Key Facts

Gastroenteritis causes acute diarrhoea (≥3 loose stools/day) with or without vomiting. Most community-acquired cases are viral and self-limiting. Assessment of dehydration status and identification of patients requiring investigation or hospital admission are key primary care skills.

Epidemiology

• Estimated 17 million cases of infectious intestinal disease annually in England
• Norovirus: most common cause in adults, responsible for >3 million cases/year in UK
• Campylobacter: most common bacterial cause; incidence 100 per 100,000
• Salmonella: approximately 8,000 cases/year in UK
• Rotavirus cases in children reduced by >80% since vaccine introduction in 2013

Aetiology

• Viral: norovirus (most common in adults), rotavirus (children, now less common with vaccination), adenovirus, astrovirus
• Bacterial: Campylobacter jejuni (most common bacterial), Salmonella spp., Shigella, E. coli (STEC O157), Clostridium difficile, Staphylococcus aureus (toxin-mediated)
• Parasitic: Giardia lamblia, Cryptosporidium, Entamoeba histolytica (travel-related)
• Toxin-mediated: Bacillus cereus (reheated rice), Staphylococcus aureus (rapid onset <6 hours)

Pathophysiology

• Viral: invasion and destruction of enterocytes leading to villous blunting, reduced absorption, and secretory diarrhoea
• Bacterial: varies by organism — invasive (Campylobacter, Salmonella), toxin-mediated (S. aureus, B. cereus), cytotoxic (C. difficile, STEC)
• Toxin-mediated gastroenteritis typically has shorter incubation (<6 hours for preformed toxins)
• Dehydration results from fluid loss through diarrhoea and vomiting exceeding oral intake

Typical Viral Gastroenteritis

• Acute onset watery diarrhoea
• Nausea and vomiting (often prominent with norovirus)
• Abdominal cramps
• Low-grade fever
• Duration: 24-72 hours typically

Bacterial Gastroenteritis

• May present with bloody diarrhoea (Campylobacter, Shigella, STEC)
• Higher fever
• More severe abdominal pain
• Longer duration (5-7 days)
• Campylobacter: bloody diarrhoea with severe cramping, mimics appendicitis

Dehydration Assessment

• Mild: thirst, dry mucous membranes, reduced urine output
• Moderate: tachycardia, reduced skin turgor, sunken eyes
• Severe: hypotension, oliguria/anuria, altered consciousness

Red Flags

• Bloody diarrhoea — invasive bacterial infection, STEC (risk of HUS)
• Severe dehydration or inability to maintain oral intake
• Immunosuppressed patients — higher risk of complicated/prolonged illness
• Symptoms >7 days — consider non-infectious cause or parasitic infection
• Recent antibiotic use — C. difficile
• Recent travel — parasitic or tropical infections
• Outbreak setting — notification to public health required

Bedside

• Observations: HR, BP, temperature, capillary refill
• Assessment of hydration status
• Weight (especially in children)

Bloods

• Not routinely required for mild self-limiting gastroenteritis
• FBC, U&Es, CRP if systemically unwell or dehydrated
• Blood cultures if sepsis suspected

Microbiology

• Stool culture: recommended for bloody diarrhoea, immunocompromised, recent travel, >7 days duration, suspected outbreak, food handlers
• C. difficile toxin: if antibiotic-associated diarrhoea
• Stool ova, cysts, and parasites: if travel history or prolonged symptoms
• Norovirus PCR: in outbreak settings (care homes, hospitals)

Imaging

• Not routinely required
• Abdominal X-ray if concern about toxic megacolon or obstruction

Special Tests

• Faecal calprotectin: to differentiate IBD from functional bowel disease if chronic symptoms
• STEC testing: if bloody diarrhoea (request E. coli O157 culture + PCR for Shiga toxin)
• Giardia antigen test: if persistent diarrhoea with travel history or waterborne outbreak

Non-pharmacological

• Oral rehydration: first-line for all patients; oral rehydration salts (ORS) in moderate dehydration
• Maintain regular small sips of fluid
• Bland diet as tolerated; avoid dairy if significant vomiting
• Handwashing and infection control advice (48-hour rule after last episode for return to work/school)
• Advise food handlers to stay off work until 48 hours symptom-free

Pharmacological

• Loperamide: 4mg initially then 2mg after each loose stool (max 16mg/day) — for symptomatic relief in non-bloody, non-febrile gastroenteritis; avoid in bloody diarrhoea and suspected STEC
• Oral rehydration salts (Dioralyte): for moderate dehydration
• IV fluids (0.9% saline): if unable to maintain oral intake or severe dehydration

Antibiotics (only for specific indications):

• Campylobacter (if severe or immunocompromised): clarithromycin 250-500mg BD for 5 days or ciprofloxacin 500mg BD for 3 days
• Shigella (moderate-severe): ciprofloxacin 500mg BD for 3 days or azithromycin 500mg OD for 3 days
• Salmonella (only if invasive/bacteraemia or immunocompromised): ciprofloxacin 500mg BD for 5-7 days
• C. difficile: stop causative antibiotic; oral vancomycin 125mg QDS for 10 days (first-line per PHE guidance) or fidaxomicin 200mg BD for 10 days
• Giardia: metronidazole 400mg TDS for 5 days

Surgical

• Not applicable unless surgical complication (e.g. toxic megacolon, perforation)

Referral Criteria

• Severe dehydration or inability to maintain oral intake: hospital admission
• Suspected HUS (STEC, bloody diarrhoea, thrombocytopenia, renal failure): emergency referral
• Immunocompromised with severe infection: hospital admission
• Outbreak: notification to local Public Health team (notifiable disease)

• Viral gastroenteritis: self-limiting in >95% within 48-72 hours
• Campylobacter: resolution within 5-7 days in most; post-infectious IBS in 10-15%; Guillain-Barré syndrome risk 1 in 1,000
• Salmonella: carrier state in 1-5% after acute infection
• STEC O157: HUS develops in 5-15% of infected children; mortality of HUS 3-5%
• C. difficile: recurrence rate 20-30% after first episode; 40-60% after multiple recurrences
• Dehydration-related mortality: very low in UK with access to healthcare; higher risk in extremes of age

Common Causes by Incubation Period

When to Send Stool Samples