The diagnosis of Clostridium difficile-associated disease

There are well-documented risk factors associated with the development of antibiotic-associated diarrhoea; knowledge of these and of the typical signs and symptoms should alert the clinician to the possibility of Clostridium difficile-associated diarrhoea (CDAD). It is therefore common practice in large general hospitals for clinicians to request, and for laboratories to include, investigations for C. difficile on in-patient stool specimens to confirm a diagnosis of CDAD. The laboratory methods used to investigate for CDAD are divided into two main categories: those that are aimed at detecting the presence of C. difficile or its products, and those that detect either of its two major toxins, A (enterotoxin) and B (cytotoxin). Within each of these broad strategies there are various rationales which are reviewed here.