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We evaluated the performances of 2 PCR assays (BD GeneOhm and Seegene ACE) for direct detection of tcdB from stool specimens. The concordance rate between BD and Seegene was 96.3%. The sensitivities, specificities, positive predictive values (PPVs), and negative predictive values (NPVs) of BD and Seegene were 95.7%, 96.5%, 91.8%, and 98.2% and 90.0%, 97.1%, 92.6%, and 96.0%, respectively.

Enzyme immunoassays for TcdA and/or TcdB are widely used for diagnosis of C. difficile infection. This study compared the performance of the new VIDAS C. difficile Toxin A & B assay (CDAB) with that of the existing VIDAS C. difficile Toxin A II assay (CDA) in a tcdA(-)tcdB(+) prevalent area. A total of 555 fecal samples were cultured and tested using CDAB and CDA. C. difficile was isolated in 150 samples and the concordance rate was 81.8% (454/555) between CDAB and CDA. PCR assays for tcdA and/or tcdB were used as a confirmatory test on C. difficile strains recovered from culture positive cases (n=150) and on fecal specimens in culture negative/CDAB positive or equivocal cases (n=27). The number of tcdA(+)tcdB(+), tcdA(-)tcdB(+), and tcdA(-)tcdB(-) strains on culture positive isolates (n=150) were 75 (50.0%), 41 (27.3%), and 34 (22.7%), respectively. PCR assays for tcdB gene alone in stool specimens (n=27) showed positivity in five cases. The sensitivity of VIDAS CDAB was higher than that of VIDAS CDA (65.3% vs. 29.8%), by more than 2-fold. The specificity of CDAB was almost the same as CDA (93.8% vs. 94.5%). Toxigenic culture of C. difficile isolates in culture positive/VIDAS CDAB negative cases (n=62) additionally detected 22 VIDAS CDAB positive and 9 VIDAS CDAB equivocal cases. The VIDAS CDAB assay detects more tcdA(+)tcdB(+) strains (60% vs. 45.3%) and tcdA(-)tcdB(+) strains (70.7% vs. 0%) compared with VIDAS CDA.

Background: Enzyme immunoassay (EIA) capable of detecting both toxin A and toxin B is strongly recommended for the diagnosis of Clostridium difficile associated disease. Therefore, we evaluated two different EIAs for the detection of C. difficile toxin A/B., Methods: For a total of 228 stool specimens we performed bacteriologic cultures for C. difficile and examined for toxin A and toxin B using enzyme linked fluorescent immunoassay (ELFA; VIDAS CDAB, Bio-Merieux sa, France) and ELISA (C.DIFFICILE TOX A/B II, TECHLAB, USA). We also performed PCR assays for toxin A and B genes in 117 C. difficile isolates that grew from the stool cultures and compared the results with those obtained with the two different EIAs., Results: The concordance rate between ELFA and ELISA was 85.5% (195/228). Using the culture and PCR results as the standard, the sensitivity/specificity of the ELFA and ELISA were 65.0%/72.1% and 71.8%/70.3%, and for positive/negative predictive values were 78.4%/69.6% and 71.8%/70.3%, respectively (P value >0.05). No differences were observed between the results of ELFA and ELISA with toxin A(-) toxin B(+) strains of C. difficile., Conclusions: The sensitivity of the ELISA was slightly higher than that of ELFA for toxin A and toxin B, but the specificity and positive predictive value of the ELFA were rather higher than those of the ELISA, although no statistical differences were observed. A bacteriologic culture and PCR assay for toxin genes are recommended in case the both EIAs are negative.

Sixty percent to 80% of Clostridium difficile isolates in Korea have been reported to be toxigenic. However, over 1 year, we encountered a high number of tcdA-tcB+ strains associated with pseudomembranous colitis (PMC). C. difficile was isolated from 224 of 471 specimens (47.6%) from 371 patients. A subset of the culture-positive specimens (n = 106), containing no duplicate cases, was randomly selected for tcdA and tcdB polymerase chain reaction (PCR) assays. PCR results showed that tcdA+tcdB+ and tcdA-tcdB+ strains accounted for 39.6% (42/106) and 50.9% (54/106), respectively. Endoscopy, performed on 55/106 patients, revealed 29 with PMC, 5 with colitis, 14 with other colon diseases, and 7 normal cases. Among the 29 PMC cases, 21 (72.4%) were associated with tcdA-tcdB+ strains (P = 0.0016). These results revealed the possible emergence of tcdA-tcdB+ C. difficile strains in Korea, and these variant strains could evoke a higher rate of PMC than tcdA+tcdB+ strains.