Acute and Chronic Diarrhoea ✅

💧 Diarrhoea is increased stool frequency, looseness or volume. The key first step is to assess hydration, sepsis risk, blood in stool, abdominal signs and red flags. Most acute cases are infective and self-limiting, but chronic or bloody diarrhoea needs careful assessment for IBD, colorectal cancer, malabsorption, endocrine disease and drug causes.

📌 Definition

• Diarrhoea: increased stool water content, frequency or volume.
• Objective definition: stool weight >200 g/day, though this is rarely measured clinically.
• Acute diarrhoea: <14 days.
• Persistent diarrhoea: 14 days to 4 weeks.
• Chronic diarrhoea: >4 weeks.
• Steatorrhoea: bulky, pale, oily, floating, offensive stools due to fat malabsorption.

🧠 Mechanism-Based Types of Diarrhoea

• 💦 Osmotic diarrhoea:
  • Occurs when poorly absorbed substances retain water in the bowel lumen.
  • Usually improves or stops with fasting.
  • Examples: lactose intolerance, sorbitol, magnesium-containing antacids, laxatives, coeliac disease.
  • Clues: bloating, flatulence, symptoms after specific foods, acidic stool in carbohydrate malabsorption.
• 🚰 Secretory diarrhoea:
  • Active secretion of water and electrolytes into the gut.
  • Typically persists despite fasting and may occur overnight.
  • Examples: enterotoxigenic infection, bile acid diarrhoea, microscopic colitis, endocrine tumours, laxative abuse.
  • Clues: large-volume watery diarrhoea, dehydration, nocturnal symptoms.
• 🔥 Inflammatory / exudative diarrhoea:
  • Mucosal inflammation causes leakage of blood, mucus, protein and inflammatory cells.
  • Examples: ulcerative colitis, Crohn’s disease, infective colitis, ischaemic colitis, colorectal cancer.
  • Clues: blood, mucus, fever, abdominal pain, raised CRP, raised faecal calprotectin, systemic symptoms.
• 🧈 Fatty / malabsorptive diarrhoea:
  • Failure to absorb fat, carbohydrate, bile salts or nutrients.
  • Examples: coeliac disease, pancreatic exocrine insufficiency, chronic pancreatitis, small bowel bacterial overgrowth, ileal disease or resection.
  • Clues: bulky pale offensive floating stools, weight loss, anaemia, vitamin deficiency, low albumin.
• ⚡ Functional diarrhoea / IBS-D:
  • Altered gut–brain interaction and visceral hypersensitivity without structural disease.
  • Examples: irritable bowel syndrome with diarrhoea predominance.
  • Clues: recurrent abdominal pain related to defecation, bloating, variable stool form, no red flags.
• 🪨 Overflow diarrhoea:
  • Loose stool leaks around faecal impaction.
  • More common in older adults, immobility, neurological disease and opioid use.
  • Clues: constipation history, faecal loading, rectal mass of stool, alternating constipation and diarrhoea.

🚩 Red Flags

• 🩸 Blood in stool or persistent rectal bleeding.
• ⚖️ Unintentional weight loss.
• 🌙 Nocturnal diarrhoea.
• 🔥 Fever, sepsis or systemic toxicity.
• 💧 Severe dehydration, hypotension, confusion or reduced urine output.
• 🤢 Persistent vomiting preventing oral hydration.
• 🧓 Older age with new change in bowel habit.
• 👨‍👩‍👧 Family history of colorectal cancer or inflammatory bowel disease.
• 🧱 Abdominal mass or rectal mass.
• 💊 Recent antibiotics, hospital admission or suspected Clostridioides difficile.
• ✈️ Recent travel, outbreak exposure, contaminated food or immunosuppression.

🦠 Acute Diarrhoea - Common Causes

• Viral gastroenteritis: norovirus, rotavirus; watery diarrhoea, vomiting, outbreaks.
• Bacterial gastroenteritis: Campylobacter, Salmonella, Shigella, STEC/E. coli; fever, abdominal pain, sometimes blood.
• Food toxin illness: rapid vomiting/diarrhoea after food exposure, e.g. Staphylococcus aureus, Bacillus cereus.
• Parasitic infection: Giardia, Cryptosporidium, Entamoeba; persistent diarrhoea, bloating, travel or water exposure.
• C. difficile infection: watery diarrhoea after antibiotics, healthcare exposure or frailty.
• Drug-related: antibiotics, metformin, PPIs, NSAIDs, chemotherapy, colchicine, laxatives, magnesium preparations.
• Acute IBD flare: bloody diarrhoea, urgency, abdominal pain, raised inflammatory markers.
• Ischaemic colitis: sudden abdominal pain and bloody diarrhoea, often in older patients or vascular disease.

⏳ Chronic Diarrhoea - Important Causes

• Inflammatory bowel disease: Crohn’s disease or ulcerative colitis.
• Coeliac disease: diarrhoea, bloating, anaemia, weight loss or fatigue.
• Bile acid diarrhoea: watery urgency, often post-cholecystectomy or ileal disease.
• Microscopic colitis: chronic watery diarrhoea, often older adults; associated with NSAIDs, PPIs and SSRIs.
• IBS-D: abdominal pain, bloating and altered stool without red flags.
• Colorectal cancer: change in bowel habit, bleeding, iron deficiency anaemia, weight loss.
• Pancreatic exocrine insufficiency: steatorrhoea, weight loss, diabetes, chronic pancreatitis history.
• Endocrine causes: thyrotoxicosis, diabetes-related autonomic neuropathy, adrenal insufficiency.
• Medication-related: metformin, laxatives, antibiotics, PPIs, NSAIDs, SSRIs, orlistat, colchicine.
• Overflow diarrhoea: faecal impaction with leakage of loose stool.

🩺 Clinical Assessment

• 📅 Duration: acute, persistent or chronic.
• 💩 Stool pattern: watery, bloody, mucus, fatty, nocturnal, high-volume or urgency.
• 💧 Assess hydration: thirst, postural dizziness, tachycardia, dry mucosa, capillary refill, urine output.
• 🌡 Check for fever, sepsis, abdominal tenderness, guarding or distension.
• 🍽 Ask about food exposures, sick contacts, outbreaks, care home, nursery or healthcare work.
• ✈️ Ask about travel, camping, untreated water and swimming exposure.
• 💊 Review drugs carefully, including antibiotics, laxatives, metformin, PPIs and NSAIDs.
• 🩸 Ask about rectal bleeding, weight loss, nocturnal symptoms and family history.
• 👆 Perform abdominal examination and consider digital rectal examination if constipation, overflow, bleeding or mass is possible.

🔍 Investigations - Acute Diarrhoea

• Most mild acute cases: no investigations needed if self-limiting and patient is well.
• Bloods if unwell or dehydrated: FBC, U&E, creatinine, LFTs, CRP, glucose.
• Stool culture/PCR if indicated: blood or mucus, severe symptoms, fever, sepsis, immunocompromise, recent travel, outbreak risk, food handler, healthcare worker, or persistent symptoms.
• C. difficile testing: if recent antibiotics, healthcare exposure, frailty, care home exposure or unexplained acute diarrhoea with risk factors.
• Ova, cysts and parasites: persistent diarrhoea, travel, camping, untreated water exposure or immunocompromise.
• Blood cultures: if septic, febrile and systemically unwell.
• Abdominal imaging: if severe pain, distension, suspected obstruction, toxic megacolon, perforation or ischaemic colitis.

🔍 Investigations - Chronic Diarrhoea

• FBC, U&E, LFTs, CRP or ESR.
• Ferritin, B12, folate, calcium, albumin if malabsorption suspected.
• Coeliac screen: tissue transglutaminase IgA plus total IgA.
• Thyroid function tests.
• Faecal calprotectin if IBD is possible and cancer is not suspected.
• Stool cultures and parasites if infection risk or persistent symptoms after travel.
• FIT testing or urgent colorectal referral if cancer features are present, according to local pathway.
• Colonoscopy if red flags, raised calprotectin, persistent unexplained diarrhoea, suspected microscopic colitis or suspected colorectal cancer.
• Consider bile acid diarrhoea testing or empirical pathway depending on local service.

💊 Management - General Principles

• 💧 Rehydration is the cornerstone: encourage fluids and oral rehydration solution if at risk of dehydration.
• 🏥 Admit or urgently assess: shock, severe dehydration, sepsis, severe abdominal pain, peritonism, toxic megacolon, frailty with inability to maintain fluids, or significant comorbidity.
• 🍽 Diet: continue light food as tolerated; avoid alcohol and very fatty foods during recovery.
• 🧼 Infection control: handwashing, avoid food preparation for others, and stay off work/school until 48 hours after last diarrhoeal episode if infectious gastroenteritis suspected.
• 🚫 Avoid antimotility drugs: if bloody diarrhoea, fever, suspected invasive infection, suspected C. difficile, severe colitis or toxic megacolon risk.
• 💊 Antibiotics: not routinely needed for most acute diarrhoea; use only when clinically indicated and guided by local microbiology advice.
• 🔁 Review: safety-net if worsening, persistent symptoms, dehydration, blood, fever or new red flags.

🧫 Specific Patterns & Management

• 🦠 Viral gastroenteritis:
  • Watery diarrhoea, vomiting, short duration, outbreak pattern.
  • Treat with fluids, oral rehydration solution if needed, antiemetic only if appropriate.
• 🧫 Bacterial gastroenteritis:
  • May cause fever, abdominal pain and blood or mucus.
  • Send stool sample if severe, bloody, persistent, travel-related or public health risk.
  • Antibiotics are not routine; discuss severe, high-risk or suspected specific infections with microbiology.
• 💊 C. difficile infection:
  • Suspect after antibiotics, hospital admission, care home exposure or frailty.
  • Stop unnecessary antibiotics and gastric acid suppression where safe.
  • Treat according to local antimicrobial guidance, commonly oral vancomycin or fidaxomicin depending on severity and recurrence risk.
  • Avoid loperamide unless specialist advised.
• 🔥 Inflammatory bowel disease flare:
  • Bloody diarrhoea, urgency, abdominal pain, raised CRP or faecal calprotectin.
  • Exclude infection, especially C. difficile, in known IBD flares.
  • Assess severity and involve gastroenterology if moderate/severe, systemic features or acute severe colitis.
• 🧈 Coeliac disease:
  • Chronic diarrhoea, bloating, anaemia, fatigue, weight loss or mouth ulcers.
  • Check coeliac serology while still eating gluten.
  • Confirm diagnosis before starting a gluten-free diet unless specialist advice says otherwise.
• 🥛 Lactose intolerance:
  • Osmotic diarrhoea, bloating and flatulence after dairy.
  • Improves with lactose reduction or lactase replacement.
• 💧 Bile acid diarrhoea:
  • Watery urgency, often post-cholecystectomy, ileal Crohn’s or ileal resection.
  • Consider gastroenterology assessment and bile acid sequestrant treatment if confirmed or strongly suspected.
• 🧬 Microscopic colitis:
  • Chronic watery, often nocturnal diarrhoea with usually normal-looking colonoscopy.
  • Diagnosis requires colonic biopsies.
  • Review triggers such as NSAIDs, PPIs and SSRIs; specialist treatment may include budesonide.
• 🪨 Overflow diarrhoea:
  • Suspect in older adults, immobility, opioids, dementia or constipation history.
  • Perform rectal examination where appropriate.
  • Treat faecal impaction and address constipation prevention.

⚠️ Known IBD - Exclude Coexisting Infection

🧫 In a patient with known IBD and worsening diarrhoea, do not assume every flare is inflammatory. Send stool testing for infection, especially C. difficile, if clinically indicated. Acute severe colitis is a medical emergency and needs urgent gastroenterology input.

🟢 Mild Colitis

• Typically fewer stools, minimal systemic upset and no significant fever, tachycardia or anaemia.
• Check stool cultures and C. difficile if infection is possible.
• Manage according to known diagnosis and local IBD plan.
• Consider topical therapy for distal ulcerative colitis where appropriate.
• Safety-net: worsening bleeding, fever, tachycardia, dehydration or increasing stool frequency needs urgent review.

🔴 Acute Severe Colitis

• Suspect if frequent bloody stools with systemic toxicity, fever, tachycardia, anaemia, raised inflammatory markers or abdominal distension.
• Admit urgently and involve gastroenterology.
• Investigations: FBC, U&E, LFTs, CRP, albumin, stool culture, C. difficile testing, abdominal X-ray if severe/distended, and limited flexible sigmoidoscopy if appropriate.
• Treatment usually includes IV fluids, VTE prophylaxis unless contraindicated, and IV corticosteroids such as hydrocortisone or methylprednisolone under specialist guidance.
• Avoid loperamide and opioids because of toxic megacolon risk.
• Monitor closely for toxic megacolon, perforation and need for rescue therapy or surgery.

🚑 When to Refer or Admit

• Severe dehydration, shock, sepsis or inability to maintain oral fluids.
• Bloody diarrhoea with systemic features.
• Suspected acute severe colitis.
• Severe abdominal pain, guarding, distension or suspected surgical abdomen.
• Immunocompromised patient with significant diarrhoea.
• Persistent diarrhoea with weight loss, anaemia, nocturnal symptoms or raised inflammatory markers.
• Suspected colorectal cancer or abdominal/rectal mass.
• Suspected malabsorption with weight loss or nutritional deficiency.

📝 Exam Pearls

• 💧 First question in acute diarrhoea: “Are they dehydrated, septic or bleeding?”
• 💦 Osmotic diarrhoea improves with fasting; secretory diarrhoea often continues overnight and during fasting.
• 🔥 Blood and mucus suggest inflammatory diarrhoea until proven otherwise.
• 🧈 Floating, oily, offensive stools suggest fat malabsorption.
• 🪨 In older adults, “diarrhoea” may actually be overflow from faecal impaction.
• 🧫 In known IBD, always consider infection, especially C. difficile.
• 🚫 Avoid loperamide in bloody diarrhoea, suspected C. difficile or severe colitis.
• 🧪 Faecal calprotectin helps distinguish inflammatory bowel disease from functional bowel disease, but it is not a cancer test.

🧠 Teaching Note

🧠 A useful way to understand diarrhoea is to ask: is water being pulled in, pushed out, leaked out, or not absorbed? Osmotic diarrhoea pulls water into the bowel, secretory diarrhoea actively pushes fluid into the lumen, inflammatory diarrhoea leaks blood and mucus through damaged mucosa, and malabsorptive diarrhoea reflects failure to absorb nutrients or fat. This mechanism-based approach helps link symptoms to causes: lactose intolerance causes bloating and osmotic diarrhoea, cholera-like toxins cause large-volume secretory diarrhoea, IBD causes inflammatory diarrhoea, and pancreatic insufficiency causes steatorrhoea.

📚 References & UK Resources

• NICE CKS – Diarrhoea: adult assessment
• NICE CKS – Gastroenteritis
• NICE CKS – Ulcerative colitis
• British Society of Gastroenterology – Chronic diarrhoea investigation