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. The clinical task in primary care is not to chase a microbiological diagnosis in every case, but to spot the dehydrated or septic patient, recognise the red flags, and resist the urge to prescribe antibiotics.
Duration drives the differential. The single most useful first step is to place the illness into one of three bands, because 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, or 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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