In a 77‑year‑old bedridden female nursing‑home resident with acute diarrhea and abdominal pain and a KUB (kidney‑ureter‑bladder) radiograph showing only a modest amount of stool, what is the most likely diagnosis and initial management?

Most Likely Diagnosis and Initial Management

The most likely diagnosis is Clostridioides difficile infection (CDI), which is the most common identifiable cause of infectious diarrhea in nursing home residents and requires immediate testing and empiric treatment given the high mortality risk in this population. 1

Why C. difficile is the Primary Concern

• C. difficile is the most frequently identified cause of infectious diarrhea in long-term care facilities, accounting for the majority of cases where a pathogen is identified 1, 2
• 10-30% of nursing home residents are asymptomatically colonized with C. difficile, making them highly susceptible to symptomatic infection 1, 2
• Mortality is significantly elevated in elderly patients, with overall mortality estimated at 17% but even higher in older adults, and recent strains are associated with increased severity, hospitalization, intensive care needs, surgical intervention, and death 1, 3
• The KUB showing only "modest stool" argues against fecal impaction and suggests the diarrhea is not overflow from obstruction 4

Immediate Diagnostic Testing

Submit a single diarrheal stool specimen immediately for C. difficile toxin assay (EIA for toxins A or B) 1, 4, 2

• Testing is indicated because she has ≥3 unformed stools with abdominal pain, which meets diagnostic criteria 1, 4, 2
• If the first test is negative but diarrhea persists, submit 1-2 additional stool specimens, as toxin assays are only 60-90% sensitive on a single specimen 1, 5
• Strongly consider C. difficile even without documented recent antibiotic use if severe leukocytosis (≥30,000 cells/mm³) is present, as this can indicate severe disease 1, 4
• Inquire specifically about antibiotic or chemotherapy exposure in the previous 4-6 weeks, as one-third of colonized residents will develop symptomatic infection within 2 weeks of antibiotic exposure 1, 2

Initial Management While Awaiting Test Results

Do NOT administer loperamide, diphenoxylate (Lomotil), or any antimotility agents, as these can precipitate toxic megacolon, mask worsening disease, and significantly increase mortality if C. difficile is present 4, 2, 5

Initiate strict infection control measures immediately:

• Implement contact isolation to prevent nosocomial transmission to other residents 1, 2
• Enforce strict handwashing with soap, friction, and running water after all patient contact, as alcohol-based hand sanitizers do not inactivate C. difficile spores 1, 4, 2, 5
• Educate all staff that mechanical removal of spores through handwashing is essential 1

Provide aggressive fluid replacement:

• Administer oral rehydration solution (ORS) for mild to moderate dehydration 4, 5
• Administer intravenous isotonic fluids (lactated Ringer's or normal saline) if she shows signs of severe dehydration or cannot tolerate oral intake 4, 5
• Fluid replacement is the cornerstone of treatment and should not be neglected 4

When to Start Empiric Antibiotic Therapy

If clinical suspicion is high and the patient appears moderate-to-severely ill (significant abdominal pain, leukocytosis, fever, or clinical deterioration), start oral vancomycin 125 mg four times daily while awaiting test results 2

• This recommendation is based on the high mortality risk in elderly bedridden patients and the severity of recent C. difficile strains 1, 2
• Stop any causative antibiotics immediately if clinically feasible, as continued use significantly increases recurrence risk 2

Additional Differential Considerations

If C. difficile testing is negative after multiple specimens:

• Submit stool for culture to isolate invasive enteropathogens (Campylobacter jejuni, Salmonella, Shigella species, E. coli O157:H7) if symptoms suggest colitis 1
• Consider norovirus, which is highly contagious in nursing homes and carries significant mortality in this population, though it typically presents with more vomiting 1
• Evaluate for Giardia and other protozoa if symptoms persist beyond 7 days without another identified cause 1

Critical Pitfalls to Avoid

• Never assume the modest stool on KUB rules out infectious diarrhea—the radiograph does not exclude C. difficile or other pathogens 4
• Do not delay testing while trying symptomatic management, as progression to severe disease carries significant mortality risk in elderly patients 5
• Avoid unnecessary antibiotics during workup, as this can precipitate symptomatic infection in colonized residents 1, 5
• Do not use antimotility agents while C. difficile remains in the differential, even if testing is pending 4, 2, 5

When to Transfer to Acute Care

Transfer immediately if she develops:

• Signs of ileus or peritonitis (absent bowel sounds, rigid abdomen, rebound tenderness) 1
• Severe leukocytosis ≥30,000 cells/mm³ 1, 4
• Hypotension, altered mental status, or other signs of sepsis 1
• Inability to maintain hydration orally 4

These patients require urgent CT imaging and intensive monitoring for possible toxic megacolon or need for surgical intervention 1