Clostridioides (Clostridium) difficile colitis (Option D)
This patient has C. difficile infection (CDI), which is the most likely diagnosis given her recent antibiotic exposure for urinary tract infection, new-onset non-bloody diarrhea (6 episodes daily), lower abdominal cramping, leukocytosis, and elevated inflammatory markers. 1
Clinical Reasoning
Why C. difficile is the Most Likely Diagnosis
Recent antibiotic exposure is the single strongest risk factor for CDI, with one-third of colonized patients developing symptomatic infection within 2 weeks of antibiotic therapy 2. This patient's recent UTI treatment with antibiotics places her in the highest-risk category for CDI 1.
The clinical presentation is classic for CDI:
- Three or more unformed stools in 24 hours (she has 6 episodes daily) meets the diagnostic threshold recommended by the Infectious Diseases Society of America 2, 1
- Lower abdominal cramping is characteristic of CDI 2
- Leukocytosis (13,000/μL) supports infectious colitis, particularly CDI 2
- Elevated C-reactive protein (4.0 mg/dL) indicates significant inflammation consistent with CDI 2
- Non-bloody diarrhea is typical for CDI, as pseudomembranes cause inflammation without necessarily causing gross bleeding 2
Why Other Diagnoses Are Less Likely
Ischemic colitis (Option A) typically presents with bloody diarrhea and occurs in patients with vascular risk factors or hypotension. While this patient has atrial fibrillation and takes apixaban, the absence of bloody stools and the recent antibiotic exposure make CDI far more likely 3.
Inflammatory bowel disease (Option B) would be unusual as a new diagnosis in a 60-year-old woman without prior GI symptoms. The temporal relationship to recent antibiotics strongly favors CDI over new-onset IBD 2, 4.
Microscopic colitis (Option C) causes chronic watery diarrhea but would not explain the acute presentation, leukocytosis, elevated CRP, or temporal relationship to antibiotics 2.
Additional Risk Factors Present
This patient has multiple additional CDI risk factors beyond antibiotic use:
- Age 60 years - older adults have higher CDI rates 2
- Methotrexate therapy creates immunosuppression, increasing CDI risk 2
- Potential proton pump inhibitor use (not mentioned but common in this age group) would further increase risk 2
Immediate Management Recommendations
Testing should be performed immediately using a two-step algorithm: GDH screening followed by toxin testing, or NAAT followed by toxin confirmation 1. Single toxin EIA alone is insufficient due to poor sensitivity 1.
If CDI is confirmed, discontinue the causative antibiotic immediately if clinically feasible, as continued antibiotic use significantly increases recurrence risk 1.
Empirical treatment should be initiated while awaiting test results given the high clinical suspicion. Oral vancomycin 125 mg four times daily for 10 days is first-line therapy with approximately 81% clinical success rate 2, 1, 5. Metronidazole 500 mg three times daily for 10 days is an acceptable alternative for non-severe disease 2.
Critical Safety Considerations
Antiperistaltic agents like loperamide are absolutely contraindicated in CDI, as they worsen disease severity, mask symptoms, and can precipitate toxic megacolon by trapping toxins against the colonic wall 1.
Handwashing with soap and water is mandatory for all healthcare contacts, as alcohol-based sanitizers do not inactivate C. difficile spores 1. Mechanical removal through friction and running water is the only effective method 1.
Monitor closely for clinical deterioration including worsening leukocytosis (particularly >15,000/μL), rising creatinine, severe abdominal pain, or ileus, which would indicate severe or fulminant CDI requiring escalated therapy 2.