Clostridium difficile is an anaerobic Gram-positive, spore-forming, toxin-producing bacillus transmitted among humans through the faecal oral route. Despite increasing carriage rates and the presence of C. dfficile toxin in stool, patients with CF rarely appear to develop typical manifestations of C. dfficile infection (CDT). In this study, we examined the carriage, toxin production, ribotype distribution and antibiotic susceptibility of C. difficile in a cohort of 60 adult patients with CF who were pre-lung transplant. C. dfficile was detected in 50% (30/60) of patients with CF by culturing for the bacteria. C. dicile toxin was detected in 63% (19/30) of C. dffficik-positive stool samples. All toxin-positive stool samples contained toxigenic C. dfficile strains harbouring toxin genes, tcdA and tcdB. Despite the presence of C. dlcile and its toxin in patient stool, no acute gastrointestinal symptoms were reported. Ribotyping of C. difficile strains revealed 16 distinct ribotypes (RT), 11 of which are known to be disease-causing including the hyper-virulent RT078. Additionally, strains RT002, RT014, and RT015, which are common in non-CF nosocomial infection were described. All strains were susceptible to vancomycin, metronidnzole, fusidic acid and rifampicin. No correlation was observed between carriage of C. dijficile or. any characteristics of isolated strains and any recorded clinical parameters or treatment received. We demonstrate a high prevalence of hypervirulent, toxigenic strains of C. dlcile in asymptomatic patients with CF. This highlights the potential role of asymptomatic patients with CF in nosocomial transmission of C. dfficile. (C) 2016 European Cystic Fibrosis Society. Published by Elsevier B.V. All rights reserved.