Key Facts

Gastroenteritis is one of the most common childhood illnesses worldwide. In the UK, it is usually self-limiting and caused by viral pathogens. The main risk is dehydration, particularly in young infants and those with high stool output. Management focuses on fluid replacement and nutritional maintenance.

Epidemiology

Gastroenteritis causes approximately 1.5 million GP consultations annually in UK children under 5. Before rotavirus vaccination (2013), rotavirus caused approximately 18,000 hospitalisations per year in England. Since vaccine introduction, rotavirus hospitalisations have fallen by approximately 80%. Norovirus is now the leading viral cause. Peak incidence is in winter months (norovirus, rotavirus) and summer (bacterial causes).

Aetiology

Viral (70-80%):

• Norovirus (most common post-rotavirus vaccination era)
• Rotavirus (declining with vaccination)
• Adenovirus (serotypes 40/41)
• Astrovirus, sapovirus

Bacterial (15-20%):

• Campylobacter (most common bacterial cause in UK)
• Salmonella
• Shigella
• E. coli (including STEC/O157 — associated with HUS)

Parasitic (rare in UK):

• Giardia lamblia, Cryptosporidium

Pathophysiology

Viral: Direct enterocyte invasion → villous blunting → reduced absorptive surface area → osmotic diarrhoea. Also disrupts brush border disaccharidases → temporary lactose intolerance.

Bacterial: Enterotoxin-mediated (watery diarrhoea — cholera, ETEC) or invasive (bloody diarrhoea — Shigella, Campylobacter, EIEC). Inflammation damages colonic mucosa.

STEC (E. coli O157): Produces Shiga toxin → endothelial damage → thrombotic microangiopathy → haemolytic uraemic syndrome (HUS) in ~5-10% of infected children.

Typical Presentation

• Acute onset diarrhoea (≥3 loose/watery stools per day)
• Vomiting (often precedes diarrhoea)
• Fever (low-grade, especially viral)
• Abdominal cramps
• Reduced oral intake

Dehydration Assessment (NICE CG84)

• No clinical dehydration: Alert, normal skin turgor, moist mucous membranes, normal CRT, normal urine output
• Clinical dehydration: Altered responsiveness, reduced skin turgor, dry mucous membranes, tachycardia, reduced urine output, sunken eyes
• Clinical shock: Decreased consciousness, pale/mottled, cold extremities, CRT >3 sec, tachycardia, hypotension, absent urine output

Red Flags

• Bloody diarrhoea — consider bacterial cause, especially STEC (E. coli O157); avoid antibiotics until STEC excluded
• Bilious (green) vomiting — surgical emergency until proven otherwise (malrotation/volvulus)
• Signs of shock — immediate IV fluid resuscitation
• Severe abdominal pain/distension — consider intussusception, surgical abdomen
• Fever >40°C, rigors, unwell child — consider sepsis, invasive bacterial infection
• Post-diarrhoeal pallor, petechiae, oliguria — haemolytic uraemic syndrome (HUS)

Bedside

• Clinical assessment of dehydration: Skin turgor, mucous membranes, CRT, HR, level of alertness
• Weight: Compare to recent known weight — % weight loss estimates dehydration severity (~5% = clinical dehydration, ≥10% = shock)
• Urine output monitoring: Wet nappies count, urine dipstick
• Capillary blood glucose: If drowsy or prolonged vomiting

Bloods

• Not routinely required for uncomplicated gastroenteritis (NICE CG84)
• If IV fluids required: U&Es, glucose, blood gas (assess electrolyte disturbance, acidosis)
• If bloody diarrhoea with anaemia/thrombocytopenia: FBC, blood film, U&Es, LDH, haptoglobin (HUS screen)

Imaging

• Not routinely indicated
• Abdominal USS: If intussusception suspected (target/doughnut sign)

Special Tests

• Stool MC&S: If bloody diarrhoea, immunocompromised, recent travel, symptoms >7 days, suspected STEC
• Stool virology: Rotavirus/norovirus/adenovirus rapid antigen testing
• E. coli O157/STEC screen: PCR or culture; do NOT give antibiotics until result available
• Stool ova and parasites: If travel to endemic areas or persistent diarrhoea

Non-pharmacological

• Oral rehydration: ORS (e.g., Dioralyte) 50ml/kg over 4 hours for clinical dehydration (NICE CG84); offer frequently in small volumes
• Continue breastfeeding: Do not stop breastfeeding during gastroenteritis
• Early refeeding: Resume normal diet as soon as rehydrated — do not withhold food
• Avoid fruit juice and carbonated drinks: High osmolality worsens diarrhoea
• Hand hygiene: Alcohol gel is NOT effective against norovirus — soap and water required
• Exclusion from school/nursery: 48 hours after last episode of vomiting/diarrhoea

Pharmacological

• IV fluids: 0.9% NaCl 20ml/kg bolus for shock; then replacement of deficit + maintenance over 24 hours
• Ondansetron: 0.15mg/kg (max 4mg) single oral/IV dose — consider if persistent vomiting prevents ORS (off-licence but widely used; NICE supports use)
• Antibiotics: NOT routine. Indicated for: confirmed Shigella (azithromycin 10mg/kg OD × 3 days), cholera, Giardia (metronidazole 7.5mg/kg TDS × 5-7 days), severe salmonella in immunocompromised
• Avoid: Loperamide (contraindicated in children), routine antibiotics, anti-emetics other than ondansetron

Surgical/Interventional

• Not applicable for gastroenteritis
• If HUS develops — supportive care, dialysis if needed

Referral Criteria

• Signs of shock — immediate hospital admission
• Unable to tolerate ORS, persistent vomiting — hospital for IV rehydration
• Bloody diarrhoea with systemic illness — hospital for STEC screen and HUS monitoring
• Age <3 months with temperature ≥38°C — hospital admission
• High-risk features: immunocompromised, comorbidities, malnourished

• Self-limiting in the vast majority: symptoms resolve within 5-7 days (viral) or 7-14 days (bacterial)
• Dehydration mortality: Very low in UK (<1 per million children per year) with appropriate management
• Post-infectious complications: Temporary lactose intolerance (2-6 weeks), post-infectious IBS
• HUS (E. coli O157): Develops in ~5-10% of STEC-infected children; mortality ~3-5%, ~25% have long-term renal sequelae
• Rotavirus vaccine has dramatically reduced severe disease — prevented an estimated 27,000 hospitalisations in the first 3 years post-introduction

NICE CG84 Dehydration Assessment

UK Rotavirus Vaccination Schedule