Diarrhoea usually begins within 4–10 days of antibiotic treatment, but may not appear for 4–6 weeks.

Presentations range from mild self-limiting watery diarrhoea to (rarely) acute fulminating toxic megacolon.

Low-grade fever and abdominal tenderness are common.

Although the rectum and sigmoid colon are usually involved, in 10% of cases colitis is confined to the more proximal colon.

Diagnosis is based on detection of C. difficile toxins A and B in the stool. In severe colitis, sigmoidoscopy may show adherent yellow plaques (2–10 mm in diameter).

Supportive treatment and isolation of the patient to reduce the risk of spread.

Stop antibiotic therapy if possible. If diarrhoea mild (1–2stools daily), symptoms may resolve within 1–2 weeks without further treatment.

Refer to local treatment guidelines. In general, if moderate diarrhoea (three or more stools daily), give metronidazole 400 mg 8-hourly PO for 7–10 days. If severe infection (usually associated with hypoalbuminaemia), give vancomycin 125 mg 6-hourly PO.

Around 20% of patients will have a relapse after completing a course of metronidazole, due to germination of residual spores within the colon, re-infection with C. difficile or further antibiotic treatment: give either a further course of metronidazole or vancomycin 125 mg 6-hourly PO for 7–10 days.

If the patient is severely ill and unable to take oral medication, give metronidazole 500 mg 8-hourly IV (IV vancomycin should not be used as significant excretion into the gut does not occur).