The effect of increasing age on the risk of surgical site infection.

BACKGROUND An increasing number of older persons undergo surgery, but the relationship between increasing age and risk of surgical site infection (SSI) has not been established. The objective of the present study was to determine the relationship between increasing age and risk of SSI. METHODS The present cohort study included patients who underwent surgery between February 1991 and July 2002. Patients >17 years of age were divided randomly into derivation and validation cohorts. The study was conducted at 11 hospitals. SSIs were prospectively identified by use of Centers for Disease Control and Prevention criteria. RESULTS The study included 144,485 consecutive surgical patients and 1684 SSIs (rate of SSI, 1.2%). There were 72,139 procedures and 873 SSIs in the derivation cohort. Adjusted analyses revealed a significant relationship between age and risk of SSI (P=.006). Risk of SSI increased by 1.1%/year between ages 17 and 65 years (P=.002). At age >/=65 years, risk of SSI decreased by 1.2% for each additional year (P=.008). There were 72,334 procedures and 811 SSIs in the validation cohort. The relationship between age and risk of SSI was similar in the validation cohort. CONCLUSIONS Increasing age independently predicted an increased risk of SSI until age 65 years. At ages >/=65 years, increasing age independently predicted a decreased risk of SSI.