Acute Infectious Diarrhoea (Gastroenteritis)

Condition

Diarrhoea lasting less than 14 days. Causes: viral (norovirus, adenovirus, astrovirus, rotavirus); toxin-mediated; bacterial; protozoal/parasitic. Most cases are self-limiting and resolve without specific treatment.

History features by likely cause

Viral: contact with someone with similar symptoms; prominent upper GI symptoms; resolves in 24–48 hours.

Bacterial: fever, tenesmus (urgency with minimal output), blood in stool; returned travellers; sometimes recent antibiotic use (C. difficile).

Toxin-mediated: rapid onset (hours), closely clustered cases; prominent vomiting/abdominal pain.

Severity: mild (able to undertake usual activities); moderate (modification of normal activities); severe (incapacitation, may need admission).

Examination

Assess hydration status. Features suggesting a need for microbiological testing: high fever; tachycardia; abdominal tenderness/severe abdominal pain; high-volume diarrhoea with hypovolaemia; blood in stool; prolonged symptoms; leucocytosis.

Investigations

Stool culture and PCR + C. difficile toxin if: bloody stools, moderate-to-severe disease, or prolonged symptoms; immunocompromised patients; public health importance (food handlers, RACF residents, outbreaks).

Management

Rehydration — oral is ideal, unless there’s severe dehydration.

Antibiotic therapy: not usually required for community-acquired infectious diarrhoea. Contraindicated in children with bloody diarrhoea without fever or sepsis, due to the risk of haemolytic uraemic syndrome from enterohaemorrhagic E. coli.

Consider antibiotics for: returned travellers (shortens illness by 1–3 days); severe disease; immunocompromised patients. If using antibiotics, do a stool culture first, then ciprofloxacin 500mg twice daily for 3 days.

Clostridium difficile infection

The most severe antibiotic-associated diarrhoea — infection can occur during, or some months after, a course of antibiotics.

Risk factors: exposure to broad-spectrum antibiotics; hospitalisation; chemotherapy; PPIs.

History: diarrhoea; recent broad-spectrum antibiotic use; recent hospitalisation.

Investigations: C. difficile toxin or culture.

Management — mild-moderate disease: oral vancomycin 125mg four times daily for 10 days, or fidaxomicin, are now preferred — see the guideline update below. Metronidazole is reserved as an alternative only when vancomycin/fidaxomicin are unavailable.