Surgical antibiotic prophylaxis: effect in postoperative infections

Objective: to assess the risk of surgical wound infection and hospital acqu ired infections among patients with and without adequate antibiotic prophyl axis. Also, to provide models to predict the contributing factors of hospit al infection and surgical wound infection. Design: survey study. Prospectiv e cohort study over 14 months, with data collected by a nurse and a epidemi ologist through visits to the surgical areas, a review of the medical recor d and consultation with the medical doctor and nurses attending the patient s. Setting: Two hundred and fifty bed, general hospital serving Puertollano (Ciudad Real), population - 50,000. Results: between February 1998 and Apr il 1999, 754 patients underwent surgery, 263 (34.88%) received appropriate peri-operative prophylaxis while 491 (65.12%) received inadequate prophylax is. For those who received adequate antibiotic prophylaxis, the percentage of nosocomial infection was 10.65% compared with the group who received ina dequate prophylaxis in which the percentage of nosocomial infection was 33. 40%. The relative risk of nosocomial infection was, therefore, 4.21 times h igher 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 wou nd 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 infect ion incorporated seven prognostic factors: age, length of venous periferic route, vesicle catheter, duration of operation, obesity, metabolic or neopl asm diseases and adequate or inadequate prophylaxis. When we incorporated t hese variables in the multi-factorial analysis we found that the relative r isk of developing nosocomial infection was 2.33 times higher in the group w hich received inadequate prophylaxis. When we applied the second logistic m ultiple regression model (wound infection), we discovered that the probabil ity of developing surgical wound infection was 2.32 times higher in the gro up which received inadequate prophylaxis as opposed to the group, which rec eived adequate prophylaxis. The goodness of fit (Hosmer-Lemeshow test) show ed a correct significance in all models. Conclusions: a multi-factorial ana lysis was applied to identify the high-risk patients and the risk factors f or postoperative infections. Through the application of these multiple regr ession logistic models, we conclude that the correct antibiotic prophylaxis is effective and will subsequently reduce postoperative infection rates, e specially in high-risk patients. Therefore, the choice of antimicrobial age nt should be made on the basis of the criteria of hospital committee.