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While diarrhoea is commonly infectious, it can also be caused by malabsorption, drugs and other non-gastrointestinal pathologies. 


  • Causes of Diarrhoea

  • Inflammatory

  • Viral infection - rotavirus, norovirus, adenovirus
  • Bacterial infection - Campylobacter, Shigella, Salmonella, Escherichia coli, Clostridium difficile, Vibrio cholerae, Staph aureus
  • Parasitic infection - giardiasis
  • Inflammation - Crohn's disease, ulcerative colitis, diverticulitis, appendicitis, ischaemic colitis, radiation colitis, colorectal cancer
  • Fatty

  • Malabsorption - lactose / fructose intolerance, coeliac disease, mesenteric ischaemia, short bowel syndrome, amyloidosis, tropical sprue, Whipple disease
  • Exocrine deficiency - cholestasis, pancreatic exocrine insufficiency
  • Watery

  • Medications - laxatives, magnesium, antihypertensives, lipid-lowering meds, PPIs, NSAIDs, antibiotics, certain chemotherapy
  • Endocrine - hyperthyroidism, adrenocortical insufficiency
  • Neuroendocrine tumour - gastrinoma, VIPoma, carcinoid syndrome
  • GI neoplasia - colorectal cancer, lymphoma, villous adenoma
  • Alcohol abuse
  • Functional

  • Irritable bowel syndrome
Don't forget to check whether your patient is on laxatives, as this may be a simply treated cause for their diarrhoea.

History of Presenting Complaint

  • Stools

    The frequency, colour and consistency of the patient's stools.
  • Watery stoolsSuggestive of osmotic or secretory cause
  • Steatorrhoea: fatty stools that floatSuggestive of malabsorption or exocrine deficiency
  • Blood-stained stoolsSuggestive of inflammatory cause, e.g. infection, inflammation, ischaemia or tumour
  • High-volume diarrhoeaSuggestive of small bowel pathology
  • Increased frequency of small volume diarrhoeaSuggestive of large bowel pathology
  • Alternating diarrhoea and constipationSuggestive of irritable bowel syndrome (IBS)
  • Triggers

    Whether there was any inciting event prior to onset of the diarrhoea.
  • Post recent tavelSuggestive of infection, especially enterotoxic E coli
  • After eating seafoodSuggestive of Vibrio infection
  • During or after a course of antibioticsPotential Clostridium difficile infection
  • Associated Symptoms

    Whether the diarrhoea is associated with any other symptoms.
  • Nausea / vomitingSuggestive of inflammatory cause, particularly infection
  • Severe abdominal painSuggestive of inflammatory cause
  • FeversSuggestive of infectious cause
  • Weight lossSuggestive of malabsorption or cancer
  • Perianal discharge or fistulaSuggestive of inflammatory bowel disease
  • Severity

  • Whether the patient has been able to keep down any fluids, and how the diarrhoea is affecting their daily life.
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