Gastroenteritis — UKMLA Guide 2026

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This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.

Key points

Viral: norovirus (most common cause in adults — "winter vomiting bug"), rotavirus (most common in children pre-vaccine; now vaccinated in UK). Self-limiting 1-3 days
Bacterial: Campylobacter (most common bacterial cause in UK — from undercooked poultry), Salmonella, Shigella, E. coli O157 (bloody diarrhoea + HUS risk). Stool culture if bloody/severe/prolonged/traveller
Management: oral rehydration is the cornerstone. Antibiotics NOT routinely indicated (most are self-limiting). Avoid anti-motility agents (loperamide) in bloody diarrhoea or suspected E. coli O157
Send stool MC&S: if bloody diarrhoea, severe/prolonged (>7 days), immunocompromised, recent travel, recent antibiotics (C. diff), suspected outbreak
Notifiable organisms: Campylobacter, Salmonella, Shigella, E. coli O157 — notify local HPT. Food handlers must be excluded from work until 48 hours symptom-free

Overview

Gastroenteritis is inflammation of the stomach and intestines caused by infectious agents — viral, bacterial, or parasitic. The vast majority of cases are viral and self-limiting. Bacterial gastroenteritis is important to recognise because certain organisms (E. coli O157, Shigella) can cause serious complications and require public health notification. The key clinical distinction is between watery diarrhoea (typically viral or toxin-mediated) and bloody/dysenteric diarrhoea (typically invasive bacterial — Campylobacter, Shigella, E. coli O157, Salmonella). Food poisoning organisms cause disease either by preformed toxin (rapid onset — S. aureus, Bacillus cereus) or by infection (longer incubation — Salmonella, Campylobacter).

Epidemiology

Gastroenteritis is extremely common — norovirus alone causes approximately 3 million cases per year in the UK, with major winter outbreaks in hospitals and care homes. Campylobacter is the most common bacterial cause of gastroenteritis in the UK (~60,000 laboratory-confirmed cases per year). Rotavirus vaccination (introduced 2013) has dramatically reduced childhood rotavirus hospitalisations.

Clinical Features

Symptoms

Diarrhoea — watery (viral/toxin) or bloody (invasive bacterial)

Vomiting — prominent in norovirus and S. aureus food poisoning

Abdominal cramps and pain

Fever (suggests invasive bacterial infection)

Bloody diarrhoea with mucus (dysentery) — Campylobacter, Shigella, E. coli O157, Salmonella

Dehydration signs: thirst, reduced urine output, dizziness

Signs

Signs of dehydration: dry mucous membranes, reduced skin turgor, tachycardia, hypotension

Abdominal tenderness (usually diffuse)

Fever

Investigations

First-line

Stool MC&SSend if: bloody diarrhoea, severe/prolonged (>7 days), immunocompromised, recent overseas travel, recent hospitalisation/antibiotics (request C. diff toxin), suspected outbreak. Identifies Campylobacter, Salmonella, Shigella, E. coli O157

Stool for C. difficile toxinIf recent antibiotic use, hospitalisation, or PPI use — loose stool only

Second-line

U&EsIf clinically dehydrated — assess for AKI and electrolyte disturbance

Stool for ova, cysts, and parasitesIf travel to tropical area — Giardia, Entamoeba, Cryptosporidium

Blood culturesIf systemically unwell, septic, or immunocompromised

Specialist

FBC for HUS screenIf E. coli O157 confirmed or suspected: monitor for HUS (MAHA + thrombocytopenia + AKI). Check FBC, film for schistocytes, LDH, creatinine

Management

NICE CG84 (Diarrhoea and Vomiting in Children) + NICE CKS

Fluid replacement — the cornerstone of treatment

Oral rehydration solution (ORS) for mild-moderate dehydration — particularly important in children and elderly
IV fluids (0.9% NaCl) if unable to tolerate oral, severe dehydration, or haemodynamic instability
Continue breastfeeding in infants
Avoid sugary drinks, fruit juice (osmotic diarrhoea)

Antibiotics — NOT routinely indicated

Most gastroenteritis is self-limiting and antibiotics are NOT needed
Antibiotics indicated for: severe Campylobacter (clarithromycin), invasive Salmonella/bacteraemia (ciprofloxacin), Shigella (ciprofloxacin/azithromycin), travellers diarrhoea with systemic features
E. coli O157: Do NOT give antibiotics — may increase risk of HUS (toxin release from dying bacteria)
Avoid loperamide in bloody diarrhoea, children <12, or suspected E. coli O157

Infection control and public health

Hand hygiene (soap and water — not just alcohol gel for norovirus and C. diff)
Isolate inpatients with suspected infectious diarrhoea
Food handlers, healthcare workers: exclude from work until 48 hours after last episode of D&V
Notify HPT for notifiable organisms: Campylobacter, Salmonella, Shigella, E. coli O157

Complications

Dehydration: The most common complication — can cause AKI, electrolyte disturbance. Major risk in children and elderly
HUS (haemolytic uraemic syndrome): Especially E. coli O157 in children — MAHA + thrombocytopenia + AKI. Leading cause of paediatric AKI in UK
Reactive arthritis: Post-infectious (Campylobacter, Salmonella, Shigella, Yersinia) — sterile arthritis weeks after infection. HLA-B27 associated
Guillain-Barré syndrome: Post-Campylobacter infection (most common preceding infection for GBS)
Toxic megacolon: Rare complication of severe colitis (C. diff, Shigella)

UKMLA Exam Tips

1Campylobacter = most common bacterial cause of gastroenteritis in UK. Associated with Guillain-Barré and reactive arthritis
2E. coli O157 + bloody diarrhoea → do NOT give antibiotics (increases HUS risk). Monitor for HUS (schistocytes + low platelets + AKI)
3Preformed toxin = short incubation (<6 hours): S. aureus (vomiting-predominant), Bacillus cereus (rice — vomiting type; meat — diarrhoea type)
4Norovirus: PCR testing in outbreaks. Highly contagious, short-lived, vomiting-predominant. Alcohol gel NOT effective — use soap and water
5Post-Campylobacter GBS: ascending flaccid paralysis 1-3 weeks after diarrhoeal illness — classic exam scenario
6Rotavirus vaccine given orally at 8 and 12 weeks — part of UK childhood schedule since 2013

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