title: The standardized incidence ratio as a reliable tool for surgical site infection surveillance.
abstract: OBJECTIVE
  To evaluate whether the standardized incidence ratio (SIR) is a more reliable tool for comparing rates and temporal trends of surgical site infection (SSI) in surgery wards than the incidence rate among patients with an National Nosocomial Infections Surveillance system (NNIS) risk index category of 0.
  
  
  METHODS
  Observational, prospective cohort study in a sequential SSI surveillance system.
  
  
  METHODS
  Volunteer surgery wards in a surveillance network in northern France that annually conducted SSI surveillance for 3 months from 1998 to 2000.
  
  
  METHODS
  The incidence rate was the number of SSIs divided by the number of patients included, stratified by the NNIS risk index category. SIR was the observed number of SSIs divided by the expected number computed using a multiple regression model.
  
  
  RESULTS
  Overall, 26,904 patients in 67 surgery wards were enrolled. Between 1998 and 2000, the SSI incidence rate among patients with NNIS risk index category 0 decreased from 2.1% to 1.4%, which was a 33% reduction (P=.002). The SIR decreased from 1.2 (95% confidence interval [CI], 1.1-1.3) to 0.8 (95% CI, 0.7-0.9), which was a 20% decrease per year and an overall 33% reduction. The number of SSIs was significantly higher than expected in 17 of 201 surveillance periods over the 3 years. The classification of the wards according to the 2 indicators over the 3 years showed that wards with a high SIR did not consistently have the highest SSI incidence rate among patients with NNIS risk index category 0, partly because the type of surgical procedure and the duration of follow-up are not taken into account in the NNIS risk index.
  
  
  CONCLUSIONS
  SIR should be considered a reliable indicator to estimate the reduction in SSI incidence that results from implementation of infection control policies and for comparison of SSI rates between wards.
authors.affiliation: Interregional Center for the Coordination of Nosocomial Infection Control, Paris, France. christophe_rioux@hotmail.com
authors.forename: Christophe
authors.initials: C
authors.lastname: Rioux
authors.forename: Bruno
authors.initials: B
authors.lastname: Grandbastien
authors.forename: Pascal
authors.initials: P
authors.lastname: Astagneau
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D003428:Cross Infection / Q000453:epidemiology*; D005260:Female; D006801:Humans; D015994:Incidence; D017053:Infection Control / Q000379:methods / Q000592:standards*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011159:Population Surveillance / Q000379:methods; D011446:Prospective Studies; D040442:Public Health Informatics / Q000458:organization & administration; D012015:Reference Standards; D018570:Risk Assessment; D013530:Surgical Wound Infection / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control