  • Consider admission in
    • Patients who are vomiting as well as diarrhoea (i.e. unable to retain water)
    • Patients with features of shock/severe dehydration
    • Possibly if a recent travel history of note, elderly patients, bloody diarrhoea, incontinence, co-existing medical conditions/drugs which may complicate or be complicated by the gastroenteritis e.g. poorly controlled BP, renal disease, diuretics etc
  • Fluid replacement
    • Fluid loss from infective diarrhoea is isotonic (i.e. both water and electrolytes are lost)
      • Replace both orally where possible with solutions like dioralyte.  If not possible, IV fluid/electrolyte replacement is required.
    • The volume of fluid replacement should be based on
      • Replacement of established deficit
        • 48 hours of moderate diarrhoea (6-10 stools/24 hours) => 2-4l (diarrhoea alone)
        • Rapid replacement of 1-1.5l (either oral or IV) within first few hours
          • If symptoms have been going on for longer or symptoms are severe, this can cause a metabolic acidosis and can be a medical emergency requiring fluid/electrolyte replacement
      • Replacement of ongoing losses
        • Average diarrhoeal stool ~200ml fluid
        • Fluid balance should be recorded appropriately
        • Sachets of dioralyte etc come in 200ml formulations (i.e. 1:1)
      • Replacement of normal daily requirement
        • i.e. 1-1.5l of fluid + 140mmol Na + 60mmol K
  • Antibiotics should ONLY be considered in patients with prolonged disease (with positive stool culture); confirmed Sh dysenteriae and in invasive salmonellosis (typhoid)
    • Antibiotics may be useful in epidemics but these are rare in the UK
  • Antidiarrhoeal agents, antimotility agents and antisecretory agents are not recommended (tend to prolong disease)

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