Abstract
Background/Aims Clostridium difficile is the most common cause of healthcare-associated infectious diarrhea in the United States. However, few population-based epidemiologic studies of C. difficile infection (CDI) exist. Our aims were to:
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describe the epidemiology of CDI among HMO members from two geographical regions;
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extrapolate the incidence of CDI from these health plans to the U.S. population; and,
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identify patient characteristics that predict inpatient versus outpatient identification of CDIs.
Methods We conducted a population-based, dynamic, retrospective cohort study among Kaiser Permanente Colorado (KPCO) and Northwest (KPNW) enrollees between June 1, 2005 and September 30, 2008. We identified incident CDIs and categorized infections based on identification in the inpatient or outpatient setting. We calculated incidence rates and extrapolated our estimates to the 2007 U.S. population. KPNW and KPCO regional electronic databases provided data on membership, pharmacy dispensings, demographics, clinical measures, and healthcare utilization. Logistic regression determined how strongly patient characteristics predicted inpatient versus outpatient identification of CDIs.
Results We identified 2,879 incident CDIs; 55% were identified in the outpatient setting. In 2007, our total population incidence rate was 13.5 CDI cases per 10,000 person-years; incidence increased with age. Extrapolated to the U.S. white-only population, we estimate that 220,000 cases of CDI occurred among persons 20 years or older in 2007. Baseline characteristics and healthcare utilization prior to identification of CDI in both settings were similar, although individuals with CDI identified in the inpatient setting were older and had greater comorbidity than individuals with outpatient-identified CDI. We identified few strong and independent predictors of setting, although risk for CDI identification in the inpatient setting was associated with an estimated glomerular filtration rate <15 (OR: 4.96; 95% CI: 2.73, 9.02), inflammatory bowel disease (OR: 2.41; 95% CI: 1.45, 4.02), an outpatient antimicrobial dispensing in the previous 180 days (OR: 2.67; 95% CI: 2.13, 3.35), and malignancy (OR: 2.08; 95% CI: 1.60, 2.72).
Conclusion The incidence of CDI among this population is substantial (13.5/10,000 person-years). Because the incidence of and risk for CDIs increases with age, the U.S. burden of CDIs will continue to rise as the proportion of older individuals in the U.S. population rises.
