Surgical site surveillance and standardized infection ratios in an orthopedic specialty hospital

Abstract

BACKGROUND: Surgical site infection (SSI) surveillance data is an essential part of infection control programs. Benchmarking data against the National Nosocomial Infections Surveillance System (NNIS) system has been used since 1999 to evaluate SSI in an orthopedic specialty hospital. The presentation of this data is intended to demonstrate trends and risk factors associated within this patient population. METHODS: NNIS criteria were used to classify SSI in orthopedic surgery as superficial, deep, and organ/space. The infection rates were benchmarked with the NNIS report by stratifying total hips, total knees, spinal fusions, and laminectomies by risk factors 0, 1, 2 and 3 (ASA score, duration of operation, and degree of wound contamination). The expected versus actual number of infections, the infection rate, the standardized infection ratio, and probability value were calculated. RESULTS: From fiscal year (FY) 1999 through FY2004, there were 26,202 orthopedic cases with 229 SSIs (0.9%). In FY2004, data were stratified by type of surgery and showed the following infection rates: total hips, 0.3; total knees, 1.0; laminectomies, 0.9; and spinal fusions, 2.0. The standardized infection ratio (the number of infections divided by the expected number of infections) for each group was 0.2, 0.7, 0.8 and 0.9, respectively. Stratification by risk factors (SIR) for each category demonstrated an increased rate in spinal fusions in patients with greater 2 and 3 risk factors (9.3, as compared to the NNIS threshold of 6.3). An investigation revealed additional risk factors in this group: obesity, diabetes, and allograft implantation. Control measures were implemented and infection rates were reduced. CONCLUSION: SSI surveillance in an orthopedic specialty hospital analyzed over a 6-year period has demonstrated rates below NNIS benchmarking using SIR and probability values. The analysis of data in this manner is useful to detect specific problems and focus investigative activities.