Clostridioides difficile

• Is a bacteria that causes disease by producing a toxin in the bowel.
• Causes diarrhoea, particularly in people who have recently received antibiotic treatment.
• Other risk factors include advanced age, hospitalisation and comorbid illnesses.

A small proportion of people carry C. difficile in their bowel under normal circumstances. This proportion goes up in people who have been hospitalised and in young children.

Test people with unexplained (e.g. not just due to laxatives, enteral feeding) diarrhoea that occurs in hospital, or in other people who have risk factors and persistent diarrhoea.

Request C. diff stool testing (must be liquid/take shape of the container)

• Many laboratories use a two-step protocol
• Step 1: test for presence of organism in the stool: GDH antigen or PCR/NAAT
  • Good sensitivity – a negative test makes the diagnosis unlikely
  • Reasonable specificity – a positive test confirms presence of the organism, but does not necessarily imply toxin production/disease
• Step 2: test for presence of toxin in the stool: toxin enzyme immunoassay (EIA)
  • Reasonable sensitivity – a negative test makes the diagnosis less likely, but cannot exclude it.
  • Good specificity – a positive test makes the diagnosis likely in the appropriate clinical context
  • To enhance the sensitivity of toxin detection, our laboratory performs toxigenic culture on stools that test positive for GDH antigen, but negative for toxin EIA.
    • Stools are cultured for 48h to grow C.diff. The cultures are then tested directly with a toxin EIA to detect toxin production.
• Note, most PCR/NAAT tests detect the specific gene that produces toxin. This tells you that the organism is capable of producing the toxin, but does not necessarily tell you it has switched on toxin production (which is what causes disease).
  • Some labs use PCR/NAAT as a standalone test, however we favour a separate test to look for toxin in stool, which increases the overall specificity of the testing process.

• Test of cure:
  • This is not recommended, as many patients will remain positive on testing, even with successful treatment. Resolution of diarrhoea is the goal of treatment.
• Testing in young children:
  • This should only be done under specialist guidance, as children less than 3 years of age will often have a positive test, even if C.diff is not the cause of their symptoms.