Surgical site infections in patients undergoing major operations in a university hospital: using standardized infection ratio as a benchmarking tool

BACKGROUND: Because patterns of infection acquired in patients undergoing operation are ever changing, it is an essential part of nosocomial infection surveillance programs to periodically document the epidemiologic features of infection in these patients. This study was conducted with the primary intention of describing the incidence and risk factors of the surgical site infection (SSI). METHODS: We performed a prospective study in patients undergoing certain major operations at a 750-bed university hospital in Thailand. The National Nosocomial Infection Surveillance (NNIS) system method and criteria were used for identifying and diagnosing infection. The infection rates were benchmarked with the NNIS report by means of indirect standardization and reported in terms of standardized infection ratio. Risk factors for SSI were evaluated using the multiple logistic regression model. RESULTS: From September 1998 to March 2000, the study included 4193 patients with 4437 major operations. The study identified 192 SSIs, 76 urinary catheter-related urinary tract infections, 26 central line-related bloodstream infections, and 39 instances of ventilator-associated pneumonia (VAP), yielding an infection rate of 4.3 SSIs/100 operations, 11.0 catheter-related urinary tract infections/1000 urinary catheter-days, 6.1 central line-related bloodstream infections/1000 central line-days, and 11.0 VAPs/1000 ventilator-days. When compared with data from NNIS, the standardized infection ratio of SSI, catheter-related urinary tract infection, central line-related bloodstream infection, and VAP were 2.3, 2.1, 1.1, and 0.8, respectively. The factors that significantly associated with SSI were duration of operation in minutes, American Society of Anesthesiologists (ASA) class, and degree of wound contamination. CONCLUSION: All of the infection rates identified, except VAP, were higher than the average NNIS rates. The risk factors for SSI were prolonged duration of operation, poor physical status according to ASA classification, and higher degree of wound contamination.