What is the proper procedure for collecting a stool specimen for Clostridium difficile testing in a patient, considering factors such as age, medical history, including recent antibiotic use, and underlying conditions?

Stool Specimen Collection for Clostridioides difficile Testing

Only collect unformed (liquid or soft) stool specimens from patients with ≥3 unformed stools in 24 hours who have no obvious alternative explanation for diarrhea, and do not collect specimens from patients who have received laxatives within the previous 48 hours. 1

Patient Selection Criteria for Specimen Collection

Who should have specimens collected:

• Patients with unexplained new-onset diarrhea defined as ≥3 unformed stools in 24 hours 1, 2
• Patients with healthcare-associated diarrhea regardless of antibiotic exposure 2
• Community patients with persistent diarrhea after negative testing for common enteropathogens 1, 3
• Patients with recent antibiotic use (within 4-6 weeks), chemotherapy exposure, or hospitalization 2, 3

Who should NOT have specimens collected:

• Patients receiving laxatives within the previous 24-48 hours 1, 3
• Asymptomatic patients (except for epidemiological studies) 1
• Neonates or infants ≤12 months of age with diarrhea, due to high asymptomatic carriage rates 1
• Patients with formed stool, as this leads to false positives and unnecessary treatment 1, 3

Specimen Type and Collection Method

Standard collection approach:

• Collect only unformed (liquid or soft) stool that takes the shape of the container 1
• Laboratories should reject formed stool specimens to improve test specificity 1
• A single diarrheal stool specimen is typically sufficient for initial testing 1

Alternative for patients with ileus:

• For patients with suspected severe CDI complicated by ileus who cannot produce stool specimens, perirectal swabs tested by PCR provide an acceptable alternative with sensitivity of 95.7%, specificity of 100%, and negative predictive value of 99.1% 1
• This approach is specifically recommended for surgical patients or those with signs of severely disturbed bowel function 1

Critical Collection Pitfalls to Avoid

Common errors that compromise diagnostic accuracy:

• Testing patients on laxatives or promotility drugs, which creates false clinical presentations 1
• Collecting formed stool specimens, which detects asymptomatic colonization rather than active infection 1, 3
• Repeat testing within 7 days during the same diarrheal episode, which is not recommended and wastes resources 1
• Testing for "test of cure" in asymptomatic patients after treatment, which is never indicated 1

Institutional Coordination for Appropriate Specimen Submission

Healthcare facilities should establish preagreed criteria:

• Clinicians and laboratory personnel should agree institutionally to submit specimens only from patients meeting clinical criteria (≥3 unformed stools in 24 hours, no laxatives) 1
• Some institutions use electronic medical record forms requiring providers to document frequency and consistency of bowel movements before testing is performed 1
• Empowering healthcare workers collecting specimens to discuss stool consistency with clinicians reduces inappropriate testing 1
• Laboratories can collaborate with infection prevention and antibiotic stewardship teams to periodically audit appropriateness of testing through chart review 1

Age-Specific Considerations

Pediatric patients:

• Never routinely test neonates or infants ≤12 months of age due to high prevalence of asymptomatic carriage (strong recommendation) 1
• For children >12 months, use the same criteria as adults: ≥3 unformed stools in 24 hours with no alternative explanation 1

Community-acquired cases:

• Community-acquired CDI occurs across all age ranges (1-92 years), with 18% of cases under age 20 1, 3
• Do not exclude testing based on absence of traditional risk factors, as 25-26% of community cases lack healthcare exposure or recent antibiotics 1, 3

Transport and Storage Considerations

• While the guidelines focus on clinical criteria for collection, specimens should be transported promptly to avoid toxin degradation 1
• Storage at 4°C for up to 56 days has minimal effect on toxin detection, but multiple freeze-thaw cycles may reduce toxin titers 1