Multicentre evaluation of a new rapid Tox A+B test (Meridian ICTAB) for the diagnosis of Clostridium difficile-associated diarrhoea

J. Van Broeck, J. Verhaegen, D. Van Kerkhoven, B. Van Meensel, M. Delmee (Brussels, Leuven, B)
Objective: We evaluated the performances of a new rapid enzyme immunoassay (Tox A+B) for the detection of Clostridium difficile Toxins A and B (Immunocard Toxin A&B — ICTAB, Meridian Cincinnati, Ohio USA) on stool specimens received in two university hospitals. Tox A+B was compared to a toxin A latex immunoassay (Tox A) (C. difficile toxin A test, Oxoid Basingstoke England) and to the standard procedure in use in the laboratories which comprises faecal cytotoxin detection and faecal toxigenic culture.
Methods: Stools were from inpatients older than 2 years and suffering from nosocomial diarrhoea following antimicrobial- or chemo-therapy in two large university hospitals (St Luc-UCL hospital in Brussels and Gasthuisberg-KULeuven hospital in Leuven). Tox A+B and Tox A were performed according to the respective manufacturer»s instructions. Faecal tissue culture assay was performed using HeLa cells. Toxigenic culture consisted of culture of faeces on CCFA medium followed, if the culture was positive, by toxin detection on colonies using the Tox A and Tox A+B assays. Toxigenic culture was considered the gold standard.
Results: A total of 533 stools from 398 patients were included. Culture was positive in 62 cases (11.6%) and 50/62 (80.6%) strains were shown to be toxigenic. The following table summarizes the main results. The assays» sensitivity, specificity, PPV and NPV were respectively: Cytotoxin assay : 56%, 100%, 100%, 95.6% Tox A : 66%, 98.6%, 82.5%, 96.5% Tox A+B : 88%, 99.1%, 91.7%, 98.8% Among the 50 stools with a positive toxigenic culture, 24 were positive for the three toxin assays, 9 were positive for Tox A and Tox A+B, 4 for Tox A+B and faecal cytotoxin, 8 for Tox A+B only and 7 for none of the three tests. Among the 4 specimens with positive Tox A+B and negative culture, one was from a patient who had a positive stool culture ten days before.
Conclusion: Tox A+B was the most sensitive and highly specific assay for the detection of C. difficile toxins in faecal specimens. Moreover, compared to other detection methods, Tox A+B is particularly fast, easy to perform and has the added benefit of detecting both toxins.
 Toxigenic              Faecal             Tox A               Tox B
   culture              cytotoxin

                            Pos  Neg         Pos  Neg         Pos  Neg
Pos N=50             28      22          33      17          44       6
Neg N=483            0     483            7    476            4   479

15th European Congress of Clinical Microbiology and Infectious Diseases (ECCMID)
2-5 April 2005 — Copenhagen, Denmark