[Laboratory diagnosis of Clostridium difficile infection]

For the diagnosis of Clostridium difficile infection (CDI), it is necessary to obtain microbiological evidence of toxigenic C. difficile with a compatible clinical picture (diarrhoea or ileus). Two gold standards exist: cell culture cytotoxicity neutralization assay (specific, but less sensitive than previously acknowledged) and toxigenic culture (very sensitive but less specific because it also detects asymptomatic colonization). These gold standards are not used routinely because at least 2 or 3 days are needed to get a definitive result. Enzyme immunoassays (EIA) are used by most of the French laboratories for the detection of toxins A and B: they provide a quick answer but their sensitivity is insufficient (only 50%). Molecular assays (targeting tcdA or tcdB genes) and glutamate dehydrogenase (GDH) EIA represent an attractive alternative because their high sensitivity (>85%) allow to definitely rule out CDI in the case of a negative result. The presence of GDH is not specific of toxigenic C. difficile: positive results must be confirmed by another method. In the event of a positive molecular assay without toxin presence assessed by EIA or cytotoxicity assay, other causes of diarrhoea should be ruled out before a definitive diagnosis of CDI can be made.