Global Impact: Acute gastroenteritis is a common cause of diarrhoea and vomiting worldwide. It particularly affects 👶 young children, older adults 👵, and immunocompromised patients.
Most cases in the UK are viral and self-limiting.

🌍 Epidemiology

Norovirus: 🦠 The most common cause of outbreaks in the UK, especially in hospitals, care homes, schools, and cruise ships.
Rotavirus: Previously the leading cause of severe diarrhoea in young children; incidence has fallen significantly since introduction of routine vaccination.
Seasonality: Viral gastroenteritis often peaks in winter months in temperate climates.
Transmission: Faecal–oral spread via contaminated food, water, surfaces, or person-to-person contact.

⚙️ Pathophysiology

Viral infection: Pathogens infect intestinal epithelial cells (enterocytes).
Villous damage: Disruption of absorption causes malabsorption of electrolytes and water.
Secretory diarrhoea: Increased fluid secretion leads to watery diarrhoea 💧.
Vomiting: Stimulation of the enteric nervous system and vomiting centre causes nausea and vomiting 🤢.

📊 Causes of Gastroenteritis – Key Differences

Organism	Typical Clinical Features	Key Clues / Complications
Norovirus	Sudden vomiting, watery diarrhoea, abdominal cramps	Explosive outbreaks in hospitals, schools, cruise ships
Rotavirus	Vomiting followed by watery diarrhoea and fever	Common in infants; risk of dehydration
Adenovirus (enteric)	Watery diarrhoea lasting several days	Often affects young children
Campylobacter	Fever, abdominal pain, diarrhoea (often bloody)	Associated with undercooked poultry; may trigger Guillain–Barré syndrome
Salmonella	Diarrhoea, fever, abdominal cramps	Eggs, poultry, reptiles; bacteraemia in vulnerable patients
Shigella	Severe abdominal pain and bloody diarrhoea	Very low infectious dose; causes dysentery
E. coli O157	Severe abdominal pain with bloody diarrhoea	Risk of haemolytic uraemic syndrome (HUS)
Clostridioides difficile	Watery diarrhoea, abdominal pain, fever	Occurs after antibiotics or hospitalisation
Giardia lamblia	Chronic diarrhoea, bloating, flatulence	Malabsorption after contaminated water exposure
Entamoeba histolytica	Bloody diarrhoea and abdominal pain	May cause liver abscess

🔬 Investigations

Usually not required in mild, self-limiting gastroenteritis.
Stool culture/PCR may be indicated if:

Severe illness or dehydration
Bloody diarrhoea
Immunocompromised patient
Recent foreign travel
Suspected outbreak
Recent antibiotic use (test for C. difficile)

Blood tests (U&E): If dehydration or severe illness suspected.

💊 Management

Rehydration (most important treatment):

🚰 Oral rehydration solution (ORS) for mild–moderate dehydration.
💧 IV fluids if severe dehydration or unable to tolerate oral fluids.

Diet:

Continue normal diet if tolerated.
Avoid dehydration by encouraging frequent small drinks.

Antiemetics:

May be considered in severe vomiting in hospital settings.

Antibiotics:

Not routinely required.
Consider only in specific confirmed infections or severe bacterial disease.

Avoid anti-diarrhoeal medicines in young children or if invasive bacterial infection suspected.

🛡️ Infection Control

Strict hand hygiene with soap and water 🧼 (alcohol gel less effective against norovirus).
Exclude symptomatic individuals from work/school until 48 hours after symptoms stop.
Environmental cleaning with chlorine-based disinfectants during outbreaks.
Isolation or cohort nursing in healthcare settings if norovirus suspected.

⚠️ Red Flags

Signs of severe dehydration (confusion, hypotension, oliguria).
Persistent vomiting preventing oral intake.
Bloody diarrhoea.
High fever or systemic illness.
Symptoms lasting >7 days.
Very young infants, frail elderly, or immunocompromised patients.

📌 Key Clinical Pearls

💧 Rehydration is the cornerstone of treatment.
🦠 Most cases are viral and resolve within a few days.
⚠️ Always consider C. difficile in patients with recent antibiotic exposure.
🧼 Good hand hygiene is essential to prevent outbreaks.

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Gastroenteritis in Adults ✅

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