Acute infectious diarrhoea — Rapid

Synopsis

Assess acute diarrhoea by physiological severity and exposure, correct fluid and electrolyte loss, obtain targeted stool microbiology and avoid antimicrobials or antimotility drugs when they increase harm.

First decide whether the patient has shock, severe dehydration, sepsis or an acute surgical abdomen; organism naming comes later.
Use oral rehydration solution for most conscious patients, replacing sodium and glucose together rather than relying on plain water.
In adult shock give 500 mL crystalloid containing sodium 130 to 154 mmol/L over less than 15 minutes, then reassess before further boluses.
Request stool testing for blood, severe or prolonged illness, immunosuppression, travel, recent antibiotics, healthcare exposure or a possible outbreak.
Take blood cultures before antibiotics in systemic sepsis, enteric fever risk or suspected invasive infection.
Do not prescribe antibiotics routinely: most community gastroenteritis is self-limiting and treatment can prolong carriage or worsen STEC outcomes.
Avoid loperamide and other antimotility drugs in bloody diarrhoea, suspected STEC, C difficile, high fever or toxic colitis.
Use contact precautions, soap-and-water hand hygiene and safe food handling; alcohol gel alone is unreliable against some enteric pathogens and spores.

Key red flags

Shock, altered mental state, weak pulse, prolonged capillary refill or minimal urine output indicates severe intravascular depletion or sepsis.

Peritonism, marked distension, ileus or systemic toxicity can indicate perforation, toxic megacolon or surgical abdominal disease.

Bloody diarrhoea with falling platelets, anaemia or rising creatinine suggests STEC-associated haemolytic uraemic syndrome.

Recent antibiotics, healthcare exposure or care-home residence increases Clostridioides difficile and outbreak risk.

Severe illness in pregnancy, older age, immunosuppression or major comorbidity needs a lower admission and testing threshold.

Multiple linked cases, food-handler illness, healthcare work or recent institutional exposure requires urgent infection-control and public-health action.

Inflammatory dysentery

Blood, mucus, fever, tenesmus and lower abdominal pain suggest colonic invasion or toxin injury and require stool testing.

Severe dehydration

Thirst, dry mucosa, tachycardia, postural hypotension, reduced urine, confusion and cool peripheries mark progressive fluid loss.

Healthcare-associated diarrhoea

Recent antibiotics, hospital stay, care facility or household healthcare exposure raises C difficile and outbreak-control priorities.

Outbreak pattern

Similar illness among household, ward, care-home, nursery or food-event contacts suggests a common source and prompts early reporting.

Investigation priorities

Stool PCR or culture panelFirst step

Identify bacterial and selected viral pathogens in severe, bloody, persistent, imported or outbreak-associated diarrhoea.

Management branches

TRIAGEGrade severity before aetiology

An adult presents with acute diarrhoea or vomiting.

Check airway, breathing, circulation, mental state, capillary refill, postural symptoms and urine output and examine for peritonism or distension.
Identify pregnancy, frailty, immune compromise, renal or cardiac disease and medicines that increase dehydration or acute kidney injury risk.
Isolate suspected infectious diarrhoea and take a concise exposure history including travel, antibiotics, healthcare and linked cases.
Admit urgently for shock, severe dehydration, sepsis, inability to retain fluid, significant bleeding or abdominal complication.

Key medicines

Oral rehydration solutionGive frequent small volumes prepared exactly to the product instructions, increasing intake to replace each loose stool and continuing as tolerated.Do not over-dilute or concentrate sachets; vomiting is managed with slower repeated sips, while shock or impaired consciousness requires intravenous treatment.

Intravenous crystalloid for shockGive 500 mL crystalloid containing sodium 130 to 154 mmol/L over less than 15 minutes in an adult, then reassess before repeating.Use smaller boluses and close lung, perfusion and urine monitoring in cardiac or renal impairment; ongoing haemorrhage needs blood-product strategy.

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