Clostridioides Difficile Infection (CDI)
Clostridioides difficile infection (CDI) is defined as:
- 3 or more episodes of loose stool within 24hrs i.e. Bristol stool chart types 5-7 and
- Diarrhoea that is not attributable to any other cause or therapy, including medicines such as laxatives and
- The presence of a positive toxin assay and/or endoscopic evidence of pseudo-membranous colitis.
Laboratory diagnosis C. difficile has been updated from 5th May 2026 to use C. difficile toxin PCR as the first-line screening test rather than GDH – if positive, a C. difficile toxin antigen will be done to confirm active C. difficile infection (CDI). See additional information section at the end of guidance for more details about the test.
Below is a table summarising interpretation of C. difficile lab results:
| Toxin PCR | Toxin antigen | Interpretation | Minimum re-test interval (days) |
| Positive | Positive | Consistent with CDI – treat as per this guideline. | 28 |
| Positive | Negative | Colonised with toxigenic C. difficile. Potential to develop into CDI and to transmit to other patients. Isolate patient in a side room. If symptoms consistent with C. difficile treat as per CDI. | 28 |
| Negative | Not tested | CDI highly unlikely. Consider another cause for diarrhoea. | 7 |
Always assess the severity of CDI:
Life-threatening CDI includes hypotension non-responsive to fluid filling, partial or complete ileus or toxic megacolon, or CT evidence of severe disease or bowel perforation.
Severe CDI is associated with:
- Acute abdomen: Ileus, peritonitis, perforation
- Temperature over 38.5°C
- White Cell Count (WCC) of 15 x109/L or greater
- Acutely rising serum creatinine (more than 50% increase above baseline)
- Imaging: megacolon, colonic wall thickening, pericolonic fat stranding
Moderate CDI is associated with a raised WCC that is less than 15x109/L. Typically associated with 3–5 stools per day.
Mild CDI is not associated with a raised WCC. Typically associated with less than 3 stools of type 5–7 on the Bristol Stool Chart per day.
Empirical treatment of suspected or confirmed CDI: mild, moderate or severe disease
- Consider IV fluids and electrolyte correction.
- Maintain stool chart.
- For severe disease, refer to Micro/ID and gastroenterology.
- Treat for 10 days
First line: vancomycin 125mg po qds for 10 days
- If the patient fails to respond to vancomycin after 7 days, consult Micro/ID who may advise to switch to fidaxomicin 200mg bd for 10 days.
- Use clinical judgement to determine whether antibiotic treatment for C. difficile is ineffective. It is not usually possible to determine this until day 7 because diarrhoea may take 1 to 2 weeks to resolve.
- For patients with enteral feeding tube or swallowing difficulties order vancomycin liquid or fidaxomicin liquid from pharmacy.
Empirical treatment of suspected or confirmed CDI: life-threatening
Urgent referral to gastroenterology on-call doctor and Micro/ID
- Supportive measures: resuscitate patient with IV fluids and correct electrolytes
- Commence/maintain stool chart
- Abdominal imaging
*When patient is able to tolerate oral medication the metronidazole can be changed to metronidazole 400mg po tds.
- Always discuss treatment of life-threatening cases with Micro/ID as broad-spectrum antibiotics may also be indicated if another condition is being treated.
- If the patient fails to respond to vancomycin and metronidazole after 7 days, consult Micro/ID who may advise to switch to fidaxomicin 200mg bd for 10 days.
- Use clinical judgement to determine whether antibiotic treatment for C. difficile is ineffective. It is not usually possible to determine this until day 7 because diarrhoea may take 1 to 2 weeks to resolve.
- For patients with enteral feeding tube or swallowing difficulties order vancomycin liquid or fidaxomicin liquid from pharmacy.
Relapse
Relapse of CDI symptoms within 12 weeks of initial treatment (with positive CDT stool test): fidaxomicin 200mg po bd for 10 days
For patients with enteral feeding tube or swallowing difficulties order fidaxomicin liquid from pharmacy.
Recurrence
Recurrent episode of CDI after 12 weeks of initial treatment (with positive CDT stool test): Seek ID Micro / Gastroenterology advice.
Treatment options include:
vancomycin 125 mg po qds for 10 days
OR
fidaxomicin 200 mg po bd for 10 days
For patients with enteral feeding tube or swallowing difficulties order vancomycin liquid or fidaxomicin liquid from pharmacy.
2 or more previous confirmed CDI episodes
Recurrent episode of CDI after 12 weeks of initial treatment (with positive CDT stool test): Seek Micro/ID and Gastroenterology advice.
Consider Faecal Matter Transplant (FMT, IPG485) or tapering vancomycin (as below)
Tapering vancomycin course:
- 125mg po qds for 10 days, then,
- 125mg po bd for 7 days, then,
- 125mg po od for 7 days, then,
- 125mg po once every 2 or 3 days for 2 to 8 weeks.
For patients with enteral feeding tube or swallowing difficulties order vancomycin liquid from pharmacy.
Additional information
- C. difficile toxin PCR is a screening test for C. difficile carriage but does not confirm C. difficile infection unless the gene is switched on to produce toxin antigen. These strains can live harmlessly in the colon without producing toxin. However, they can transmit to others, hence the requirement, if possible, for side-room isolation. They can also switch to producing toxin and cause CDI, therefore the prescription of antibiotics in patients carrying potentially toxigenic strains must be carefully considered to avoid CDI.
- A positive test for C. difficile toxin antigen confirms CDI.
- Bacteria that are C. difficile toxin PCR negative are not pathogenic.