Rapid detection of Clostridium difficile-associated diarrhoea in a prospective multicentre study, using a new immunoassay and real-time PCR

R.J. van den Berg, E.S. Bruijnesteijn, H.J. Gerritsen,
H.P. Endtz, E.R. van der Vorm, E.J. Kuijper
(Leiden, Rotterdam, Amsterdam, NL)
Objectives: Clostridium difficile-associated diarrhoea (CDAD) is usually diagnosed by the detection of enterotoxin A (TcdA) and/or cytotoxin B (TcdB) in faecal samples, or by culture of a toxinogenic strain. A recently introduced new rapid immunoassay (Immunocard toxins A and B, Meridian) and an in-house developed real-time PCR were compared in a prospective multicenter study with conventional diagnostics.
Methods: In a prospective study of 4 months, 3 university hospitals participated and tested all faecal samples from patients with diarrhea admitted to the hospital for 3 days or longer for CDAD, irrespective of the physicians request. A conventional enzyme-linked fluorescent assay (ELFA, Vidas CDA2) was used for detection of TcdA and the cytotoxicity assay on Vero-cells was applied as the gold standard. Additionally, the immunocard toxins A and B (ICTAB) and a real-time PCR for the detection of tcdB were included in the study (FICDS, abstr. p. 22, 2004). The sensitivity of the real-time PCR was 1 colony forming unit (CFU) in 0,9% saline and 2800 CFU/g faeces.
Results: Of 471 faecal samples from patients with diarrhoea, 102 (21.7%) were excluded due to a lack of sufficient material for all assays. Of 369 samples included, 75 (20.3%) showed a positive test result in one or more assays. The cytotoxicity test was positive for CDAD in 23 (6.2%) of 369 patients. Of 23 patients with a positive cytoxicity assay, the diagnosis CDAD was not considered in 10 (43%) by the physician. Using the cytotoxicity assay as the gold standard, sensitivity of ELFA, ICTAB and real-time PCR were 69.6%, 91.3% and 87.0%, respectively. The specificity of ELFA, ICTAB and real-time PCR were 95.4%, 96.2% and 95.4%, respectively. The positive predictive value and negative predictive value for ELFA, ICTAB, real-time PCR were 50% and 97.9%, 61.8% and 99.4%, and 55.6% and 99.1%, respectively. Culture of 2 discordant samples only positive by real-time PCR showed the presence of toxinogenic CD in both samples. Culture of 5 samples only positive in ICTAB revealed no toxinogenic CD.
Conclusion: The newly introduced rapid immunoassay is a very rapid and easy-to-perform test for the diagnosis of CDAD. It may be useful for guiding appropriate treatment. The real-time PCR is an excellent instrument to control nosocomial spread of toxinogenic C. difficile.

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