Global Impact: Gastroenteritis is one of the leading causes of acute diarrhoea worldwide, particularly affecting 👶 young children, the elderly 👵, and immunocompromised patients.
Norovirus: 🦠 Responsible for >50% of outbreaks, especially in hospitals, care homes, cruise ships, and schools.
Rotavirus: 💉 Once the leading cause of severe diarrhoea in under-5s, now dramatically reduced in vaccinated populations.
Seasonality: Viral gastroenteritis peaks in ❄️ colder months in temperate climates; bacterial causes (e.g., food poisoning) occur year-round.
Transmission: Primarily fecal-oral ➡️ via contaminated food/water or person-to-person in crowded environments.

Viral Entry: Ingestion of contaminated food/water or contact with infected surfaces introduces pathogens (e.g., norovirus, rotavirus).
Enterocyte Damage: Viruses infect intestinal enterocytes → villous blunting → malabsorption of nutrients.
Electrolyte Loss: Disrupted absorption + increased secretion of water/electrolytes = watery diarrhoea 💧.
Vomiting: Triggered by norovirus via GI tract stimulation and activation of the vomiting centre 🤢.

Viral:
- Norovirus: Highly contagious, rapid spread in outbreaks.
- Rotavirus: Severe in children, prevented by vaccine.
- Adenovirus: Often in <2-year-olds, spread by close contact.
- Astrovirus: Elderly and children, via food/water.
- Enteric coronavirus: Mild, GI-focused illness.
Bacterial:
- Salmonella: Eggs, poultry, undercooked meat.
- E. coli (O157:H7): Severe diarrhoea, risk of HUS ⚠️.
- Campylobacter: Poultry, contaminated water.
- Shigella: Bloody diarrhoea, low-inoculum pathogen.
- C. difficile: Antibiotic-associated colitis, hospital-acquired 💊.
- Vibrio cholerae: Cholera, “rice-water stools” with rapid dehydration.
Parasitic:
- Giardia lamblia: Chronic watery diarrhoea from contaminated water (“beaver fever”).
- Entamoeba histolytica: Amoebic dysentery with risk of liver abscess 🩸.

Hydration: 🚰 ORS for mild/moderate dehydration; IV fluids if severe or vomiting prevents oral intake.
Antiemetics: Ondansetron for persistent vomiting (especially in children).
Antipyretics: Paracetamol/ibuprofen for fever and malaise.
Probiotics: Can shorten illness duration in children (modest benefit).
Antibiotics: ONLY if confirmed bacterial cause (e.g., Shigella, severe Campylobacter, C. difficile, cholera).
Dietary: Start light foods (bananas, rice, toast). Avoid dairy, caffeine, fatty foods until recovery.
Isolation: For norovirus (very contagious!) to prevent outbreaks.

Vaccination: Rotavirus vaccine part of child immunisation schedules worldwide 🌍.
Hand Hygiene: Soap + water 🧼 > alcohol gel for norovirus.
Safe Food Practices: Proper cooking, refrigeration, and avoidance of cross-contamination.
Disinfection: Chlorine-based cleaning in outbreak settings (schools, hospitals).
Isolation: Cohort patients with norovirus in hospitals and nursing homes.

💧 Most important treatment = rehydration (oral or IV).
🧪 Always consider C. difficile in hospitalised or post-antibiotic patients with diarrhoea.
👶 Vaccination against rotavirus prevents thousands of hospitalisations annually.
⚠️ Red flags: bloody diarrhoea, severe dehydration, altered mental status → urgent escalation.

Gastroenteritis in Adults