The impact of Clostridium difficile fecal loads on diagnostic test results is poorly understood, but it may have clinical importance. In this study, we investigated the relationship between C. difficile fecal load and the results of four assays: a glutamate dehydrogenase (GDH) enzyme immunoassay (EIA), a toxin A/B antigen EIA (ToxAB), a cell culture cytotoxicity assay (CCA), and PCR targeting the tcdB gene. We also compared the PCR cycle threshold (C T ) with the results of quantitative culture using Spearman's rank correlation coefficient. .35 to 7.83), respectively. Group 1 samples had lower fecal loads than those from each of the other groups (P < 0.001). Group 2 samples had lower fecal loads than those from groups 3 and 4 (P < 0.001). There was a significant correlation between PCR C T and fecal loads ( ‫؍‬ ؊0.697; P < 0.001). NAP1 strains were associated with the detection of toxins by EIA or CCA (P ‫؍‬ 0.041). This study demonstrates an association between C. difficile fecal load and the results of routinely used diagnostic tests.

Clinical features of Clostridium difficile infections (CDI) detected by PCR, but not by conventional methods, are poorly understood. We compared the clinical features of CDI cases detected by PCR only and cases detected by both PCR and a three-step algorithm. We performed a retrospective cohort study of patients fulfilling a standardized definition over a 13-month period. Stool specimens were tested in parallel by PCR and an algorithm based on enzyme immunoassay and cytotoxicity assay (EIA/CCA). Clinical features of CDI cases detected by PCR only and cases detected by PCR and EIA/CCA were compared by univariate logistic regression. In all, 97 patients (31 PCR+ and 66 PCR+EIA/CCA+) met the inclusion criteria. Compared with cases detected by both PCR and EIA/CCA, CDI cases detected by PCR only were younger (65.4 versus 76.3 years; p 0.001), had a lower absolute neutrophil count (mean, 9.4 × 10(9) /L versus 12.5 × 10(9) /L; p 0.04), were less likely to receive oral vancomycin (2/31 versus 25/66; p 0.005) or combination therapy (0/31 versus 16/66; p 0.04), and had fewer complications (6/31 versus 29/66; p 0.02), despite presenting a higher number of bowel movements on the day of diagnosis (median, 6.0 versus 3.0; p 0.02). They had also a lower C. difficile faecal bacterial load (mean, 5.04 versus 6.89 log10 CFU/g; p <0.001). The CDI cases detected by PCR only and cases detected by both PCR and EIA/CCA have different clinical features, but whether these two populations can be managed differently remains to be determined.

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