Table 3.

C. difficile Infection (CDI) Classification based on Disease Severity

Disease Category	Clinical and Laboratory Signs	Associated Risk Factors
Mild to moderate CDI	Diarrhea without systemic signs of infection, WBC< 15,000 cells/mL, and serum creatinine < 1.5 times baseline15	Antibiotic use, previous hospitalization, longer duration of hospitalization, use of proton pump inhibitors, receipt of chemotherapy, chronic kidney disease, and presence of a feeding-tube10–14.
Severe CDI	Systemic signs of infection, and/or WBC ≥ 15,000 cells/mL, or serum creatinine ≥ 1.5 times the premorbid level 15	Advanced age, infection with BI/NAP1/027 strain 115,116.
Severe, complicated CDI	Systemic signs of infection including hypotension, ileus, or megacolon 15	See above, plus recent surgery, history of inflammatory bowel disease and intravenous immunoglobulin treatment43
Recurrent CDI	Recurrence within 8 weeks of successfully completing treatment for CDI 16,20	Patient age ≥65 years, concomitant antibiotic use, presence of significant comorbidities, concomitant use of proton pump inhibitors, and increased initial disease severity 16