Role of fecal Clostridium difficile load in discrepancies between toxin tests and PCR: is quantitation the next step in C. difficile testing?

• Published in: European journal of clinical microbiology & infectious diseases Vol. 31; no. 12; pp. 3295 - 3299
• Main Authors: Leslie, J. L., Cohen, S. H., Solnick, J. V., Polage, C. R.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.12.2012; Springer; Springer Nature B.V
• Subjects: Adult; Bacterial diseases; Bacterial diseases of the digestive system and abdomen; Bacterial Load; Bacterial Toxins - analysis; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Cell culture; Cell Culture Techniques; Clinical Laboratory Techniques - methods; Clostridium difficile; Clostridium difficile - genetics; Clostridium difficile - isolation & purification; Clostridium Infections - diagnosis; Deoxyribonucleic acid; DNA; Feces; Feces - chemistry; Feces - microbiology; Gastroenterology. Liver. Pancreas. Abdomen; Human bacterial diseases; Humans; Immunoassay; Infectious diseases; Internal Medicine; Laboratories; Medical Microbiology; Medical sciences; Medicine; Other diseases. Semiology; Real-Time Polymerase Chain Reaction; Sensitivity and Specificity; Stomach. Duodenum. Small intestine. Colon. Rectum. Anus; Toxins; United States > US; Toxin Test; Detectable Toxin; Toxigenic Culture; Stool Sample; Fecal Load; Infection; Polymerase chain reaction; Toxin; Microbiology; Clostridiaceae; Clostridium difficile; Clostridiales; Diarrhea; Bacteria; Digestive diseases; Intestinal disease; Molecular biology
• ISSN: 0934-9723; 1435-4373
• DOI: 10.1007/s10096-012-1695-6

Direct tests for Clostridium difficile are 30–50 % more sensitive than tests for C. difficile toxins but the reasons for this discrepancy are incompletely understood. In addition to toxin degradation and strain differences, we hypothesized that C. difficile concentration could be important in determining whether toxins are detected in fecal samples. We performed standard curves on an FDA-approved real-time PCR test for the C. difficile tcd B gene (Xpert C. difficile/Epi, Cepheid) during a prospective comparison of a toxin immunoassay (Meridian Premier), PCR and toxigenic culture. Immunoassay-negative, PCR-positive samples were retested with a cell cytotoxin assay (TechLab). Among 107 PCR-positive samples, 46 (43.0 %) had toxins detected by immunoassay and an additional 18 (16.8 %) had toxin detected by the cytotoxin assay yielding 64 (59.8 %) toxin-positive and 43 (40.2 %) toxin-negative samples. Overall, toxin-negative samples with C. difficile had 10 1 –10 4 fewer DNA copies than toxin-positive samples and most discrepancies between toxin tests and PCR were associated with a significant difference in C. difficile quantity. Of the toxin-positive samples, 95 % had ≥4.1 log 10 C. difficile tcd B DNA copies/mL; 52 % of immunoassay-negative samples and 70 % of immunoassay and cytotoxin negative samples had <4.1 log 10 C. difficile tcd B DNA copies/mL. These findings suggest that fecal C. difficile concentration is a major determinant of toxin detection and C. difficile quantitation may add to the diagnostic value of existing test methods. Future studies are needed to validate the utility of quantitation and determine the significance of low concentrations of C. difficile in the absence of detectable toxin.