Assessing operative site infection in surgical patients

We evaluated the contribution of altered host defense to the risk of developing an operative site infection. In part 1 of this study, we measured the following variables in 404 preoperative patients: cutaneous delayed-type hypersensitivity, age, serum albumin level, contamination status at the time of surgery, and the duration of surgery. Patients were examined daily postoperatively for the presence of an operative site infection (culture-positive drainage or infected tissue; overall rate, 17.3%). The above variables, plus previously defined risk factors, were examined by logistic regression analysis using the development of an operative site infection as the dependent variable. An equation to calculate the probability of developing a postoperative wound infection was thus derived. In part 2 of the study, a separate, matched group of 404 preoperative patients was used to test the validity of this predictive equation. A good fit of the model was obtained, with 70.3 wound infections predicted and 67 obtained (chi 2 = 0.8; not significant, ie, no difference between expected and observed wound infections at all probability deciles). We conclude that there are three determinants of an operative site infection, host defense (delayed-type hypersensitivity), acute and chronic physiologic derangement (albumin and age) and bacterial contamination risk at surgery (contamination status and duration of surgery).