Standardized infection ratio: the next generation of risk-adjusted wound infection measures

Abstract

Abstract Background The scientific literature overwhelmingly supports the value of surgical site infection (SSI) surveillance with feedback of infection rates to surgeons. Recognizing that feedback has little value without some form of adjustment for patient factors, surgeons long ago developed the four-level wound classification system. In the 1980s the SENIC multivariate risk index was introduced, followed by the National Nosocomial Infection Surveillance multivariate risk index which is the currently recommended US standard. Methods To address recent advances in surgical technology, ambulatory surgery, and differences between the USA and other countries, newer risk-adjustment methods were explored. The ideal approach would overcome the following common practical problems encountered in generating SSI rates such as: (1) new patient-level risk factors, (2) technology-specific factors, (3) small monthly denominators and (4) postdischarge surveillance. Despite increased mathematical complexity, an acceptable risk-adjustment technique must still provide easily interpretable results. Results The standardized infection ratio (SIR) is proposed as the next generation in epidemiological approaches for monitoring and feeding back risk-adjusted SSI rates to surgeons. The SIR is a single monthly number for each surgeon, calculated by dividing the observed number of SSIs by the expected number predicted from a complex statistical model of patient-level and technology-specific risk factors. Like the well known standardized mortality ratio, the SIR offers the advantage of providing one generalizable quality index regardless of the mix of operations performed. In addition, the SIR is well suited to control chart techniques and for providing valid interhospital comparisons. Conclusion The SIR model offers simple data input and easily interpretable output suitable for application in all healthcare settings worldwide.