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Original Author(s): Dr Caroline Panto and Dr Hema Kannappa
Last updated: 29th December 2021
Revisions: 12

Original Author(s): Dr Caroline Panto and Dr Hema Kannappa
Last updated: 29th December 2021
Revisions: 12

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Infective gastroenteritis is very common, with many children having more than one episode per year (1). In a large number of cases it is a benign self-limiting illness. Despite this, many patients present to health care services and it can be a cause of significant morbidity and mortality.


Infective gastroenteritis is a temporary disorder due to an enteric infection. It is most commonly caused by viruses, but can also be due to bacterial or parasitic infection. It is typically characterised by sudden onset diarrhoea with or without vomiting.


Approximately 20% of the population will develop infectious gastroenteritis every year (1). The vast majority of patients do not have a stool sample sent. Public Health England reviewed laboratory reports over two weeks in 2014 and demonstrated that the most common isolates were Rotavirus and Campylobacter (3).  Adenovirus, which commonly results in respiratory infections, can also be a cause of gastroenteritis in children.

Viral causes of gastroenteritis


Most common cause of infantile gastroenteritis. The majority of children will have this infection before their 5th birthday (2). As immunity is long lasting, it is uncommon in adults. The rotavirus oral vaccine (Rotarix®) is part of the national vaccination programme in the UK. It is given at 8 and 12 weeks (4).  Rotavirus is spread by the faecal oral route or by environmental contamination, incidence peaks over the winter months.


Refers to a group of single stranded RNA viruses. They are the commonest cause of gastroenteritis in all age groups across England and Wales (2). Norovirus is spread by the faecal oral route or by environmental contamination.


It is more commonly known for causing infections of the respiratory system. However, they can also cause gastroenteritis, especially in those under 2 years of age.

Bacterial causes of gastroenteritis


This is the most commonly reported bacterial cause of gastroenteritis in the UK (2). It can cause bloody diarrhoea and is usually due to consumption of undercooked meat and unpasteurised milk.

Escherichia coli

Most strains of E-coli are harmless, however, some strains (verocytotoxin producing E-coli aka VETC) cause significant illness. A form of VTEC E.coli 0157:H7 can have the life threatening complications of haemorrhagic colitis and haemolytic uraemic syndrome (2). E.coli can be transmitted through contaminated food, person to person contact and contact with infected animals (for example at a petting farm!).

Clinical Features

Gastroenteritis is primarily a clinical diagnosis and therefore a careful history and examination should be performed. Clinical features suggestive of gastroenteritis include:

  • Sudden onset of loose/watery stool with or without vomiting
  • Abdominal pain/cramps
  • Mild fever
  • Recent contact with someone with diarrhoea or vomiting.

It is important to recognise those children who are at risk of dehydration. Those at greatest risk include (1):

  • Young children (especially under 6months).
  • Children who have passed >5 diarrhoeal stools in the last 24 hours.
  • Children who have vomited >2x in the last 24 hours.
  • Children who have stopped breast feeding during the illness.


NICE Guidance on assessing dehydration/shock (1)

                   Increasing severity of dehydration
No clinically detectable dehydration Clinical dehydration Clinical shock
Symptoms (remote and face-to-face assessments) Appears well Appears to be unwell or deteriorating
Alert and responsive  Altered responsiveness (for example, irritable, lethargic) Decreased level of consciousness
Normal urine output Decreased urine output
Skin colour unchanged Skin colour unchanged Pale or mottled skin
Warm extremities Warm extremities Cold extremities
Signs (face-to-face assessments) Alert and responsive  Altered responsiveness (for example, irritable, lethargic) Decreased level of consciousness
Skin colour unchanged Skin colour unchanged Pale or mottled skin
Warm extremities Warm extremities Cold extremities
Eyes not sunken  Sunken eyes
Moist mucous membranes (except after a drink) Dry mucous membranes (except for ‘mouth breather’)
Normal heart rate  Tachycardia Tachycardia
Normal breathing pattern  Tachypnoea Tachypnoea
Normal peripheral pulses Normal peripheral pulses Weak peripheral pulses
Normal capillary refill time Normal capillary refill time Prolonged capillary refill time
Normal skin turgor  Reduced skin turgor
Normal blood pressure Normal blood pressure Hypotension (decompensated shock)


Differential diagnosis

NICE state that a differential diagnosis should be considered if the child presents with:

  • Temperature higher than 38oC if < 3months or higher than 39oC if >3months.
  • Breathlessness or tachypnoea
  • Altered GCS
  • Meningism
  • Blood/mucous in stool
  • Bilious (green) vomit
  • Severe/localised abdominal pain.
  • Abdominal distension or guarding.


A stool sample should be sent for microbiological investigations if (1):

  • Septicaemia is suspected or
  • blood and/or mucus is present in the stool or
  • the child is immunocompromised

Do not routinely perform blood tests however measure Na+, K+, Cr, Ur and glucose if (1):

  • IV fluids are going to be used.
  • There are symptoms/signs of hypernatraemia (jittery, increased muscle tone, hyperreflexia, convulsions, drowsiness or coma).

Measure acid-base status and chloride concentration if shock is suspected.


From NICE guidelines (1)


If not clinically dehydrated:

  • Continue breast feeding/other milk feeds
  • Encourage fluid intake
  • Discourage fruit juices and carbonated drinks especially if the child is at risk of dehydration.
  • Offer oral rehydration salt solution (ORS) as supplemental fluid to those at risk of dehydration.


If dehydrated:

  • Only use IV therapy if:
    • Shock is suspected
    • In a child with any red flag symptoms
    • If there is evidence of dehydration despite use of oral rehydration therapy
    • If the child persistently vomits when ORS solution is given either orally or via NG tube.
  • Oral therapy: (all children unless they have the above indications for IV therapy)
    • Give ORS solution: 50 ml/kg over 4 hours to replace the defecit plus maintenance fluid*
    • Give the ORS solution frequently in small amounts e.g. 5ml every 5 minutes and consider supplementation with their usual fluids (including milk feeds or water, but not fruit juices or carbonated drinks)
    • If the child is refusing the oral fluid then consider a NG tube.


*Maintenance fluid calculation:

Child’s Weight (kg)  Fluid requirement for 24 hours
0-10kg 100ml/kg/day
10-20kg  Requirement for the 1st 10kg (i.e. 1000ml)+ 50ml/kg/day
>20kg Requirement for the 1st 20kg (i.e.1500ml) + 20ml/kg/day


Following rehydration:

Advise parents to give full strength milk straight away, and slowly re-introduce the child’s solid food. Suggest that fruit juices and carbonated drinks are avoided until the diarrhoea has resolved.

To avoid spread families should receive advice on hand washing and avoiding sharing of towels. The child should not return to their school/nursery until at least 48 hours have passed since the last episode of diarrhoea or vomiting, and the child should not swim for 2 weeks after the last episode (1).


Diarrhoea symptoms tend to last 5-7 days with the majority stopping within 2 weeks. Vomiting tends to last 1-2 days with the majority stopping within 3 days (1).

Haemolytic uraemic syndrome (HUS)

  • Rare but serious complication of acute infectious gastroenteritis that occurs mostly in young children and the elderly.
  • This can be a life-threatening complication causing:
    • acute renal failure,
    • haemolytic anaemia


Reactive complications associated with bacterial gastroenteritis

  • Including arthritis, carditis, urticaria, erythema nodosum and conjunctivitis.
  • REMEMBER: Reiter’s syndrome (the combination of urethritis, arthritis, and uveitis).


Toxic megacolon

  • This is a rare but significant complication of rotavirus gastroenteritis.


Acquired /secondary lactose intolerance

  • Occurs due to the lining of the intestine being damaged.
  • Leads to symptoms of bloating, abdominal pain, wind and watery stools after drinking milk.
  • Improves when infection resolves and gut lining heals (5).


(1) NICE (2009), Diarrhoea and vomiting caused by gastroenteritis in under 5s: diagnosis and management. Available at: Accessed 24/11/2016
(2) NICE (2015) Clinical Knowledge Summary. Gastroenteritis, Available at: Accessed 24/11/16
(3) Public Health England: Common gastrointestinal infections, England and Wales: Laboratory reports weeks 49 to 52, 2014. Available at: 24/11/2016
(4) Public Health England: The complete immunisation schedule from summer 2016. Available at: Accessed 28/11/2016
(5) Knott. L (2014) Gastroenteritis in Children. Patient. Avaliable at: Accessed on 28/11/20016



1st Author: Dr Caroline Panto

Senior reviewer: Dr Hema Kannappa, Paediatric ST8