GPAtlas🧭 When to suspect
Diarrhoea is the passage of loose or watery stools three or more times in 24 hours, or more frequently than is normal for that person.
Most acute episodes are infectious and self-limiting – the great majority are viral, settle within a week, and need nothing more than fluids and safety-netting.
Do not chase a microbiological diagnosis in every case. Instead:
• Spot the dehydrated or septic patient.
• Recognise the red flags.
• Resist the urge to prescribe antibiotics.
Duration drives the differential. Start by placing the illness in one of three bands: each points to a different cause and a different threshold for investigation.
| Category | Duration | Implication |
|---|---|---|
| Acute | < 14 days | • Usually infectious (most often viral) and self-limiting • Supportive care |
| Persistent | 14–28 days | • Consider parasitic and post-infectious causes • Begin investigation |
| Chronic | > 4 weeks | • Non-infectious causes more likely (IBD, coeliac, malignancy, functional) • Structured work-up |
Raise your index of suspicion for a serious or specific cause with:
• Blood or mucus in the stool.
• High fever or systemic illness.
• Recent antibiotics or hospital admission (Clostridioides difficile).
• Foreign travel.
• Contact with farm animals or an unwell contact.
• Immunosuppression.
Always consider whether loose stool is in fact overflow around faecal impaction in a frail or constipated patient.
Source: NICE · UK Health Security Agency · British Society of Gastroenterology
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