This was a single centre retrospective analysis of C difficile sample numbers and numbers of infections over a 6-year period (January 2010 to December 2015) during which the testing method was changed from toxin A and B enzyme immunoassay (EIA) to a C difficile NAAT assay. The study centre is a 750-bed tertiary care university hospital in the south of Milan characterized by high risk populations, of our admissions more than an half are for surgery, with a Bone Marrow Transplant Unit and Cancer Unit, and a total of 25 ICU beds.
During the first 2 years, all samples were tested with a toxin A/B enzyme immunoassay (TOXA/B QUIK CHEK, Techlab, Blaksburg, VA) and in the following four years testing was by a commercial NAAT assay (XpertC difficile, Cepheid, Sunnyvale, CA) as a stand-alone test. All tests were performed strictly in accordance with manufacturer’s instructions.
During the period when the EIA toxin test was used there were no clear guidelines for sampling. Following the introduction of the NAAT clear criteria for testing were implemented and a detailed internal guideline was emailed to all clinicians explaining that only unformed stool samples were to be tested and in the case of a previous positive result the patient would only be re-tested after 30 days and in the case of a previous negative result only after 10 days. Samples not meeting these criteria were rejected and the microbiology laboratory did not examine the sample explaining the reason in the laboratory report. Clinicians could over-rule these decisions in discussion with infection specialists in cases where special circumstances pertained.
Positive cases were reported by telephone to the physician or ward nurse immediately they became available and this was followed up by an email to the Infection Prevention team. Positive patients who were not already in a single room were placed in isolation or, where this was not possible, cohorted in a double room with another C difficile positive patient. Positive patients remained in isolation until resolution of symptoms. Following patient discharge strict environmental cleaning and disinfection of the isolation room was carried out.
Study patients included all those for whom CDI was suspected and one or more samples submitted for a CDI diagnostic test. Each case of CDI was reviewed by an epidemiology nurse and evaluated as to whether healthcare or community acquired. The definition of healthcare acquired used in this study was the appearance of symptoms more than 48 h following admission to hospital.