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Abstract
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.
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Table 1.
Comparison of toxin A and B enzyme immunoassay results
| ELFA (VIDAS) | Total | |||
|---|---|---|---|---|
| (+) | equivocal | (–) | ||
| ELISA (+) | 96 | 5 | 16 | 117 |
| (TECHLAB) (–) | 1 | 11 | 99 | 111 |
| Total | 97 | 16 | 115 | 228 |
Table 2.
Comparison of ELFA (VIDAS) and ELISA (TECHLAB) tests with C. difficile culture and PCR assay detecting both toxin A and B
| Culture positive (N=155) | Culture negative (N=73) | Total | ||
|---|---|---|---|---|
| PCR positive∗ | PCR negative | |||
| ELFA | ||||
| + | 76 (65.0%) | 4 (10.5%) | 17 (23.3%) | 97 (42.6%) |
| Equivocal | 6 (5.1%) | 3 (7.9%) | 7 (9.6%) | 16 (7.0%) |
| - | 35 (29.9%) | 31 (81.6%) | 49 (67.1%) | 115 (50.4%) |
| ELISA | ||||
| + | 84 (71.8%) | 7 (18.4%) | 26 (35.6%) | 11 7 (51.3%) |
| - | 33 (28.2%) | 31 (81.6%) | 47 (64.4%) | 111 (48.7%) |
| Total | 117 (100%) | 38 (100%) | 73 (100%) | 228 (100%) |
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