Surgical antibiotic prophylaxis: effect in postoperative infections

Objective: to assess the risk of surgical wound infection and hospital acquired infections among patients with and without adequate antibiotic prophylaxis. Also, to provide models to predict the contributing factors of hospital infection and surgical wound infection. Design: survey study. Prospective cohort study over 14 months, with data collected by a nurse and a epidemiologist through visits to the surgical areas, a review of the medical record and consultation with the medical doctor and nurses attending the patients. Setting: Two hundred and fifty bed, general hospital serving Puertollano (Ciudad Real), population – 50,000. Results: between February 1998 and April 1999, 754 patients underwent surgery, 263 (34.88%) received appropriate peri-operative prophylaxis while 491 (65.12%) received inadequate prophylaxis. For those who received adequate antibiotic prophylaxis, the percentage of nosocomial infection was 10.65% compared with the group who received inadequate prophylaxis in which the percentage of nosocomial infection was 33.40%. The relative risk of nosocomial infection was, therefore, 4.21 times higher in the latter group (confidence intervals 95%: 2.71–6.51). A patient in the inadequate prophylaxis group had a 14.87% chance of wound infection while a patient in the adequate prophylaxis group had a 4.56% chance of wound infection. The relative risk of wound infection was 3.65 times higher in the group that received inadequate prophylaxis (confidence intervals 95%: 1.95–6.86). The final regression logistic model to assess nosocomial infection incorporated seven prognostic factors: age, length of venous periferic route, vesicle catheter, duration of operation, obesity, metabolic or neoplasm diseases and adequate or inadequate prophylaxis. When we incorporated these variables in the multi-factorial analysis we found that the relative risk of developing nosocomial infection was 2.33 times higher in the group which received inadequate prophylaxis. When we applied the second logistic multiple regression model (wound infection), we discovered that the probability of developing surgical wound infection was 2.32 times higher in the group which received inadequate prophylaxis as opposed to the group, which received adequate prophylaxis. The goodness of fit (Hosmer–Lemeshow test) showed a correct significance in all models. Conclusions: a multi-factorial analysis was applied to identify the high-risk patients and the risk factors for postoperative infections. Through the application of these multiple regression logistic models, we conclude that the correct antibiotic prophylaxis is effective and will subsequently reduce postoperative infection rates, especially in high-risk patients. Therefore, the choice of antimicrobial agent should be made on the basis of the criteria of hospital committee.