Risk factors for postoperative infection.

During a 4-year period, we collected prospective epidemiologic data and intraoperative wound cultures from 1,852 surgery patients at a university-affiliated community hospital in order to identify the critical risk factors for postoperative wound infections and study the impact of perioperative antibiotics on the bacteriology of infected wounds. Stepwise logistic regression analysis revealed four risk factors that were independent of each other and highly predictive for subsequent wound infection. These were the surgical wound class, American Society of Anesthesiologists physical status grouping, duration of surgery, and results of intraoperative cultures. Addition of other variables to our model did not increase the predicted probability of infection. Even though patients with positive intraoperative cultures had an increased rate of infection, this information had limited clinical utility. The predictive value of a positive culture was low (32%), false-positive rate was high (82%), and concordance with isolates from infected wounds was low (41% when both cultures were positive). Patients who had received perioperative antibiotics and who developed infections were frequently infected with organisms that were resistant to the perioperative drug regimen, compared with patients who had not received antibiotics. A better understanding of the variables that affect the epidemiology and pathogenesis of postoperative wound infection will enable us to make more valid comparisons of rates among hospitals, help us to develop more effective infection control strategies and provide us with more effective treatments.