Blue Ribbon Abstract Award: Hospital-Acquired Clostridium difficile-Associated Disease: Differences in Definitions Translate into Large Differences in Rates

BACKGROUND/OBJECTIVES: Hospitalization is a major risk factor for Clostridium difficile (C. diff)-associated disease (CDAD). A traditional definition of hospital-acquired infection is onset greater than 48 hours after admission. A high number of previously hospitalized patients (pts) are diagnosed with CDAD within 48 hours of admission to our 1400 bed tertiary care teaching hospital. An expanded definition of hospital-acquired CDAD was tested, including pts with CDAD diagnosed within 48 hours of admission who were hospitalized in the previous 60 days. METHODS: All pts with diarrhea who tested positive for C. diff toxin A/B from 1/04 through 12/05 and were admitted to one of three general medicine floors were identified using electronic medical records. Cases were categorized by which definition of hospital-acquired CDAD they met. Repeat positive assays within 45 days were considered recurrent and excluded. Time to onset was calculated from admission date for cases meeting the traditional definition or from discharge date of the prior hospitalization for cases that met the expanded definition. Chi-square analysis was used to determine statistical significance. RESULTS: Using the traditional definition, including only patients who are diagnosed more than 48 hours after admission, rates for all three units were comparable (unit A: 57 cases/31,221 pt days, rate = 1.8; unit B: 54 cases/31,827 pt days, rate = 1.7; unit C: 37 cases/29,485 pt days, rate = 1.3), p = 0.18 for the difference between each unit. Using the expanded definition, rates increased by at least half (unit A: 27 additional cases, rate = 2.7, p = .02 for the difference between definitions for unit A; unit B: 43 additional cases, rate=3.0, p < .01; unit C: 30 additional cases, rate = 2.3, p < .01). The average time to onset of disease using the traditional definition was 9.9, 11.7, and 8.1 days for units A, B and C, respectively. Average time to onset for patients diagnosed within 48 hours of admit and hospitalized within the previous 60 days was 20.0, 20.0, and 16.7 days, respectively. Combining these cases to meet the expanded definition, the average time to onset becomes 13.1, 15.4, and 11.9 days for units A, B, and C, respectively. CONCLUSIONS: Using this expanded definition, the amount of hospital-acquired CDAD increases significantly. The traditional definition greatly underestimates the burden of CDAD. We intend to use the expanded definition for CDAD surveillance at our institution to better capture true incidence.