Diagnostic assessment of C. difficile infection

The diagnosis of Clostridioides difficile infection is based on clinical features suggestive of C. difficile infection (diarrhoea; clinical or radiological evidence of an ileus or toxic megacolon) and either:

  • microbiological evidence of toxin-producing C. difficile in stools, or
  • colonoscopy findings or histopathology results that demonstrate pseudomembranous colitis.

For indications to test for C. difficile, see Faecal testing for infectious diarrhoea. Perform testing for C. difficile or its toxins on unformed stool only, unless the patient has ileus.

Consider empirical therapy for C. difficile infection in adults with features of severe, complicated, or fulminant disease, particularly in those who have used an antibiotic or stayed in a healthcare setting in the past 90 days, or have a history of C. difficile infection in the past 60 daysMcDonald, 2018. Empirical therapy for C. difficile infection is rarely indicated for children; it should only be considered with expert advice if prompt testing is not possible and severe, complicated or fulminant infection is suspected (eg toxic megacolon).

Note: Always correlate clinical symptoms with test results when deciding whether to treat a person with a positive C. difficile result.

Various sequential testing algorithms for C. difficile infection are used by laboratories and results of these tests are issued with interpretative comments to aid clinical decision making. When reviewing these results, consider the following principles:

  • Always correlate clinical symptoms with test results when deciding whether treatment is indicated. Test results can be positive in asymptomatic carriers of toxigenic C. difficile, and in the weeks following recovery after an episode of C. difficile diarrhoea; these patients do not require treatment.
  • Review a positive result in a young child carefully because colonisation with C. difficile is common in young children, particularly in those up to 2 years of age. C. difficile may not be the cause of disease and treatment may not be necessary.
  • Do not repeat testing during the same episode of diarrhoea, or test for cure.

Consult with a clinical microbiologist or infectious diseases physician if further guidance on interpreting C. difficile test results is required.