What is a C diff (Clostridioides difficile) carrier screen?

C. difficile Carrier Screening: Purpose and Implications

A C. difficile carrier screen is a diagnostic test that detects the presence of toxigenic Clostridioides difficile in asymptomatic individuals, primarily used to identify potential reservoirs of infection in healthcare settings to reduce transmission and prevent outbreaks. 1

Understanding C. difficile Carriage

• Asymptomatic C. difficile carriage occurs in approximately 10-20% of hospitalized patients 2
• Carriers harbor the organism without symptoms but can shed spores, contributing to environmental contamination and transmission
• Risk factors for carriage include:
  • Recent hospitalization
  • Previous antibiotic exposure
  • Advanced age
  • Lower functional capacity
  • Immunosuppression 2

Diagnostic Methods for Carrier Screening

Carrier screening typically uses the same testing methods as those for symptomatic infection:

1. Nucleic Acid Amplification Tests (NAATs):

   • High sensitivity (80-100%) and specificity (87-99%)
   • Detects toxin genes but cannot distinguish between active infection and colonization 1, 3
   • Often used for perirectal swabs in carrier screening

2. Glutamate Dehydrogenase (GDH) Testing:

   • Sensitive screening test but cannot differentiate between toxigenic and non-toxigenic strains
   • Often used as the first step in a two-step algorithm 1, 3

3. Toxin A/B Enzyme Immunoassays (EIA):

   • Detects actual toxins (not just the organism)
   • Variable sensitivity (32-98%) but high specificity (84-100%) 1

4. Perirectal Swabs:

   • Used specifically for carrier screening
   • High sensitivity (95.7%), specificity (100%), positive predictive value (100%), and negative predictive value (99.1%) compared to stool testing 1

Clinical Significance of Carrier Status

• Risk of Progression: Carriers of toxigenic strains have a significantly higher risk of developing symptomatic CDI

  • Studies show 38.1% of carriers may progress to symptomatic infection compared to only 2% of non-carriers (HR 23.9) 4

• Transmission Risk: Asymptomatic carriers contribute to hospital transmission

  • Up to 29% of CDI cases may be linked to asymptomatic carriers 1
  • Environmental contamination occurs in 34% of rooms occupied by asymptomatic carriers 1

Infection Control Implications

• Contact Precautions: Guidelines recommend placing identified C. difficile carriers in contact (enteric) precautions 1

  • Private room with en-suite facilities when possible
  • Cohort with other CDI patients if private rooms unavailable

• Environmental Measures:

  • Thorough cleaning with sporicidal agents
  • Hand hygiene with soap and water (preferred over alcohol-based sanitizers during outbreaks) 3

Current Recommendations for Carrier Screening

While carrier screening is not universally implemented, it may be considered in specific situations:

• During CDI outbreaks in healthcare facilities
• In high-risk units (e.g., transplant, oncology, geriatric wards)
• As part of comprehensive infection control programs in facilities with high CDI rates 2

Limitations and Considerations

• Positive Predictive Value: In low-prevalence populations, PPV of testing can be as low as 0.28-0.77 1
• Resource Implications: Universal screening may not be cost-effective in all settings
• Lack of Standardization: No consensus exists on optimal screening protocols or frequency
• Management Uncertainty: Limited evidence on how to manage identified carriers beyond isolation 2

Conclusion

Carrier screening represents a potential strategy to reduce CDI rates by identifying asymptomatic reservoirs of C. difficile. While observational studies suggest benefit, more research is needed to determine optimal implementation strategies and to quantify the impact on overall CDI rates in healthcare settings.