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Acute diarrhoea in adults
Most acute diarrhoea is viral and self-limiting; the main treatment is fluids, and stool testing and antibiotics are kept for patients with blood, high fever, severe dehydration, more than a week's duration, immunosuppression, or recent hospital stay and antibiotics.
Why it matters in the exam
The exam asks "in which cases should Salmonella infection be treated with antibiotics?", which patient with watery diarrhoea needs a work-up, and what to do about prolonged watery diarrhoea in an older woman who smokes (microscopic colitis). Other questions test the danger of antibiotics in bloody diarrhoea without fever (Shiga toxin-producing E. coli).
Remember that in non-invasive Salmonella in a healthy person antibiotics do not shorten the illness and prolong carriage, while patients over 50 with atherosclerosis or vascular grafts, immunosuppressed patients and young infants are treated.
Acute diarrhoea is one of the most common complaints in the clinic, and most patients mainly need an explanation about fluids and warning signs.
Diarrhoea in a nursing home or after a shared meal also raises the question of notifying the Ministry of Health and of isolation. Further questions deal with travellers' diarrhoea and when azithromycin is appropriate.
Key points
- Most diarrhoea is viral; the treatment is fluids.
- Tests only with blood, high fever, dehydration, duration over a week or immunosuppression.
- Salmonella in a healthy person — no antibiotics; in risk groups — yes.
- Bloody diarrhoea without fever — no antibiotics and no loperamide.
- Prolonged watery diarrhoea in an older woman — microscopic colitis, biopsies.
Summary table
| Condition | Clues | Work-up | Treatment |
|---|---|---|---|
| Viral diarrhoea | Watery, vomiting, family outbreak, 1–3 days | No tests | Fluids and oral rehydration solution; loperamide when there is no blood or high fever |
| Salmonella | Fever, diarrhoea, food (eggs, chicken) | Stool culture when risk signs are present | In a healthy person — no antibiotics; over 50 with atherosclerosis or grafts, immunosuppressed, infant under 3 months — yes |
| Bloody diarrhoea without fever | Suspected Shiga toxin-producing E. coli | Culture and toxin test | No antibiotics and no loperamide — risk of HUS |
| Febrile dysentery (Shigella, Campylobacter) | Blood, fever, pain | Stool culture | Azithromycin |
| Clostridioides difficile | Recent antibiotics or hospital stay | Toxin test | Oral vancomycin or fidaxomicin; stop the causative antibiotic |
| Microscopic colitis | Prolonged watery diarrhoea in an older woman; smoking, NSAIDs, PPIs, SSRIs | Colonoscopy with biopsies (normal appearance) | Budesonide and stopping causative drugs |
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Sources
- Infectious Diseases Society of America, 2017 — Clinical practice guidelines for the diagnosis and management of infectious diarrhea
- American College of Gastroenterology, 2016 — Clinical guideline: diagnosis, treatment, and prevention of acute diarrheal infections in adults
- Goroll AH, Mulley AG. Primary Care Medicine, 8th edition (2020) — Approach to the patient with acute diarrhea
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-06. The text may contain errors; when in doubt, check the source.