OBJECTIVE: To develop and validate a clinical prediction scale for hospital-onset Clostridium difficile infection (CDI).METHODS: A community-based, 360-bed hospital located in the suburbs of a metropolitan area in the United States served as the setting for the present retrospective cohort study. The cohort consisted of patients admitted to the adult medical service over a six-year period from October 2005 to September 2011. The cohort was divided into derivation (October 2005 to September 2009) and validation (October 2009 to September 2011) groups. The primary outcome measure was hospital-onset CDIs identified as stool positive for C difficile after 48 h of hospital admission ordered for new-onset unformed stool by the treating physician.RESULTS: In the derivation phase, 35,588 patients were admitted to the medical service and 21,541 stayed in hospital beyond 48 h. A total of 266 cases of CDI were identified, 121 of which were hospital onset. The developed clinical prediction scale included the onset of unformed stool (5 points), length of hospital stay beyond seven days (4 points), age >65 years (3 points), long-term care facility residence (2 points), high-risk antibiotic use (1 point) and hypoalbuminemia (1 point). The scale had an area under the receiver operating curve (AUC) of 0.93 (95% CI 0.82 to 0.94) in predicting hospital-onset CDI, with a sensitivity of 0.94 (95% CI 0.88 to 0.97) and a specificity of 0.80 (95% CI 0.79 to 0.80) at a cut-off score of 9 on the scale. During the validation phase, 16,477 patients were admitted, of whom 10,793 stayed beyond 48 h and 58 acquired CDI during hospitalization. The predictive performance of the score was maintained in the validation cohort (AUC 0.95 [95% CI 0.93 to 0.96]) and the goodness-to-fit model demonstrated good calibration.CONCLUSION: The authors developed and validated a simple clinical prediction scale for hospital-onset CDI. This score can be used for periodical evaluation of hospitalized patients for early initiation of contact precautions and empirical treatment once it is validated externally in a prospective manner.