Enteric infection with viruses, bacteria or protozoa characterised by the sudden onset of diarrhoea, with or without vomiting.


  • About 20% of the population develop some form of gastroenteritis every year.  Only 1 in 6 will present to their GP and fewer will require investigation and active management.

Causes and features

  • Around 40% (the majority) of cases are caused by viruses
    • In adults, the most common cause is norovirus
      • Highly infectious and spread via faecal-oral route (personal contact, food, or surfaces- making hospital outbreaks a common problem).  Incubation period of 24-48 hours.  Symptoms usually last for 12-60 hours
        • Initial nausea; followed by watery diarrhoea +/- vomiting
          • Some people have fever, headache and myalgia.
        • Most cases are self-limiting and don’t require active treatment.  Some cases (particularly in the elderly) will require hospitalisation for hydration therapy.
    • In children, the most common cause is rotavirus (56% of childhood gastroenteritis; almost every child will have been infected by 5 years old)
      • Also highly infectious (but many individuals are immune following infection); spread by faecal-oral route; seasonal (Nov- April)
      • Symptoms- start with fever, vomiting is quite common, and followed by diarrhoea, which is usually watery.  Can last 3-9 days and can be mild-severe.
    • Adenovirus is the second most common cause in children, but are less common in adults.  Presentation is almost identical to that of other viral enteric infections.
  • Bacterial infection is usually more severe and may be notifiable.  Most cases are due to food poisoning
    • Campylobacter (gram negative proteobacteria) is the most common bacterial cause in the UK, particularly in children (compared to adults).  Spread either by person-person (faecal-oral route) or can be due to undercooked poultry, unpasteurised milk and transmission via pets with diarrhoea.  It is notifiable.
      • Incubation period of usually 2-5 days.  There can be prodromal illness of fever, headache, myalgia for 24 hours.
      • Diarrhoea is usually profuse (10/day)- often watery and can be bloody.  Can be accompanied by abdominal pain and tenderness (right iliac fossa > elsewhere).  Symptoms usually last a week.
    • Escherichia coli*** (gram negative rod) is common cause of diarrhoea.  E coli 0157:H7 is a particular strain that can cause a severe disease and haemolytic uraemic syndrome in 5-10% of people.   Spread by faecal oral route and caught from inadequately cooked infected beef products amongst other foods.  Also notifiable
      • Incubation period of around 3 days.
      • Acute bloody diarrhoea can develop over several days, usually accompanied by abdominal pain and fever.  Pallor, petechial rash and oliguria are signs of more severe disease.
        • NB if anaemia, thrombocytopenia and oliguria develop, these are the classic symptoms of HUS (require close management)
    • Salmonella (gram-negative rod) is becoming a less common cause of gastroenteritis.  Again spread by faecal-oral route and caught from contaminated animal products that has been inadequately cooked or has been unsuitably defrosted (classically buffet food)
      • Incubation period of 12-72 hours
      • Diarrhoea can be bloody starts with fever and abdominal cramps.  Illness tends to last 4-7 days.
    • Shigella (gram-negative rod) is a bacteria exclusively infecting humans, so is commonly caught/spread faecal-oral route from contaminated water (with human faeces).
      • Incubation is 12-48 hours
      • Diarrhoea is accompanied by mucus (dysentery), fever and abdominal cramps.  Illness tends to last 5-7 days.
      • Shigellosis is also another cause of HUS, and so patients (particularly young children and the elderly) should be monitored for this.
    • Other bacterial causes include toxin producing organisms e.g. Staph aureus, and Yersinia enterocolitica.
    • See also Clostridium difficile

***Note that there are two distinct types of E coli-

  1. enterotoxigenic- causes watery diarrhoea, mainly in young children or in developing countries (the infective dose is very high)
  2. enterohaemorrhagic- causes more severe bloody diarrhoea and is more seen in the UK (much higher infectivity)(see above)



  • Stool culture is the primary investigation, particularly if there is suspected bacterial infection (notifiable disease)
  • U&Es and FBC may want to be checked (but only if there is a risk of HUS/suspected HUS) to assess anaemia/renal function


  • Antibiotics are rarely required, nor are antidiarrhoeals.
  • It is important to assess hydration status and risk of HUS, as well as severity of disease, to determine whether to admit and address fluid balance.
    • In children, Oral Rehydration salts (ORS) are used, but in adults the evidence is lacking for their use.
  • Advise to avoid contact – off work/school for at least 48 hours

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