Comparison of a novel chemiluminescent based algorithm to three algorithmic approaches for the laboratory diagnosis of Clostridium difficile infection
© Goret et al. 2015
Received: 9 October 2015
Accepted: 1 December 2015
Published: 23 December 2015
Rapid commercial assays, including nucleic acid amplification tests and immunoassays for Clostridium. difficile toxins, have replaced the use of older assays. They are included in a two-step algorithm diagnosis, including first the detection of the glutamate dehydrogenase (GDH) as a screening method and second the detection of toxins as a confirmatory method. Although assays that detect the presence of free toxins in feces are known to lack sensitivity, they are preferable to confirm infection. We evaluated the accuracy of the chemiluminescence-based method detecting C. difficile GDH and free toxins A/B (DiaSorin algorithm) to an enzyme-immunoassay (EIA) for GDH with a molecular toxins test (Meridian algorithm), EIA-GDH and an EIA-toxins A/B algorithm (Alere algorithm) with and without toxigenic culture for confirmation.
A total of 468 diarrhoeal and loose stool samples were included in the study. A positive result was defined by a positive GDH and a positive toxin test. Discordant samples were resolved using an enriched toxigenic culture considered as the reference method. After resolution, the DiaSorin algorithm showed a high sensitivity (86.7 %) compared to that of the Alere algorithm with (60.0 %) and without (50.0 %) confirmation by culture and was as sensitive as the Meridian algorithm (90.0 %), while the specificities were similar: 99.1, 99.5, 99.5 and 98.9 %, respectively.
The DiaSorin algorithm was as sensitive as an algorithm including nucleic acid amplification test for toxins. Chemiluminescence toxin-enhanced signal assay compensates the lack of sensitivity usually observed for EIA tests for toxins.
KeywordsClostridium difficile Algorithm Chemiluminescence Diagnosis Toxins DiaSorin
Clostridium difficile is a major cause of healthcare-associated diarrhoea. Many different approaches are available for the laboratory diagnosis of C. difficile infection (CDI). American  and European  guidelines recommend testing patients with a two-step algorithm including the detection of glutamate dehydrogenase (GDH) as a screening method followed, in case of positive result, by the detection of free toxins or their genes as a confirmation method. The DiaSorin Liaison® C. difficile GDH and toxins A and B (DiaSorin, Saluggia, Italy) is a sandwich chemiluminescent immunoassay (CLIA) performed on a stool extract. Luminescent assays for C. difficile diagnosis have not been previously reported in the literature. This method may be more reliable than enzyme immunoassays (EIA), which are known to lack sensitivity for free toxin detection. The objective of the study was to evaluate the performances of the newly available chemiluminescence-based DiaSorin algorithm for the detection of GDH and free toxins A and B using the Liaison apparatus in a routine laboratory.
The DiaSorin algorithm was compared to three other algorithms: (1) a widely used EIA algorithm including, the C. Diff Quik Chek GDH® followed by detection of free toxins A and B, TOX A/B Quik Chek® test (Alere, Waltham, MA, USA), (2) the same EIA-based algorithm with toxigenic culture as a third step in case of negative toxin results; for this purpose, the stools were directly inoculated on a cycloserine-cefoxitin-amphotericin agar (bioMérieux, Marcy l’Etoile, France) incubated at 37 °C for 3 days in an anaerobic atmosphere and the isolates were then tested for toxins A and B using the TOX A/B Quik Chek® (Alere), and (3) a very sensitive algorithm [3–8] using the EIA ImmunoCard® C. difficile GDH for screening followed by a loop-mediated isothermal amplification assay for tcdA toxin gene detection (illumigene ® Meridian, Cincinnati, OH, USA). The manufacturer’s recommendations were followed. All algorithms included a preliminary screening step for the detection of GDH and then, if positive, the stool samples were tested for toxins or toxin genes. The specimens that tested positive for the toxins were considered positive. The specimens that tested negative for GDH or for toxins were considered negative. In our study, the aggregate criteria for a true positive or a true negative result were a positive or negative result for the four algorithms, respectively. If an algorithm result was different from the three others, the sample was considered discordant. The discordant samples were resolved using enriched toxigenic culture (ETC) considered as a reference method and performed at the French National Reference Laboratory for C. difficile (Paris, France): stool samples were inoculated in pre-reduced taurocholate-cycloserine-cefoxitin BHI broth incubated for 5 days at 37 °C under anaerobic conditions; the broth was then plated onto laboratory standard selective plates containing taurocholate, cycloserine and cefoxitin. Toxinogenicity of the strains was demonstrated using an in-house polymerase chain reaction (PCR) targeting tcdA and tcdB genes. After ETC, a stool sample was considered positive for toxigenic C. difficile if the toxin genes were detected.
Clostridium difficile diagnostic test performances using enriched toxigenic culture as the reference standard
(%) Sensitivity (95% CI)
(%) Specificity (95% CI)
Positive predictive value (%) (95% CI)
Negative predictive value (%) (95% CI)
DiaSorin algorithm = CLIA GDH + CLIA toxins A/B
Meridian algorithm = EIA GDH + NAAT for toxin gene
2-Step Alere algorithm = EIA GDH + EIA toxins A/B
3-Step Alere algorithm = EIA GDH + EIA toxins A/B + toxigenic culture
Turnaround time and reagent costs to detect Clostridium difficile infection in the laboratory
Labor time (min)
Turnaround time of test (min)
Individual or series test
Algorithm cost ratio relative to DiaSorin algorithm (%)
Liaison random access
Toxins A and B
Liaison random access
C. DIFF Quik Chek GDH®
TOX A/B Quik Chek®
The limitation of the study was the small number of positive cases rendering the estimation of sensitivity with a large confidence interval. Given the low incidence of CDI in this population, a larger number of specimens should have been evaluated. Choosing the right diagnostic approach is a matter of test accuracy, turnaround time, and cost for routine use in a clinical laboratory. In conclusion there is a good performance of the DiaSorin assay in comparison to the three other approaches. This method is sufficient for the diagnosis of CDI and there is no need for a confirmation test because the sensitivity of the test is as high as the molecular method. This algorithm could replace the others.
JG, JB and SL carried out the four different algorithms at the Bacteriology Laboratory of the Bordeaux University Hospital (Bordeaux, France). AP performed the reference method for the discordant samples at the French National Reference Laboratory for C. difficile (Paris, France). JG and JB collected the data and drafted the manuscript. JG, FM, CE and FB conceived of the study and participated in its design and coordination. FM, CB, CE and FB helped to draft the manuscript. All authors read and approved the final manuscript.
We thank the National Reference Laboratory for Clostridium difficile for their help. We are grateful to DiaSorin France and Meridian Bioscience France for providing kits and technical support for this study.
The authors declare that they have no competing interests.
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