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Abstract
Background
Clostridium difficile is one of the most important pathogens responsible for nosocomial diarrhea. The disease is mediated by two toxins, designated as A and B; therefore, identification of the toxins is important for diagnosis. However, culture or cytotoxin assay are not easily done because of tedious procedures. Instead, toxin A immunoassay is widely used. We evaluated two different enzyme immunoassays (EIA) for C. difficile toxin A and compared them with culture and PCR results.
Methods
A total of 65 stool specimens were examined for toxin A using enzyme linked fluorescent immunoassay (ELFA, VIDAS CD II, Bio-Merieux, France) and enzyme linked immunosolvent assay (ELISA, C. DIFFICILE TOX A II, TECHLAB, USA) and were also cultured for C. difficile using cycloserine cefoxitine fructose agar. We amplified toxin A and B genes using primers NK9-NK 11 and NK104-NK105, respectively, in 23 C. difficile isolates.
Results
The concordance rate between ELFA and ELISA was 76.9%. The sensitivity and specificity of the ELFA and ELISA based on the culture and PCR results for toxin A gene were 84.6%/98.1% and 84.6%/67.3%. Positive and negative predictive values were 91%/96.2% in VIDAS and 78.0%/94.6% in TECHLAB. The positive rates of toxin B genes were 100%, 83.3% and 50% in toxin A positive, variant and negative strains, respectively.
Conclusions
The sensitivities of the ELFA and ELISA for toxin A were the same, but specificity and positive predictive value of the ELFA were higher than those of the ELISA. PCR or EIA method detecting both toxin A and toxin B is strongly recommended, because the variant strains (toxin A negative and toxin B positive) of C. difficile may be more prevalent than were anticipated in Korea.
References
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Table 1.
Comparison of two enzyme immunoassays for toxin A
Table 2.
Comparison of ELFA and ELISA tests with C. difficile culture and toxin A and toxin B PCR results
|
PCR results |
VIDAS |
TECHLAB |
Total | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Toxin A | Toxin B (+) | (+) | Equivocal | (−) | (+) | Equivocal | (−) | ||
| Culture (+) | (+) | 13 (100%) | 7 (10.8%) | 4 (6.2%) | 2 (3.1%) | 11 (16.9%) | 0 | 2 (3.1%) | 13 (20%) |
| Variant* | 5 (83.3%) | 1 (1.5%) | 0 | 5 (7.6%) | 1 (1.5%) | 0 | 5 (7.6%) | 6 (9.2%) | |
| (−) | 2 (50%) | 0 | 0 | 4 (6.2%) | 1 (1.5%) | 1 (1.5%) | 2 (3.1%) | 4 (6.2%) | |
| Culture (−) | ND | ND | 0 | 0 | 42 (64.6%) | 6 (9.3%) | 8 (12.4%) | 28 (43.1%) | 42 (64.6%) |
| Total | 20 (87.0%) | 8 (12.3%) | 4 (6.2%) | 53 (81.5%) | 19 (29.2%) | 9 (13.9%) | 37 (56.9%) | 65 (100%) | |
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