ICD-9 diagnostic codes for additional comorbid diagnoses in patients who received a diagnosis of CDI were ranked in order of frequency. The most common 80% of codes were examined, and they corresponded to any code for comorbidity that was found at a frequency of 25 times or more. It was felt that diagnoses that occurred less frequently were unlikely to be risk factors for disease. A total of 205 codes were then categorized into clinically similar groups, and a logistic regression model was generated to establish the risk associated with other comorbid conditions. These categories were bacterial infections, fungal infections, cystic fibrosis, neoplastic disease, hematologic disorders, solid organ transplant, hematopoietic stem cell transplantation, malnutrition, IBD, appendicitis, renal disease, liver disease, human immunodeficiency virus, cardiac disease, pancreatitis, gastrostomy tube status, lupus erythematosus, gastroesophageal reflux, and asthma.