Estimating risk of C. difficile transmission from PCR positive but cytotoxin negative cases

Area of Science:

• Clinical Microbiology
• Infectious Diseases
• Molecular Diagnostics

Background:

• Molecular methods like PCR improve Clostridium difficile infection (CDI) diagnosis.
• PCR can detect colonization, posing challenges for treatment and isolation decisions.
• Distinguishing CDI from colonization is crucial for effective patient management.

Purpose of the Study:

• To evaluate the utility of concurrent cytotoxin assay (CYT) and multi-locus variable number tandem repeat analysis (MLVA) in diagnosing CDI.
• To assess the relationship between PCR cycle threshold (Ct) values, bacterial burden, and transmission risk.
• To differentiate between infectious CDI cases and asymptomatic colonization.

Main Methods:

• Real-time PCR was used for initial CDI detection.
• Concurrent cytotoxin assay (CYT) and MLVA were performed on positive PCR samples.
• PCR cycle threshold (Ct) values served as a surrogate marker for bacterial burden.

Main Results:

• MLVA revealed significant genetic diversity among CDI strains, with no widespread outbreaks detected.
• Clostridium difficile infection (CDI) cases negative for cytotoxin assay (CYT-/PCR+) had higher median Ct values (28.2) than CYT+/PCR+ cases (22.5).
• Genetically related strains showed a higher prevalence of cytotoxin positivity.

Conclusions:

• Cases detected by PCR but negative for cytotoxin assay (CYT-/PCR+) contribute to hospital-based transmission.
• The risk of transmission from CYT+/PCR+ cases may be higher than from CYT-/PCR+ cases.
• Integrating molecular and functional assays aids in understanding CDI transmission dynamics.