01Approach to the Critical Patient/attcp44

Fulminant CDI recognition

›Fulminant CDI criteria

›Hypotension or shock (SBP <90 mmHg or MAP <65 mmHg)

›Ileus (abdominal distension without diarrhea)

›Toxic megacolon (colonic dilation >6 cm on imaging)

›Organ failure (AKI, respiratory failure, altered mental status)

›Peritoneal signs indicating colonic perforation

›If any fulminant criterion present, escalate immediately to resuscitation bay

Resuscitation priorities

›Volume resuscitation targets

›IV crystalloid for hemodynamic instability

›Lactated Ringer's preferred over normal saline for large-volume resuscitation

›MAP target ≥65 mmHg

›Urine output target ≥0.5 mL/kg/hour

›Vasopressor support

›Norepinephrine first-line if fluid-refractory shock

›Initiate via central or large peripheral access

›Target MAP ≥65 mmHg

›Sepsis bundle activation

›Blood cultures before antibiotics

›Lactate measurement

›If lactate ≥5 mmol/L, mortality risk significantly elevated

›Class I recommendation: antibiotics within 1 hour of septic shock recognition

Immediate pharmacologic interventions

›Fulminant CDI antibiotic protocol

›Oral vancomycin 500 mg QID (enteral route preferred)

›IV metronidazole 500 mg Q8H (add when oral route unreliable)

›Rectal vancomycin 500 mg in 100 mL NS retention enema Q6H if ileus present

02History/hx49

Core symptoms

›Diarrhea characteristics

›Watery, non-bloody stools (≥3 unformed stools in 24 hours is testing threshold)

›Onset during or within 3 months of antibiotic therapy

›Bloody stool uncommon — if present, consider alternative diagnosis

›Frequency, volume, and duration of episodes

›Associated symptoms

›Abdominal cramping and pain

›Fever (low-grade to high)

›Nausea and anorexia

›Malaise and fatigue

›Alarm features

›Abdominal distension without diarrhea (ileus pattern)

›Severe abdominal pain out of proportion to exam

›Decreased urine output (AKI from dehydration or sepsis)

›Altered mental status (sepsis marker)

Antibiotic exposure history

›Recent antibiotic use

›Any antibiotic within past 3 months (strongest single risk factor)

›High-risk agents: clindamycin, fluoroquinolones, 3rd-generation cephalosporins, carbapenems, ampicillin-clavulanate

›Duration, number of courses, and route of administration

›Outpatient vs inpatient courses

›Current antibiotic use

›Active antibiotic for concurrent infection (guides discontinuation decision)

Healthcare exposure history

›Healthcare facility contact

›Recent hospitalization (within past 3 months)

›Long-term care or nursing home residence

03Physical Exam/exam34

Vital signs and hemodynamic assessment

›Vital sign patterns

›Fever >38.5°C (present in minority of CDI; high fever suggests severe disease)

›Tachycardia (early shock indicator and dehydration marker)

›Hypotension (SBP <90 mmHg — fulminant criterion)

›Tachypnea (sepsis, pain, or metabolic acidosis)

›Volume status assessment

›Dry mucous membranes

›Poor skin turgor

›Delayed capillary refill (>2 seconds)

›Orthostatic vital signs if ambulatory

Abdominal examination

›Inspection

›Distension (ileus or toxic megacolon)

›Visible peristalsis (obstruction)

›Auscultation

›Decreased or absent bowel sounds (ileus)

›High-pitched tinkling sounds (early obstruction)

›Palpation

›Diffuse tenderness (typical in CDI)

›Localized RLQ or LLQ tenderness

›Peritoneal signs: rebound tenderness, guarding, rigidity

›If peritoneal signs present — surgical emergency, mobilize team immediately

›Rectal examination

›Watery stool character (confirms diarrhea)

›Absence of gross blood (bloody stool suggests alternative diagnosis)

›Rectal swab for PCR if patient cannot produce stool (ileus)

04Differential Diagnosis/ddx45

Infectious causes of diarrhea

›Antibiotic-associated diarrhea (non-CDI)

›Accounts for approximately 70% of antibiotic-associated diarrhea

›No toxin production; diagnosis of exclusion after negative CDI testing

›ICD-10: K52.1

›Infectious colitis

›Salmonella, Shigella, Campylobacter — food-borne, more likely bloody diarrhea

›CMV colitis — immunocompromised patients, endoscopic diagnosis

›Enteric fever — systemic prodrome, relative bradycardia

›ICD-10: A09 (unspecified infectious gastroenteritis and colitis)

›Small bowel bacterial overgrowth

›Bloating, flatulence, watery diarrhea

›Risk: prior GI surgery, motility disorders, PPI use

›ICD-10: K63.89

Inflammatory causes

›Inflammatory bowel disease flare

›Ulcerative colitis or Crohn's — can coexist with CDI

›Prior IBD history, rectal bleeding, extraintestinal manifestations

›ICD-10: K50.9, K51.9

›Microscopic colitis

›Chronic watery diarrhea, normal colonoscopy appearance

›More common in older women; NSAID and PPI association

›ICD-10: K52.89

›Ischemic colitis

›Elderly patients with vascular risk factors

›Bloody diarrhea, left-sided abdominal pain

›ICD-10: K55.0

05Laboratory Tests/lt55

Stool diagnostic testing

›CDI stool testing algorithm

›Perform only on unformed/watery stool (≥3 unformed stools in 24 hours)

›Do not test formed stool — high false-positive rate from asymptomatic colonization

›Do not repeat testing within 7 days if NAAT negative

›Do not perform test of cure — shedding persists in 56% of patients up to 4 weeks after successful treatment

›Two-step algorithm (preferred)

›Step 1: GDH antigen or NAAT (high sensitivity screening)

›Step 2: Toxin EIA confirmation (confirms active toxin production)

›NAAT positive + Toxin EIA positive: treat as CDI

›NAAT positive + Toxin EIA negative: likely colonization, consider clinical context

›NAAT (nucleic acid amplification test / PCR)

›High sensitivity and specificity for C. difficile detection

›Cannot distinguish colonization from active infection

›Rectal swab PCR: acceptable when patient with ileus cannot produce stool

›Toxin EIA (enzyme immunoassay)

›Detects toxin A and/or toxin B

›Lower sensitivity than NAAT (75–85%); high specificity

›Positive result confirms active CDI

Severity stratification labs

›Complete blood count with differential

›WBC >15,000/µL → severe CDI criterion

›WBC >35,000/µL → fulminant CDI predictor, elevated mortality

›WBC <4,000/µL → poor prognosis (marrow suppression from severe sepsis)

›Bandemia ≥10% associated with mortality

›Comprehensive metabolic panel

›Creatinine: ≥1.5× baseline → severe CDI criterion

›BUN: elevated with dehydration and AKI

06Diagnostic Tests/dt65

Scoring Systems

›IDSA/SHEA severity classification (2021)

›Nonsevere: WBC ≤15,000/µL AND creatinine <1.5× baseline

›Severe: WBC >15,000/µL OR creatinine ≥1.5× baseline

›Fulminant: hypotension, shock, ileus, megacolon, or organ failure

›Guides initial antibiotic selection and disposition

›ATLAS score (validated bedside scoring)

›Components: Age, Treatment with systemic antibiotics, Leukocyte count, Albumin, creatinine (Serum)

›Predicts treatment response and cure

›Score 0–7; higher scores associated with treatment failure

›Clinically useful for identifying patients at risk for complicated course

›CDI recurrence risk factors

›First recurrence rate: ~20% after initial episode

›Second recurrence rate: ~40%

›Third or subsequent recurrence rate: up to 60%

›Risk factors: age ≥65, continued antibiotic use, PPI use, prior recurrences, immunosuppression

MRI

›MRI abdomen in CDI

›Not routinely indicated for CDI diagnosis or severity assessment

›Limited availability in acute setting limits utility

›May be considered for patients with contraindication to CT contrast

›MRI findings in colitis (general)

›Colonic wall thickening on T2-weighted sequences

›Pericolic fat stranding

›Mucosal enhancement on post-contrast sequences

›Inferior to CT for detection of perforation and pneumoperitoneum

CT

›CT abdomen and pelvis indications

07Disposition/dispo37

ICU admission criteria

›ICU-level care indications

›Fulminant CDI with hemodynamic instability

›Vasopressor-dependent shock

›Respiratory failure or mechanical ventilation

›Ileus with progressive abdominal distension

›Toxic megacolon with or without peritonitis

›Organ failure (AKI, hepatic, respiratory)

›Failure to improve after 24–48 hours of maximal medical therapy

General ward admission criteria

›Hospital admission indications

›Severe CDI (WBC >15,000/µL or creatinine ≥1.5× baseline)

›Inability to tolerate oral medications

›Significant dehydration requiring IV fluids

›Elderly or frail patients without adequate home support

›Immunocompromised host with any CDI

›First presentation with high recurrence risk factors

Surgical consultation

›Surgical referral triggers

›Fulminant CDI with peritoneal signs

›Toxic megacolon not improving within 48–72 hours

›Colonic perforation (free air on imaging)

›Progressive deterioration despite maximal medical therapy

›WBC >50,000/µL or lactate ≥5 mmol/L with fulminant presentation

›Early consultation preferred — do not wait for clinical failure

Discharge criteria

›Criteria for outpatient management

›Nonsevere CDI with WBC ≤15,000/µL and creatinine <1.5× baseline

08Treatment/t80

Antibiotic discontinuation

›Inciting antibiotic management

›Discontinue causative antibiotic if clinically feasible

›Risk-benefit analysis required if antibiotic still needed for concurrent infection

›Discontinuation may alone resolve mild colonization-level presentation

›Class I recommendation: discontinue if medically possible

Initial nonsevere CDI treatment

›First-line regimen (preferred)

›Fidaxomicin 200 mg PO BID for 10 days

›Preferred over vancomycin due to lower recurrence rate

›Narrow-spectrum gut-restricted macrocyclic antibiotic

›ACEP/IDSA 2021 guideline supported; strong recommendation

›Alternative first-line regimen

›Oral vancomycin 125 mg PO QID for 10 days

›Acceptable when fidaxomicin unavailable or cost-prohibitive

›Gut-restricted; negligible systemic absorption

›Not to be administered IV for CDI

›Agents no longer recommended

›Metronidazole: no longer first-line in adults per IDSA 2021

›Reserved only when vancomycin and fidaxomicin are unavailable

›Inferior clinical cure rates compared to vancomycin

›If used: 500 mg PO TID for 10 days

Severe CDI treatment

›Antibiotic regimen for severe CDI

›Oral vancomycin 125 mg PO QID for 10 days

›Fidaxomicin 200 mg PO BID for 10 days (if available)

›Same antibiotic regimen as nonsevere; early surgical consultation added

›Monitoring in severe CDI

›Daily CBC and creatinine to track severity criteria

›Clinical reassessment every 24–48 hours

›Escalate to fulminant protocol if criteria met

Fulminant CDI treatment

›Combination antibiotic protocol

›Oral vancomycin 500 mg PO QID (four-fold higher dose than nonsevere)

›IV metronidazole 500 mg Q8H added for systemic coverage

›Achieves colonic concentrations when enteral delivery compromised

›Monitor QTc and liver function

›Rectal vancomycin if ileus present

›500 mg in 100 mL normal saline retention enema Q6H

›Maintains colonic drug concentrations when oral transit impaired

›Supportive care targets

›Aggressive IV fluid resuscitation for volume depletion

›Electrolyte replacement (potassium, magnesium)

›Nutritional support: enteral nutrition preferred when tolerated

›Do not use anti-motility agents (loperamide) — risk of toxic megacolon

Surgical management of fulminant CDI

›Indications for surgery

›Perforation (absolute)

›Toxic megacolon not responding to 48–72 hours of medical therapy

›Progressive clinical deterioration with organ failure

›WBC >50,000/µL with hemodynamic instability

›Surgical options

›Total abdominal colectomy with end ileostomy

›Traditional standard of care

›Mortality 31–57% in published series

›Permanent ileostomy in many survivors

›Diverting loop ileostomy with antegrade colonic vancomycin lavage

›Emerging colon-preserving alternative

›Comparable mortality to colectomy in matched analyses

›Significantly higher ostomy reversal rates: 80% vs 25% with colectomy

›Colonic lavage: 8 L warmed polyethylene glycol via loop ileostomy

›Followed by vancomycin 500 mg in 500 mL NS administered via loop Q8H

Recurrent CDI treatment

›First recurrence

›Fidaxomicin 200 mg PO BID for 10 days (preferred)

›Extended-pulsed fidaxomicin: 200 mg BID for 5 days then 200 mg every other day for 20 days

›Vancomycin taper/pulse regimen if fidaxomicin unavailable

›125 mg QID for 10 days, then 125 mg BID for 7 days, then 125 mg daily for 7 days, then 125 mg every 2–3 days for 2–8 weeks

›Second or subsequent recurrence

›Antibiotic course followed by microbiome restoration

›Fecal microbiota transplant (FMT)

›Cochrane 2023: FMT superior to vancomycin for preventing further recurrence

›Route: colonoscopic, enema, or nasojejunal

›Efficacy: 80–92% for prevention of further recurrence

›FDA-approved live biotherapeutic products

›Fecal microbiota live-jslm (Rebyota): single rectal dose after antibiotic course

›Fecal microbiota spores live-brpk (Vowst): oral capsule formulation

›Adjunctive therapy

›Bezlotoxumab 10 mg/kg IV (single dose, monoclonal antibody against toxin B)

›Reduces recurrence in high-risk patients

›Indicated with antibiotic therapy in adults with high recurrence risk

›Note: supply availability may be limited

Anti-motility agent restriction

›Contraindicated agents

›Loperamide and other anti-motility agents contraindicated in moderate-severe CDI

›Risk of toxic megacolon by inhibiting evacuation of toxin

›Acceptable only in mild CDI with physician oversight

09Special Populations/sp55

Pregnancy

›CDI in pregnancy

›Immunologic changes of pregnancy may increase susceptibility

›CDI can cause preterm labor and maternal sepsis

›Testing threshold same as non-pregnant (≥3 unformed stools in 24 hours)

›Treatment considerations in pregnancy

›Oral vancomycin 125 mg PO QID for 10 days: preferred first-line

›Negligible systemic absorption; considered safe in pregnancy

›Fidaxomicin: limited safety data in pregnancy; use if benefit outweighs risk

›Metronidazole: avoid in first trimester (teratogenicity concern)

›May be used in second and third trimester if no alternatives available

›FMT safety in pregnancy: limited data; generally reserved for recurrent CDI

›Obstetric considerations

›Involve obstetrics in management of hospitalized pregnant patients

›Fetal monitoring if systemic illness or sepsis

›Dehydration from diarrhea increases preterm labor risk

Geriatric

›Epidemiology in older adults

›Age ≥65 is major independent risk factor for CDI and complications

›Higher rates of severe and fulminant disease

›Higher in-hospital mortality compared to younger adults

›Recurrence rates are higher in elderly

›Atypical presentation in elderly

›Delirium may be the primary presenting feature

›Less fever response due to blunted inflammatory response

›Functional decline as first manifestation

›Ileus without prominent diarrhea more common in frail elderly

›Treatment modifications in elderly

10Background/b65

Epidemiology

›Disease burden

›CDI is the most common cause of healthcare-associated infectious diarrhea

›Estimated 462,000 CDI cases annually in the United States

›Attributable mortality up to 14% in severe CDI

›Approximately 29,000 deaths per year attributed to CDI in the US

›Incidence patterns

›Nosocomial CDI: infection onset >72 hours after hospital admission or within 4 weeks after discharge

›Community-acquired CDI: onset in community or <72 hours after admission without prior healthcare contact in 12 weeks

›Community-acquired CDI now accounts for up to 40% of cases

›Recurrence epidemiology

›Recurrence rate: ~20% after first episode

›Increases to ~40% after second episode

›Up to 60% after third or subsequent recurrence

›Most recurrences occur within 8 weeks of completing treatment

›High-risk populations

›Age ≥65: incidence and severity markedly increased

›IBD: 3-5 fold increase in CDI risk

›Immunocompromised: solid organ transplant, HIV, chemotherapy

›Long-term care facility residents

Pathophysiology

›Organism characteristics

›Clostridioides difficile (formerly Clostridium difficile): anaerobic gram-positive spore-forming bacillus

›Spores are highly resistant to heat, desiccation, and alcohol

›Spores can survive on environmental surfaces for months

›Fecal-oral transmission via contaminated hands, surfaces, and equipment

›Disease mechanism

›Antibiotic disruption of normal gut microbiome creates ecological niche for C. difficile proliferation

›Colonization with toxin-producing strains leads to symptomatic CDI

›Non-toxin-producing strains can colonize without causing disease

›Toxin biology

›Toxin A (enterotoxin): induces fluid secretion and gut inflammation

›Toxin B (cytotoxin): more potent; direct cytopathic effect on colonocytes

›Binary toxin (CDT): expressed by hypervirulent ribotype 027; associated with increased recurrence and mortality

›NAP1/BI/027 strain: fluoroquinolone-resistant hypervirulent strain

›Severity spectrum

›Pseudomembranous colitis: pathognomonic yellow-white plaques on mucosa; present in only ~45–55% of confirmed CDI

›Toxic megacolon: colonic dilation >6 cm with systemic toxicity — life-threatening

›Colonic perforation: end-stage complication with high mortality

›Microbiome restoration

›Loss of colonization resistance from normal flora enables CDI

›Treatment success relies on antibiotic eradication followed by microbiome recovery

›Recurrence often reflects failure of microbiome restoration rather than antibiotic resistance

Therapeutic Considerations

›Antibiotic selection rationale

›Fidaxomicin preferred: narrow spectrum, minimal disruption of normal flora, lower recurrence

›Oral vancomycin: gut-restricted, effective, higher recurrence than fidaxomicin

›Metronidazole: inferior clinical outcomes, higher failure rate, no longer first-line

›IDSA 2021 update: metronidazole displaced from first-line recommendation based on RCT evidence

›Recurrence prevention strategies

›Fidaxomicin extended-pulsed dosing: maintained suppression allows microbiome recovery

›Vancomycin taper: gradual dose reduction reduces rebound CDI after discontinuation

›Bezlotoxumab: neutralizes toxin B, reducing recurrence by ~40% relative risk in high-risk patients

›FMT: restores colonization resistance via donor microbiome; most effective strategy for multiply recurrent CDI

›Microbiota-based therapeutics

›Rebyota (fecal microbiota live-jslm): FDA-approved 2022; single rectal administration

›Vowst (fecal microbiota spores live-brpk): FDA-approved 2023; oral capsules for 3 consecutive days

›Both indicated for prevention of recurrence in adults after antibiotic completion

›Surgical decision-making

›Early surgical consultation is key — waiting until maximal medical failure worsens outcomes

›Diverting loop ileostomy with colonic lavage emerging as colon-preserving alternative to colectomy

›Mortality benefit of DLI vs colectomy still under evaluation but ostomy reversal rates superior

›Infection prevention

›Antimicrobial stewardship: most effective prevention measure

›Contact precautions and environmental disinfection with sporicidal agents (bleach-based)

›Hand hygiene with soap and water mandatory (spores not killed by alcohol)

›Probiotics not recommended by IDSA for CDI prevention

›PPI deprescribing where appropriate reduces recurrence risk

11Patient Discharge Instructions/pdi37

copy discharge instructions

›Diagnosis and treatment instructions

›You have been diagnosed with a Clostridioides difficile (C. diff) infection — a bacterial infection of the colon caused by recent antibiotic use

›Take your prescribed antibiotic exactly as directed for the full course

›Do not stop your medication early even if you feel better

›Finish all of your medication before resuming any probiotics

›Antibiotic and medication guidance

›If prescribed vancomycin capsules: take by mouth, not intravenously

›If prescribed fidaxomicin: take one tablet twice daily with or without food

›Do not take anti-diarrhea medications like loperamide (Imodium) unless your doctor specifically approves

›Avoid unnecessary antibiotics in the future — discuss with your doctor before taking any antibiotic

›Speak with your doctor about stopping your proton pump inhibitor (e.g., omeprazole) if it may not be needed

›Hygiene and prevention

›Wash your hands thoroughly with soap and water after using the toilet — hand sanitizer does not kill C. diff spores

›Wash your hands with soap and water before eating and preparing food

›Clean bathroom surfaces regularly with a bleach-based cleaner while you are still having symptoms

›Do not share towels, utensils, or personal care items with household contacts

›Household members should wash their hands with soap and water after contact with your environment

›Expected recovery course

›Diarrhea typically improves within 3–5 days of starting treatment

›Complete resolution of symptoms may take up to 2 weeks

›You may continue to test positive for C. diff for weeks after treatment — this is normal, do not re-test unless symptoms return

›Post-infectious bowel symptoms (bloating, irregular stool) may persist for several weeks after recovery

›Diet and hydration

›Drink plenty of fluids to replace losses from diarrhea

›Oral rehydration solutions (e.g., Pedialyte, electrolyte drinks) are helpful

›Eat small, frequent meals as tolerated

›Avoid alcohol during your antibiotic course

12References/r33

Guidelines and key sources

›ACG Clinical Guidelines 2021

›Kelly CR, Fischer M, Allegretti JR, et al. ACG Clinical Guidelines: Prevention, Diagnosis, and Treatment of Clostridioides Difficile Infections. American Journal of Gastroenterology. 2021

›doi: 10.14309/ajg.0000000000001278

›IDSA/SHEA 2021 Focused Update

›Johnson S, Lavergne V, Skinner AM, et al. Clinical Practice Guideline by IDSA and SHEA: 2021 Focused Update Guidelines on Management of Clostridioides Difficile Infection in Adults. Clinical Infectious Diseases. 2021

›doi: 10.1093/cid/ciab549

›ASCRS Clinical Practice Guidelines 2021

›Poylin V, Hawkins AT, Bhama AR, et al. The American Society of Colon and Rectal Surgeons Clinical Practice Guidelines for the Management of Clostridioides Difficile Infection. Diseases of the Colon and Rectum. 2021

›doi: 10.1097/DCR.0000000000002047

›ESCMID Guidelines 2021

›van Prehn J, Reigadas E, Vogelzang EH, et al. ESCMID: 2021 Update on the Treatment Guidance Document for Clostridioides Difficile Infection in Adults. Clinical Microbiology and Infection. 2021

›PMID: 34678515

›WSES Guidelines 2019 (Surgical Patients)

›Sartelli M, Di Bella S, McFarland LV, et al. 2019 Update of the WSES Guidelines for Management of Clostridioides Difficile Infection in Surgical Patients. World Journal of Emergency Surgery. 2019

›PMC: 6394026

Key trials and systematic reviews

›FMT Cochrane Review 2023

›Minkoff NZ, Aslam S, Medina M, et al. Fecal Microbiota Transplantation for the Treatment of Recurrent Clostridioides Difficile. Cochrane Database of Systematic Reviews. 2023

›doi: 10.1002/14651858.CD013871.pub2

›Recurrence prognostic factors review 2022

›van Rossen TM, Ooijevaar RE, Vandenbroucke-Grauls CMJE, et al. Prognostic Factors for Severe and Recurrent CDI: Systematic Review. Clinical Microbiology and Infection. 2022

›PMID: 34655745

›DLI vs colectomy analysis 2026

›Zangbar B, Mehta R, Kirsch J, et al. Diverting Loop Ileostomy With Antegrade Colonic Lavage Compared With Colectomy in CDI Colitis: Decade-Long Propensity Score-Matched Analysis. Journal of Trauma and Acute Care Surgery. 2026

›PMID: 41705902

›Recurrent CDI JAMA review 2025

›van Prehn J, Kuijper EJ, Dubberke ER. Recurrent Clostridioides difficile Infections. JAMA. 2025

Evidence & Review

Evidence & Review