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Clostridioides difficile infection
New diarrhoea after antibiotics or admission is C. difficile until proven otherwise; it is treated with fidaxomicin or oral vancomycin — not intravenous vancomycin — and graded as non-severe, severe or fulminant.
Why it matters in the exam
The typical question presents an older inpatient who received a cephalosporin, clindamycin or a quinolone and developed 3 or more loose stools a day, abdominal pain and fever. The test (GDH antigen and toxin, or PCR) is sent only when there is diarrhoea — not on formed stool and not "as a test of cure". Severity is set in the laboratory: white cells of 15,000 or more or creatinine above 1.5 mg/dL = severe disease; low blood pressure, shock, ileus or megacolon = fulminant disease.
In treatment: fidaxomicin 200 mg twice a day for 10 days (preferred, fewer recurrences) or oral vancomycin 125 mg four times a day for 10 days; metronidazole only when both are unavailable and the disease is not severe. In fulminant disease: vancomycin 500 mg four times a day by mouth or tube, rectal vancomycin if there is ileus, intravenous metronidazole, and a surgical consultation. For recurrence — fidaxomicin or a tapering course of vancomycin; after 2 or more recurrences — faecal microbiota transplantation (FMT). Prevention: stop the triggering antibiotic, contact isolation and handwashing with soap and water, because alcohol does not kill the spores.
Key points
- Diarrhoea after antibiotics or admission → test for C. difficile.
- Severe: white cells 15,000 or more or creatinine above 1.5 mg/dL.
- Treatment: fidaxomicin or oral vancomycin for 10 days.
- Fulminant: oral and rectal vancomycin 500 mg + intravenous metronidazole + a surgeon.
- 2 or more recurrences → FMT; hands with soap and water.
Summary table
| Severity | Criterion | Treatment | Exam note |
|---|---|---|---|
| Non-severe | White cells below 15,000 and creatinine up to 1.5 mg/dL | Fidaxomicin 200 mg twice a day for 10 days, or oral vancomycin 125 mg four times a day | Metronidazole only if no alternative |
| Severe | White cells 15,000 or more or creatinine above 1.5 mg/dL | Fidaxomicin or oral vancomycin | Not metronidazole |
| Fulminant | Shock, ileus, megacolon | Vancomycin 500 mg four times a day + rectal + intravenous metronidazole | Surgical consultation |
| First recurrence | Return within 8 weeks | Fidaxomicin or tapering vancomycin | Consider bezlotoxumab |
| Repeated recurrences | 2 or more recurrences | Faecal microbiota transplantation (FMT) | Highly effective |
| Prevention | Every patient | Stop the antibiotic, contact isolation, soap and water | Alcohol does not kill spores |
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Sources
- IDSA/SHEA Focused Update Guideline on Management of Clostridioides difficile Infection in Adults, 2021 — Fidaxomicin, vancomycin, bezlotoxumab and recurrence
- Harrison's Principles of Internal Medicine, 21st edition (2022) — Clostridioides difficile Infection, Including Pseudomembranous Colitis
Sources are given for further reading; the text is written afresh and not copied from them.
Reviewed by the Examqo AI Professor · 2026-11-02. The text may contain errors; when in doubt, check the source.