New molecular methods for the diagnosis of Clostridium difficile infections.

Clostridium difficile is recognized as the major agent responsible for nosocomial diarrhea in hospitalized patients. Accurate diagnosis of C. difficile infection (CDI) is essential for optimal treatment and prevention but continues to be challenging. There are currently two reference assays for the diagnosis of CDI with different targets: the cytotoxicity assay that detects free toxins and the toxigenic culture which detects the organism with the potential to produce toxin. In 2009, nucleic acid amplification tests (NAATs) based on the detection of toxin genes became commercially available for the diagnosis of CDI. These methods have been compared to toxigenic culture (equivalent endpoint) and showed a good correlation. Results can be provided to clinicians within the same day as the stool sample. According to the different assays, the tests are amenable to both batch and on-demand testing. The cost of these assays is still prohibitive for many laboratories and their place among the different diagnostic options remains to be clarified. In particular, these tests again raise the crucial question of the clinical significance of the presence of a toxigenic strain without any free toxin in stools.