Brief Causes

Viral Gastroenteritis

  • Norovirus is the most common cause of viral infectious gastroenteritis in adults
  • Rotavirus is the most common cause of infantile gastroenteritis
  • Adenovirus commonly causes infections of the respiratory system but can also cause gastroenteritis, particularly in children.

Bacterial causes of infective diarrhoea:

  • Campylobacter
  • Escherichia coli
  • Salmonella (non-typhoidal)
  • Shigella

Parasitic causes of diarrhoea disease:

  • Cryptosporidium
  • Entamoeba histolytica
  • Giardia


Mild dehydration

  • Diarrhoea
  • Nausea.
  • Sudden onset of vomiting.
  • Blood or mucus in stool
  • Fever
  • Light headed
  • Postural hypotension

Moderate dehydration

  • Dizziness
  • Nausea
  • Headache
  • Muscle cramps
  • Dry tongue or sunken eyes
  • Reduced skin elasticity
  • Postural hypotension (Systolic blood pressure > 90 mmHg)
  • Tachycardia
  • Oliguria

Severe dehydration

  • Weakness
  • Confusion, leading to coma
  • Shock
  • Tachycardia
  • Marked peripheral vasoconstriction
  • Systolic blood pressure < 90 mmHg
  • Uraemia, oliguria, or anuria


Frequency of diarrhoea
Onset, quantity and duration of diarrhea
Course of symptoms – worsening or improving?
Precipitating factors for diarrhoea
Oral intake
Urine output
Weight loss
Mucus in stool (suggesting IBD)
Recent travel history
Recent suspect foods
Drug history explaining diarrhoea

  • Antibiotics (suggesting C.Difficile)
  • Anti-Malarials
  • Magnesium containing antacids

Vital signs / observations

Assess for dehydration and shock

  • Blood pressure
  • Temperature
  • Heart rate
  • Respiratory rate


  • Check for abdominal tenderness

Consider an alternative diagnosis if

  • Fever greater than 39 degrees:
  • Tachypnoea
  • Altered conscious state.
  • Neck stiffness
  • Non-blanching rash
  • Blood and/or mucus in stool
  • Bilious (green) vomit
  • Severe or localized abdominal pain or abdominal distension

Differential diagnoses

  • Food poisoning
  • C.Difficile infection
  • Non-gastrointestinal conditions e.g UTI, pneumonia
  • Gastrointestinal causes of chronic diarrhoea e.g IBS, IBD, coeliac disease
  • Drugs
  • Endocrinopathy
    • Diabetes
    • Hyperthyroidism

Laboratory investigations

The diagnosis of gastroenteritis is usually made on the basis of clinical symptoms and signs. Diagnostic investigations are rarely needed, but examination and culture of a stool sample may be necessary to determine the cause

Perform a stool sample analysis, if indicated, and consider the need for antibiotics if:

  • The patient is systemically unwell.
  • There is blood or pus in the stool.
  • The person is immunocompromised
  • There is a history of recent hospitalization and/or antibiotic treatment
  • Diarrhoea occurs after foreign travel
  • There is uncertainty about the diagnosis of gastroenteritis


The main goals of treatment of viral gastroenteritis are to prevent and treat volume depletion, maintain nutrition, and reduce spread to other people.


Give rehydration advice

  • In most otherwise healthy adults, encouraging fluid intake is sufficien
  • Consider supplementing fluid intake with oral rehydration salt solution in adults 60 years of age or older, frail, or with comorbidities where dehydration, hypovolaemia, or haemoconcentration would be a problem (for example cardiovascular disease or thrombotic tendencies).

Give hygiene advice to prevent spread of infection

  • Preventing the spread of infection
  • Advise the person that:
  • Wash hands thoroughly, especially before handling food
  • Do not share towels and clean handles and surfaces with detergent
  • They should not go to work or other institutional settings until at least 48 hours after diarrhoea and vomiting has stopped


Antidiarrhoeal (or anti motility), anti-emetic drugs and antibiotics are not usually necessary for the management of gastroenteritis. However, they may be useful for symptomatic control in adults

  • Loperamide is the antimotility drug of choice
  • Anti-emetics (e.g metoclopramide 10 mg IM) for severe vomiting
  • Antibiotics may be appropriate when gastroenteritis is due to a known microbiological cause (do not prescribe if the cause of diarrhoea is unknown)

Follow up

Notify Public Health if a notifiable disease (such as cholera) is diagnosed or suspected.
Advise the person to seek medical advice if:

  • Their condition does not improve within 48 hours.
  • Their symptoms worsen.
  • Warning signs or symptoms develop (e.g severe vomiting or dehydration, persistent fever, abdominal distension, blood in stools)


Typically a self-limiting condition lasting <14 days


  • Metabolic acidosis
  • Electrolyte imbalance due to volume depletion, loss of electrolytes, inadequate fluid and electrolyte resuscitation can cause serious electrolyte imbalances
    • Most commonly hypernatraemia, hyponatraemia, and hypokalaemia.
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