Above and Beyond Individual Exposure: Ward-level Antibiotic Prescribing Is the Principal Predictor of Increased Clostridium difficile Infection (CDI) Risk
Background: Recent research on Clostridium difficile transmission suggests that exposure to spores from symptomatic patients may not completely explain hospital-acquired infections. Antibiotic exposure has been shown to be a primary risk factor for not only C. difficile infection (CDI), but also for asymptomatic colonization with C. difficile. In this study, we sought to discern the relative impacts of individual-level and ward-level antibiotic exposure on patient risk.
Methods: A cohort study design was used to assess the association of antibiotic exposure with the incidence of CDI among patients admitted to Sunnybrook hospital in Toronto, Canada. The source cohort consisted of all patients over 18 years old, without a previous CDI diagnosis, and hospitalized in an acute care ward at Sunnybrook hospital in a period spanning June 1, 2010 to May 31, 2012 (n=47,241).
Results: Across wards, patients received antibiotics for 22% to 58% of days. We found that ward-level prescribing was strongly associated with increased CDI risk. Based on weighted linear regression, each 10% increase in ward-level ABx prescribing was associated with a 3.9 per 1,000 patient-days (95% CI: based on weighted linear regression: 2.1 to 5.6, p < 0.001) increase in CDI incidence, and explained 56% of ward level variation in CDI rates (Figure). In multilevel Poisson analyses controlling for time since admission, age, individual-level antibiotic receipt, previous hospitalizations, infection pressure, and ICU admission, ward-level antibiotic prescribing was the strongest predictor of CDI risk. Each 10% increase in ward-level ABx prescribing was associated with a doubling of risk (RR = 1.83, 95% CI: 1.42 to 2.35); adjusted risk in the highest prescribing wards was thus 6 times higher (RR=6.13, 95% CI: 2.86 to 12.98) than risk in the lowest prescribing wards. In comparison, individual-level exposure was associated with only a doubling of risk (RR=2.06, 95% CI: 1.37 to 3.10).
Conclusion: Although many studies have considered the impact of individual-level risk factors on CDI, we found that ward-level antibiotic prescribing better explains CDI risk, and this suggests that asymptomatic colonized patients may be driving infection spread. This research has major implications for infection control, hospital hygiene, and antimicrobial stewardship.
D. N. Fisman, None