Researchers developed and validated a clinical prediction rule for recurrent Clostridium difficile infection (CDI) that is simple, reliable, and accurate and can be used to identify high-risk patients most likely to benefit from measures to prevent recurrence. The clinical prediction rule including other investigators findings, identifies three risk factors for recurrent CDI: age older than 65 years, severe or fulminant illness (by the Horn index), and additional antibiotic use after CDI therapy. The researchers noted that the clinical prediction rule performed consistently and well in both the derivation cohort (63 CDI patients) and validation (89 CDI patients) cohort, correctly identifying 77.3% and 71.9% of patients who had a recurrence, respectively. Dr. Ciaran P. Kelly of Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, and colleagues reported that in the validation cohort, a patient with all three predictive factors had an 87.5% probability of developing recurrence. In high-risk patients with two or more factors, recurrence occurred in 7 of 19 patients (36.5%) compared with 6 of 45 patients (13.3%) of "low-risk" patients with fewer than two predictive factors. A second clinical prediction rule combining data on serum concentrations of IgG against toxin A with the three clinical predictors performed well in the derivation cohort (diagnostic accuracy 93.8%) but not in the validation cohort (diagnostic accuracy 69.2%). Dr. Christina M. Surawicz of the University of Washington School of Medicine wrote in an editorial published with the study that these simple clinical measures alone could identify many with a high risk of recurrence.