Trends and changes in Clostridium difficile diagnostic policies and their impact on the proportion of positive samples: a national survey

In June 2012, Israeli guidelines for laboratories were published defining the recommended methods for diagnosis of Clostridium difficile infection (CDI). We conducted this survey to examine the effects of the new recommendations on the proportions of rejected and positive samples by the different methods. A survey was mailed to the directors of all general hospital (GH) and health maintenance organization (HMO) clinical microbiology laboratories. The report was divided into two periods, before and after implementation of the guidelines. Surveys were completed by 13/28 GH laboratories and 5/6 HMO laboratories. All 18 of these laboratories used C.difficile toxin (CDT) enzyme immunoassay alone during the first period of the survey. In the second period, nine laboratories (Group A) used CDT-PCR: two of them used this method exclusively while the other seven used it to resolve most (>90%) of the discrepant results (glutamate dehydrogenase antigen (GDH) +/CDT-]. The other nine laboratories (Group B) used combined GDH/CDT assay, using CDT PCR in only a minority (<20%) of GDH+/CDT- cases. The overall proportion of rejected samples increased from 9.5% in the first period to 13.9% in the second (p<0.001). Between the first and second periods the proportion of positive samples increased from 9.0% to 11.6% in group A laboratories (p<0.001), but decreased from 12.9% to 9.7% in group B laboratories (p<0.001). Implementation of the guidelines has resulted in a significant increase in the proportion of rejected samples and in the proportion testing positive, suggesting more appropriate test utilization and improved sensitivity in the laboratory diagnosis of CDI.