Surgical Site Infections after Colon Surgery: What the SIR Doesn’t Tell You

Abstract

BackgroundThe National Healthcare Safety Network (NHSN) complex 30 day surgical site infection (SSI) model uses diabetes, American Society of Anesthesiology (ASA) score, gender, age, body mass index (BMI), closure technique and oncology hospital status to determine the standardized infection ratio (SIR) for SSI after colon surgery in adult patients. This is an improvement over past models, but we hypothesized that this model still overlooks non-modifiable patient factors such as inflammatory bowel disease (IBD).MethodsWe identified all colon surgeries from the first quarter of 2013 through the third quarter of 2016 reportable to NHSN. Each case had a SSI risk score based on the NHSN SIR between 0 and 1. Patient billing data was used to identify International Classification of Disease (ICD) 9 and 10 codes pertinent to the Charlson comorbidity index (CCI) and IBD. The risk of SSI for IBD patients vs. others was calculated using Chi-squared analysis and multivariate models adjusting for CCI as well as the NHSN colon surgery model.ResultsIn univariate analysis NHSN risk score, CCI score and IBD were strongly associated with SSI. After adjusting for CCI and NHSN, alone or in combination, IBD remained significantly associated with risk for SSI.ConclusionIBD is a non-modifiable risk factor for SSI after colon surgery that is not accounted for in the NHSN model. In addition, the significant of the CCI suggests there may be other patient factors contributing to SSI risk. Further investigation to assess the significance of IBD and other comorbidities and risk factors is warranted. Hospitals that care for more complex patients may be unfairly penalized under the current NHSN modelTable:Colon Surgery SSI Risk FactorsVariableMean (SD) or n(%) for episodes without SSI (N = 4588)Mean (SD) or n(%) for episodes with SSI (N = 245)ORP valueNHSN model0.03 (0.01)0.03(0.01)0.02CCI score5.47 (3.69)6.13 (3.93)0.01IBD576 (12.55%)49 (20%)1.74 (1.26–2.41)<0.01IBD adjusted for CCI2.19 (1.54–3.09)<0.01IBD adjusted for NHSN1.73 (1.23–2.42)<0.01IBD adjusting for NHSN, CCI*2.19 (1.51–3.12)<0.01*Modified CCI eliminating age, diabetes components to minimize colinearity with NHSN scoreDisclosures All authors: No reported disclosures.