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Purpose: It is unknown how C. difficile colitis (CDC) patients differ in terms of hospital costs, length of hospital stay (LOS) and readmission rates depending on whether patients were admitted principally to treat CDC versus developing CDC while admitted for other reasons. Methods: After IRB approval, the MarketScan Research Database was used to study individual-level healthcare claims data for the 2007 year. Patients with employer-based insurance for 12 continuous months and who were treated in the hospital for CDC were analyzed. A principle admission diagnosis of CDC during hospitalization was defined as primary CDC (PCDC), while secondary CDC (SCDC) was defined as contracting CDC while in the hospital for other reasons. Two-sample t-tests and z-tests were used for a comparison of means, Chi-square tests were used to test associations, and logistic regression was conducted to analyze 30-day and 60-day readmission rates for CDC.Results: A total of 4754 CDC patients were identified (PCDC: 2128 (45%); SCDC: 2626 (55%); p=005). PCDC patients were slightly younger than SCDC patients (45 years vs. 46 years; p=0.01) and were more likely to be male (PCDC: 67% male; SCDC: 55% male; p<0.0001). LOS was significantly longer for SCDC than PCDC (14.4 days vs. 5.2 days; p<0.0001). The major diagnostic code (MDC) for SCDC admissions was related to digestive system disorders (25%); by comparison, for all in-patients included in the database regardless of CDC status, only 9.4% had a primary admission MDC for digestive disorders. SCDC patients had a slightly greater mean Charlson comorbidity score (primary: 0.76; secondary: 1.29; p<0.0001). Mean total inpatient hospital payments were significantly higher for the SCDC group ($44,349 vs. $12,693; p<0.0001). Re-admission rates to treat CDC (Table 1) following PCDC were twice as high at 30-days and three times higher at 60-days compared to SCDC patients. Only 47.5% of PCDC patients received any antibiotic therapy (metronidazole and/or vancomycin) at the time of their first discharge, and only 26.4% of SCDC were provided discharge antibiotics. Conclusions: Among the study population, SCDC was more common and associated with greater hospital costs and longer LOS than PCDC. Admission to the hospital for digestive system disorders is associated with developing CDC. Readmission rates for subsequent bouts of CDC are two to three times as likely for PCDC. A surprisingly large percentage of patients are not provided with antibiotics at discharge, which helps explain the observed re-admission rates and may indicate a widespread under-treatment of the disease.
Readmission rates for Primary and Secondary C. difficile colitis

	PCDC	SCDC	p value
30-day Readmission Rates for CDC	5.5%	2.3%	<0.0001
60-day Readmission Rates for CDC	6.2%	2.8%	<0.0001
Patients Given Metronidazole and/or Vancomycin at First Hospital Discharge	47.5%	26.4%	<0.0001