CSI: a severity index for Clostridium difficile infection at the time of admission

Clostridium difficile is a common cause of nosocomial diarrhoea in the USA. To develop a score model that would help to identify severe versus mild or moderate C. difficile infection (CDI) upon admission we performed a retrospective cohort study. Between January 2004 and December 2007, 255 patients met inclusion criteria for this study. Severe CDI was defined as cases that required colectomy, intensive care unit management, ended in death, or hospitalisation of >10 days. Data recorded included past medical history, physical examination on admission, laboratory data and imaging/colonoscopy data. To create the CDI severity index (CSI) score, we included four risk factors for severe CDI that were identified by univariate analysis: history of malignancy, white blood cell count at admission >20,000/dL, blood albumin <3.0mg/dL, and creatinine at admission >1.5-fold the baseline value. One point was assigned to each of the risk factors. As indicated by a c-statistic of 0.78, the CSI score predicted severe CDI much better than chance (c-statistics of 0.50). The risk of developing severe CDI increased by a factor of 2.9 (95% CI: 1.82-4.59) for each 1-point increase in the CSI score. A CSI score with a cut-off value of 2 had a sensitivity and specificity of 82% and 65%, respectively. The CSI score may quantify the risk of severe CDI at the time of admission, and help in early identification of patients who may benefit from more aggressive treatment.