- Currently diagnosed with first CDI after transplant, defined by (1) presence of diarrhea (at least 3 loose stools within a 24-hour period), AND (2) detection of C. difficile cytotoxin in stools by cytotoxin assay, or toxigenic culture, or polymerase chain reaction (PCR) testing for toxin, or enzyme immunoassay, or endoscopic presence of pseudomembranes with the detection of C. difficile in tissue biopsies