Impact of changes in Clostridium difficile diagnostic testing on detection of C. difficile infection and all England mandatory surveillance data

Summary Following the report of the Centre for Evidence-based Purchasing, which suggested poor performance of Clostridium difficile testing kits, revised guidance was issued by the Department of Health (England) recommending a two-test algorithm. The aim of this study was to survey English National Health Service (NHS) diagnostic microbiology laboratories using an electronic questionnaire to investigate changes in laboratory procedures in response to the guidance and model the impact these changes had on national and locally reported data. It was found that 24% of laboratories had changed testing procedures and there was no evidence of an overall effect on the English mandatory surveillance data used for performance management. It was shown that there could be an impact on an individual NHS Trust’s case numbers, and a simple model for Trusts to predict these changes in C. difficile laboratory diagnosis was developed. There was also evidence of the use of variable sample selection criteria, which could affect the positive and negative predictive values of local testing.