Infectious Diarrhoea (OSCE focused)

Candidate Instructions: You are a final-year medical student in a GP clinic. A 32-year-old patient presents with diarrhoea. 👉 Take a focused history, screen for red flags (dehydration, sepsis, dysentery, immunosuppression), suggest differentials, and outline initial investigations & management. ⏱️ You have 8 minutes. (No examination required.)

🔑 Key OSCE Learning Points

• Diarrhoea may be infective, inflammatory, malabsorptive, or functional – but infective causes are common 🦠.
• Always ask about exposures: food 🍗, water 💧, travel ✈️, contacts 👥, recent antibiotics 💊.
• ⚠️ Red flags: dehydration, bloody stool, sepsis features, pregnancy, extremes of age, immunocompromise.
• Infection control 🧼 is key → hand hygiene, stool precautions, isolation in hospital settings.

📝 History to Cover

• Onset & duration: hours–days (viral/bacterial) vs weeks (parasites/IBD).
• Stool character: watery 💦, bloody 🩸 (dysentery), mucoid, greasy/floating (Giardia/steatorrhoea).
• Associated symptoms: fever 🌡️, abdominal pain 🤢, vomiting 🤮, tenesmus, systemic upset.
• Exposure risks:
  • 💊 Recent antibiotics → C. difficile.
  • 🍗 Foodborne: undercooked chicken (Campylobacter, Salmonella).
  • 💧 Waterborne: Giardia, Cryptosporidium.
  • ✈️ Travel: traveller’s diarrhoea (ETEC, Shigella, amoebiasis).
  • 👥 Household/sexual contacts (Shigella, Hep A, proctitis).
• Risk groups: elderly, pregnant, immunosuppressed, chronic comorbidity.

👩‍⚕️ Examiner Prompts

• 💩 Watery diarrhoea for 2 weeks, occasional blood & mucus.
• 🌡️ Intermittent fevers.
• 📉 3 kg weight loss, tiredness.
• ✈️ Travel to India 1 month ago, ate street food.
• ❌ No recent antibiotics.

🔬 Investigations

• Bloods 🧪: FBC (anaemia, WCC), CRP/ESR, U&E (dehydration), LFTs.
• Stool tests 💩:
  • Stool microscopy/culture & sensitivity (Salmonella, Shigella, Campylobacter, E. coli O157).
  • Stool ova, cysts, parasites (Giardia, Entamoeba).
  • C. difficile toxin if recent antibiotics/hospital stay.
  • Faecal calprotectin (if IBD suspected).
• Other: HIV test if risk factors; colonoscopy if persistent or red flags.

🚑 Management

• General:
  • Hydration 💧 (oral/IV).
  • Diet: avoid dairy/fatty foods.
  • Infection control: handwashing 🧼, advise patient not to prepare food for others until 48h symptom-free.
• Specific causes:
  • 🦠 Viral gastroenteritis (norovirus, rotavirus): supportive only.
  • 🐔 Campylobacter/Salmonella: usually self-limiting; ciprofloxacin/azithromycin only if severe/systemic.
  • 💊 C. difficile: stop inciting antibiotic, start oral vancomycin/fidaxomicin, isolate patient.
  • 🧬 Giardia/amoebiasis: metronidazole or tinidazole.
  • ❌ Avoid antimotility drugs (loperamide) if bloody diarrhoea or systemic illness.
• Referral: hospital if severe dehydration, sepsis, immunocompromise, pregnancy, or red flags.

📋 Examiner’s Marking Guide

• Introduces self, explains task, gains consent 👍.
• History: duration, stool features, exposures, travel, antibiotics, red flags.
• Suggests correct investigations (stool culture, OCP, C. diff toxin).
• Mentions hydration, infection control, red flag referral 🚑.
• Identifies likely differential (infectious diarrhoea) and management plan.

⚖️ Common Infectious Differentials

• 🦠 Viral gastroenteritis (norovirus, rotavirus).
• 🐔 Bacterial food poisoning (Campylobacter, Salmonella, Shigella, E. coli O157).
• 💊 Antibiotic-associated diarrhoea (C. difficile).
• 🧬 Protozoa (Giardia, Entamoeba histolytica, Cryptosporidium).
• 🍃 Traveller’s diarrhoea (ETEC, Shigella, amoebiasis).

🧑‍⚕️ Case Examples - Infectious Diarrhoea

• Case 1 (Traveller’s diarrhoea - E. coli): 🌍 A 24-year-old backpacker returns from India with 3 days of watery diarrhoea and abdominal cramps. No blood, no fever. Stool cultures grow enterotoxigenic E. coli. Diagnosis: Traveller’s diarrhoea (ETEC). Teaching point: Most cases are self-limiting; managed with oral rehydration, antibiotics (azithromycin) only if severe or prolonged.
• Case 2 (Campylobacter enteritis): 🍗 A 35-year-old man develops fever, abdominal pain, and diarrhoea with blood streaks after eating undercooked chicken. Stool culture grows Campylobacter jejuni. Diagnosis: Bacterial gastroenteritis. Teaching point: Common cause of bloody diarrhoea in UK; usually supportive care, antibiotics (clarithromycin) if severe or immunocompromised.
• Case 3 (Clostridioides difficile infection): 💊 A 72-year-old woman, recently treated with co-amoxiclav for pneumonia, presents with profuse watery diarrhoea and abdominal tenderness. Stool test positive for C. difficile toxin. Diagnosis: C. difficile colitis. Teaching point: Antibiotic-associated diarrhoea; treat with oral vancomycin or fidaxomicin, and strict infection control.
• Case 4 (Norovirus gastroenteritis): 🚢 A 58-year-old cruise ship passenger develops sudden-onset vomiting and watery diarrhoea, with multiple other passengers affected. Diagnosis: Norovirus outbreak. Teaching point: Highly contagious viral cause of diarrhoea and vomiting; managed with fluids, isolation, and strict hand hygiene.
• Case 5 (Giardiasis): 💧 A 30-year-old hiker develops 2 weeks of foul-smelling, greasy diarrhoea, bloating, and weight loss after drinking untreated stream water. Stool antigen test positive for Giardia lamblia. Diagnosis: Giardiasis (protozoal diarrhoea). Teaching point: Causes chronic watery/malabsorptive diarrhoea; treat with metronidazole.