G A A b st ra ct s PI-IBS has been reported to be 4.3% after the first episode of CDI. However, there are no reported studies on the incidence or clinical outcomes of PI-IBS in patients after successful treatment of recurrent CDI with fecal microbiota transplantation. The aim of this study was to analyze the incidence and clinical features of PI-IBS in patients undergoing fecal microbiota transplant (FMT) for RCDI, and to describe the microbiota changes associated with PI-IBS in this patient population. Materials and methods: This was an IRB-approved prospective study, which included 27 patients undergoing FMT for RCDI at Sinai Hospital of Baltimore between December 2010 and January 2013. All patients who met the ROME III criteria for IBS after undergoing FMT were included and the rest of the patients were treated as controls. Stool samples were collected from the patients and their donors before and after FMT for microbiota analysis using 16S rRNA pyrosequencing. The end points of the study were to determine the incidence and clinical features of PI-IBS, and to analyze the microbiota changes in the patients with PI-IBS as compared to patients without IBS after FMT, as well as their corresponding donors. Results: A total of 27 patients underwent FMT for RCDI during the study period. Five out of 27 patients (18.5%) developed PI-IBS symptoms within 0.5-6 weeks of FMT (Table 1). These patients met the ROME III criteria for IBS diagnosis and continued to have symptoms for the entire time of follow up (16-35 months). There was no statistical difference in the age, gender, race or duration of symptoms of CDI before FMT between patients who developed PI-IBS after FMT and the patients who did not develop PI-IBS. The 16S rRNA microbiota analysis did not show significant differences in the fecal microbiota diversity (Shannon Index) or abundance of major microbiota members between patients with and without PI-IBS after FMT. However, several minor microbiota members (<0.04%) were less abundant in PI-IBS patients compared to patients without PI-IBS and these changes were consistent with differences in the microbiota compositions of their corresponding donors (Figure 1). Conclusion: PI-IBS incidence was found to be high in patients undergoing FMT for RCDI. Moreover, PI-IBS was associated with specific minor changes in the fecal microbiota composition, which could result from similar differences seen in the donor samples used for FMT in these patients. Table 1: Clinical features of patients with PI-IBS after FMT for RCDI.