acute diarrhoea in adults: assessment, dehydration, stool tests, and antibiotics (when needed)

Most adult acute diarrhoea is self-limiting viral gastroenteritis. The main job is to identify dehydration and red flags, support with oral rehydration, and test/treat selectively (especially in bloody diarrhoea, severe systemic illness, immunocompromise, or suspected C. difficile).

• Signs of severe dehydration: confusion, oliguria, hypotension, tachycardia, postural drop, severe weakness.
• Blood in stool, high fever, severe abdominal pain/guarding, or suspected sepsis.
• Immunocompromised patients, frail older adults, significant comorbidity.
• Recent antibiotics or hospital stay (consider C. difficile).

• Fluids: small frequent sips; oral rehydration solution (ORS) if high output.
• Diet: light foods as tolerated; avoid excessive alcohol; continue normal diet when able.
• Antimotility: loperamide can help in non-bloody diarrhoea without fever (avoid in suspected dysentery/C. diff). Typical adult dosing: 4 mg initially, then 2 mg after each loose stool (max 16 mg/day).
• Infection control: handwashing with soap and water; exclude from work (especially food handlers/healthcare) per local public health advice.

• Stool culture/PCR if: bloody diarrhoea, persistent >7 days, severe systemic illness, travel-associated diarrhoea, immunocompromise, outbreak settings.
• C. difficile testing if recent antibiotics/hospital exposure and compatible symptoms.
• Antibiotics: generally not needed; consider only in select scenarios (severe traveller’s diarrhoea, suspected cholera, severe systemic illness) and follow local antimicrobial guidance.

Safety-net: return urgently if unable to keep fluids down, blood appears, fever persists, symptoms worsen, or diarrhoea continues beyond ~7 days.