Standardized infection ratios for three general surgery procedures:: A comparison between Spanish hospitals and US centers participating in the National Nosocomial Infections Surveillance System

OBJECTIVES: To compare Spanish surgical wound infection (SWI) rates for three procedures with those published by the U.S. NNIS System, and to analyze quarterly trends. DESIGN: This was a 4-year prospective analysis of SWI using data from a Spanish nosocomial infection surveillance network based on CDC classification criteria. SWI rates were computed as standardized infection ratios (SIRs). Trends for both SWIs and SIRs were evaluated by linear regression. SETTING: Forty-three Spanish hospitals during 1997 through 2000. PATIENTS: Those undergoing cholecystectomy (n = 7,631), appendectomy (n = 5,780), and herniorrhaphy (n = 9,864). RESULTS: For cholecystectomy patients, the SWI rate was 4.38% and the SIR was 3.32. Both of these variables showed a slightly rising, although nonsignificant, linear trend during the study period. For appendectomy patients, the SWI rate was 7.94% and the SIR was 2.86. The linear trend was increasing for both, but only the SWI rate attained significance. For herniorrhaphy patients, the SWI rate was 1.77% and the SIR was 1.64. Both of these variables showed a significant descending tendency during the 4 years. CONCLUSIONS: Because the SIR takes into account the patient risk category, it is the best indicator of the trend shown by the SWI rate over time for a given surgical procedure. According to our comparison of SIRs with reference NNIS System values, SWI rates for cholecystectomy and appendectomy were high. Monitoring of the SIR will provide a basis for the design of infection control measures and the assessment of their effectiveness.