USMLE Prep - Medical Reference Library

Clostridioides difficile Infection — Adult

System: Infectious Diseases • Reviewed: Aug 31, 2025 • Step 1Step 2Step 3

Synopsis:

Test only patients with unexplained new diarrhea; use toxin-based algorithm; treat with fidaxomicin (preferred) or oral vancomycin; consider bezlotoxumab and FMT for recurrences.

Key Points

  • Stabilize ABCs; begin targeted evaluation without delaying life-saving therapy.
  • Use system-specific risk tools to guide testing and disposition.
  • Order high-yield tests first; escalate imaging when indicated.
  • Start evidence-based initial therapy and reassess frequently.

Algorithm

  1. Primary survey and vitals; IV access and monitors.
  2. Focused history/physical; identify red flags and likely etiologies.
  3. Order system-appropriate labs and imaging (see Investigations).
  4. Initiate guideline-based empiric therapy (see Pharmacology).
  5. Reassess response; arrange consultation and definitive management.

Clinical Synopsis & Reasoning

For Clostridioides Difficile Infection Adult, frame the differential by acuity and pathophysiology, then align diagnostics to the leading hypotheses. Prioritize stabilization while obtaining high‑yield studies such as CBC (Inflammation/infection), Lactate (Hypoperfusion), Blood cultures (Pathogen ID). Incorporate bedside imaging and targeted labs to define severity and identify complications; synthesize results with clinical trajectory to refine the working diagnosis and disposition needs.


Treatment Strategy & Disposition

Initiate disease‑directed therapy alongside supportive care, titrating to objective response. Pharmacologic options commonly include Broad-spectrum antibiotics. Use validated frameworks (e.g., Severity (Typical Adult Criteria)) to guide escalation and site of care. Address precipitating factors, de‑escalate empiric therapies with data, and arrange follow‑up for monitoring and risk‑factor modification; admit patients with instability, high risk of deterioration, or needs for close monitoring.


Epidemiology / Risk Factors

  • Immunosuppression, devices; recent hospitalization

Investigations

TestRole / RationaleTypical FindingsNotes
CBCInflammation/infectionLeukocytosis/leukopenia
LactateHypoperfusionElevatedTrend
Blood culturesPathogen IDPositive/negativeBefore antibiotics if feasible

Severity (Typical Adult Criteria)

CategoryFeatures
NonsevereWBC ≤15,000 and creatinine <1.5 × baseline
SevereWBC >15,000 or creatinine ≥1.5 × baseline
FulminantHypotension, shock, ileus, megacolon

Pharmacology

MedicationMechanismOnsetRole in TherapyLimitations
Oral vancomycinCell-wall inhibitionHoursNon-fulminant CDINephrotoxicity minimal (PO)
FidaxomicinMacrocyclic antibioticHoursAlternative first-lineCost
IV metronidazole (add)DNA damageHoursFulminant disease adjunctDisulfiram-like reaction

Prognosis / Complications

  • Depends on host and source control; sepsis/organ failure risk

Patient Education / Counseling

  • Explain red flags and when to seek emergent care.
  • Reinforce medication adherence and follow-up plan.

Notes

Ensure stewardship: avoid PPIs and unnecessary antibiotics. Private rooms and hand hygiene with soap and water reduce transmission.


References

  1. IDSA/SHEA CDI Guideline — Link
  2. CDC — C. diff — Link