Infectious Disease

Infectious gastroenteritis

Acute infectious diarrhoea with or without vomiting, managed by prioritising hydration and sepsis assessment, testing selectively, avoiding harmful antibiotics in STEC, and controlling transmission and public-health risk.

In a nutshell

Infectious gastroenteritis usually causes acute diarrhoea with or without vomiting and is managed supportively. First assess dehydration, perfusion, sepsis and an acute abdomen; use oral rehydration when possible, test stool selectively, avoid antibiotics and antimotility drugs in suspected STEC, and involve UKHSA for notifiable infections or outbreaks.

Classic presentation

Sudden diarrhoea with vomiting, abdominal cramps and sometimes fever after food, travel or sick contact. Watery diarrhoea with prominent vomiting suggests viral illness, while fever, severe pain, blood or mucus suggests inflammatory or invasive disease and changes the testing and escalation threshold.

Key points

Dehydration, acute kidney injury and sepsis are the immediate threats; assess perfusion and urine output before focusing on the organism.
Oral rehydration solution and continued age-appropriate feeding are first-line when oral intake is possible; use monitored intravenous fluids for shock, severe dehydration or failure of oral therapy.
Most uncomplicated gastroenteritis does not need antibiotics or stool testing.
Send stool microbiology for bloody or persistent diarrhoea, systemic illness, high-risk hosts, relevant travel or healthcare exposure, suspected outbreak or public-health request.
Avoid antibiotics and antimotility agents when Shiga-toxin-producing E. coli is suspected because of haemolytic uraemic syndrome risk.
Reduced urine output, pallor, bruising, oedema or neurological change after diarrhoea should trigger assessment for HUS.
Wash hands with soap and water, clean contaminated surfaces and exclude from work, school or nursery until 48 hours after the last episode; follow longer organism-specific rules where required.
Notify or discuss notifiable organisms, STEC, clusters and outbreaks with the current UKHSA pathway.

First-line investigation

Clinical hydration and sepsis assessment; send selective stool microbiology for bloody, persistent, systemic, high-risk, travel-related or outbreak-associated illness rather than testing every self-limiting case.

Management

Assess perfusion, sepsis and the abdomen

Assess hydration, urine output, observations, mental state and abdominal signs; escalate shock, sepsis, severe pain, distension or suspected HUS immediately.^3,4,5

Rehydrate and provide supportive care

Use oral rehydration solution and small frequent sips when possible, continue appropriate feeding, and use monitored intravenous fluids when oral replacement fails or there is shock or severe dehydration.^3,4,2

Test selectively and treat the cause

Send stool testing for bloody, persistent, systemic, high-risk, travel-related or outbreak-associated illness; reserve antibiotics for specific indications and avoid them in suspected STEC unless specialist advice supports treatment.^1,5,3

Stop transmission

Use soap-and-water handwashing, environmental cleaning, safe food handling and 48-hour exclusion after symptoms; use organism-specific and setting-specific advice for food handlers, healthcare and childcare.^1,2

Escalate STEC, HUS and outbreaks

Involve the UKHSA health protection team for STEC, notifiable organisms, clusters and outbreaks; monitor renal function, platelets and haemolysis when HUS is possible and involve renal or infectious-disease specialists.^5,6,7

Safety-net and reconsider the diagnosis

Give return advice for worsening dehydration, reduced urine, blood, severe pain, confusion, persistent vomiting or non-resolving diarrhoea; reconsider C. difficile, IBD, coeliac disease, medication effects or an acute abdomen when recovery is atypical.^2,8,1

Exam traps

Do not give antibiotics or antimotility agents reflexively in suspected STEC; HUS is the key complication.
Blood in stool, severe pain or sepsis is not a routine viral-gastroenteritis presentation and needs investigation and escalation.
A stool pathogen result does not remove the need to assess hydration, renal function and alternative diagnoses.
Recent antibiotics or healthcare exposure should prompt consideration of C. difficile, with its own testing pathway.
Alcohol gel alone is not a substitute for soap-and-water handwashing in outbreaks where norovirus or other enteric infection is suspected.
Do not miss an acute abdomen, diabetic ketoacidosis, inflammatory bowel disease or medication-related diarrhoea when the course is atypical.

Illustrations

Secretory versus invasive mechanismsDiagram contrasting toxin-mediated fluid secretion with mucosal invasion and inflammation in infectious gastroenteritis.PassFinals · original

Watery versus inflammatory stool patternsClinical teaching image contrasting profuse watery diarrhoea with bloody or mucoid dysentery; the image should not be used alone to identify a pathogen.F1jmm, Wikimedia Commons · CC-BY-SA-3.0

Oral rehydration therapyIllustration of oral rehydration solution use and small frequent fluid intake for diarrhoeal illness.PassFinals · original

Key sources

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.