Inflammation of the stomach and intestinal epithelium ± submucosa.
Typically acute, infective, and appears soon after exposure to an agent.
Most cases are mild and never present to hospital.
Hospital admission/IV fluids may be needed in high-risk groups: diabetics, pregnant women, children, elderly, immunocompromised.

🦠 Causes

Viruses: Rotavirus, Adenovirus, Astrovirus, Norovirus.
Bacteria: Campylobacter, E. coli (O157), Salmonella, Shigella, Vibrio cholerae, Staph. aureus, Clostridium botulinum, Clostridium perfringens, Bacillus cereus, C. difficile.
Protozoa: Giardia lamblia, Entamoeba histolytica, Cryptosporidium parvum.
Toxins: Seafood, mushrooms, scombrotoxin, ciguatera poisoning.

⚙️ Mechanisms

Non-inflammatory diarrhoea: Vibrio cholerae, Enterotoxigenic E. coli → toxins stimulate fluid/electrolyte secretion.
Inflammatory diarrhoea: Shigella, Salmonella, Enteroinvasive E. coli → epithelial invasion, cytokine release, mucosal injury.

🧾 Notable Organisms & Presentations

🍗 Staph. aureus: Vomiting & cramps within 6h (meat/dairy). Rapid onset, toxin-mediated.
🍚 Bacillus cereus: “Fried rice syndrome.” Vomiting within 6h or diarrhoea later.
🐟 Scombrotoxin (scombroid fish): D+V, flushing, “burning mouth” within 1h. Histamine effect → treat with antihistamines, fluids.
🐠 Ciguatera fish poisoning: D+V, cramps, paraesthesia, reversal of hot/cold sensation. Symptoms may persist months.
🥚 Salmonella: D+V+fever within 12–48h (meat, eggs, chicken). May cause sepsis.
🤢 Norovirus: Explosive projectile vomiting ± diarrhoea. Incubation 12–48h. Highly contagious.
👶 Rotavirus: Common in children; watery D+V, fever, 1–7d incubation.
🥫 Clostridium botulinum: Vomiting, diplopia, paralysis → canned foods. Neurotoxin blocks acetylcholine release.
💊 C. difficile: Associated with antibiotics. Diarrhoea, pseudomembranous colitis, risk of toxic megacolon.
🥩 Clostridium perfringens: Diarrhoea/cramps after 8–24h (meat, stews).
🥛 Campylobacter: Bloody diarrhoea, fever, AP after 2–5d (poultry, milk). May trigger Guillain–Barré.
🌽 E. coli O157: Bloody diarrhoea, risk of haemolytic uraemic syndrome (HUS).
🥛 Yersinia enterocolitica: Diarrhoea, fever, AP (milk/pork). Can mimic appendicitis.
💧 Cryptosporidium: Watery diarrhoea (esp. HIV, immunosuppressed). From contaminated water.
🐕 Giardia lamblia: Chronic diarrhoea, malabsorption, bloating. Zoonotic (cats, dogs).
🌍 Entamoeba histolytica: Dysentery ± liver abscess. Endemic areas.
🥬 Shigella: Bloody diarrhoea, fever, AP within 2–3d (foodborne, faeco-oral).
🦪 Vibrio parahaemolyticus: D+V+AP from seafood, esp. shellfish.

🩺 Clinical Features

Acute nausea, vomiting, diarrhoea ± fever.
Colicky abdominal pain, ↑ bowel sounds.
Watery stools → may become bloody or mucoid.
Severe dehydration and hypotension in some cases.

🔬 Investigations

Most mild cases → no tests needed.
FBC/CRP: leukocytosis, inflammation.
U&E: check dehydration, renal function. Severe ↑ urea/creatinine → risk of AKI or HUS (E. coli O157).
Stool sample: microscopy, culture, toxin analysis.
Blood cultures: if pyrexial/septic.
AXR: may show dilated loops, no faeces (ileus).

🌍 Prevention When Abroad

Drink bottled/boiled water only.
Avoid ice cubes, raw salads; peel fruit yourself.
Eat freshly cooked hot food only.

💊 Management

Rehydration is key: ORS for mild cases, IV fluids for severe.
Symptomatic relief: loperamide/codeine (avoid if bloody diarrhoea or suspected E. coli O157).
Antibiotics (e.g. ciprofloxacin) only for severe/systemic cases (Salmonella, Shigella, Campylobacter in high-risk groups).
⚠️ Gastroenteritis is a notifiable disease in the UK.

⚠️ Important Complications

🧠 Guillain–Barré syndrome → Campylobacter.
🩸 Haemolytic uraemic syndrome (HUS) → E. coli O157.
💉 DKA precipitated in Type 1 DM (sick day rule failure).
🫀 Hypovolaemic shock.
💪 Botulinum toxin → neuromuscular weakness, paralysis.

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Viral Gastroenteritis and other causes

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