The Case For A Population Standardized Infection Ratio (Sir): A Metric That Marries The Device Sir To The Standardized Utilization Ratio (Sur)

Background: The device standardized infection ratio (SIR) is used to compare unit and hospital performance for different publicly reported infections. Interventions to reduce unnecessary device use may select a higher-risk population, leading to a paradoxical increase in SIR for some high-performing facilities. The standardized utilization ratio (SUR) adjusts for device use for different units and facilities. Methods: We calculated the device SIR (calculated based on actual device days) and population SIR (defined as sigma observed events divided by sigma predicted events based on predicted device days), adjusting for the facility SUR for both central-line-associated bloodstream infections (CLABSIs) and catheter-associated urinary tract infections (CAUTIs) in 84 hospitals from a single system for calendar years 2016 and 2017. Results: The central-line SUR was 1.02 for 801,172 central-line days, with a device SIR of 0.76 and a population SIR of 0.78, a 1.6% relative increase. On the other hand, the urinary catheter SUR was 0.90 for 757,504 urinary catheter days, with a device SIR of 0.84 and a population SIR of 0.76, a 10.0% relative decrease. The cumulative attributable difference for CAUTI to a target SIR of 1 was -135.4 for the device SIR compared to -203.66 for the population SIR, a 50.8% increase in prevented events. Conclusion: Population SIR accounts for predicted device utilization; thus, it is an attractive metric with which to address overall risk of infection or harm to a patient population. It also reduces the risk of selection bias that may impact the device SIR with interventions to reduce device use.