Diarrhoea

Introduction

Diarrhoea is defined as the passage of three or more loose or watery stools per day, or an increase in stool frequency beyond the patient’s normal pattern. It may be acute (<14 days), persistent (14–30 days), or chronic (>30 days). Causes range from infectious to inflammatory, functional, and malabsorptive disorders.

Peak Incidence

• Children aged 2–10 years – typically due to viral or bacterial gastroenteritis.
• Older adults (≥60 years) – commonly due to medication, chronic disease, or infections like Clostridioides difficile.

Pathophysiology

Diarrhoea can arise through several mechanisms:

• Osmotic: non-absorbed solutes draw water into the bowel (e.g. lactose intolerance).
• Secretory: excess fluid secretion into the intestine (e.g. enterotoxins from Vibrio cholerae).
• Inflammatory: mucosal damage leads to exudation (e.g. IBD, infections).
• Motility-related: reduced transit time (e.g. IBS, hyperthyroidism).

Symptoms

• Loose or watery stools (≥3 per day)
  • May be bloody or contain mucus in inflammatory/infectious causes
• Abdominal pain or cramping
• Nausea and vomiting
• Signs of dehydration: dry mouth, dizziness, low urine output

Signs

• Fever (in infectious or inflammatory causes)
• Tachycardia and hypotension (especially in dehydration)
• Abdominal tenderness
• Dehydration indicators:
  • Sunken eyes
  • Dry mucous membranes
  • Poor skin turgor
  • Capillary refill delay

Diagnosis

Clinical Assessment

• Duration, frequency, stool consistency, travel history, recent antibiotic use, immunocompromised status
• Red flag symptoms (e.g. blood in stool, weight loss, nocturnal symptoms)

Stool Analysis

• Stool culture and microscopy
  • Indicated if symptoms last >3 days, or in high-risk groups (elderly, immunocompromised, recent travel, or hospitalisation)
• Toxin assays (e.g. C. difficile)
• Faecal calprotectin (to assess for IBD if chronic or inflammatory symptoms present)

Blood Tests

• FBC – check for leukocytosis or anaemia
• U&Es – raised urea:creatinine ratio suggests dehydration; assess electrolytes (e.g. hypokalaemia)
• VBG/ABG – metabolic acidosis in severe dehydration
• CRP – inflammatory marker if IBD suspected

Imaging

• Abdominal X-ray – to assess for obstruction or megacolon
• CT abdomen/pelvis – if severe pain or suspected complications (e.g. abscess, perforation)

Endoscopy (if chronic or diagnostic uncertainty)

• Colonoscopy – to assess for IBD, malignancy, microscopic colitis, or ischaemia

Complications

• Dehydration and electrolyte imbalance (e.g. hypokalaemia)
• Sepsis – especially in elderly or immunocompromised patients
• Haemolytic uraemic syndrome (HUS) – associated with E. coli O157:H7
• Reactive arthritis – following Shigella, Salmonella, Yersinia infections
• Guillain–Barré syndrome – post-Campylobacter jejuni infection
• Malabsorption and weight loss – in chronic causes (e.g. coeliac disease, Crohn’s)

Management

Supportive Care (First-Line)

• Oral rehydration therapy (ORT) – cornerstone of treatment in mild to moderate cases
• Intravenous fluids – for moderate/severe dehydration or if unable to tolerate ORT
• Antidiarrhoeal agents:
  • Loperamide can be used in non-infectious, non-bloody diarrhoea (avoid in suspected infective or toxin-producing cases)
• Probiotics:
  • May be helpful in shortening the duration of infectious diarrhoea (evidence modest)

Antibiotic Therapy (Only if Indicated)

• Bacterial gastroenteritis:
  • Usually self-limiting; antibiotics considered only in severe disease or high-risk groups
  • Campylobacter, Salmonella, Shigella: consider macrolide or fluoroquinolone in high-risk cases
• C. difficile infection:
  • First-line: Oral vancomycin
  • Alternative: Fidaxomicin (if available)
  • Avoid loperamide in suspected or confirmed cases

Treat Underlying Cause

• Dietary modification

  • E.g. gluten-free diet in coeliac disease, lactose restriction in lactase deficiency

• Chronic conditions

  • Tailored treatment for IBD, IBS, or pancreatic insufficiency