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To identify factors associated with surgical wound infections, Lizan-Garcia and colleagues in Madrid conducted a prospective cohort study in a 1300-bed university-affiliated, tertiary care hospital, of 2237 patients undergoing general surgery procedures who had post-surgery stays of more than 48 hours. The patients were 48 ± 23 years of age and were hospitalized for 16 ± 14 days. Cholecystectomy, appendectomy, and herniorrhaphy were the most frequently performed procedures. Data were collected by nurses trained in epidemiology, who visited the units every two days and reviewed records and charts.
A total of 254 patients (11.4%) developed surgical wound infections. Odds ratios (OR) were estimated using unconditional multiple logistic regression. Eight factors were independently associated with risk of surgical wound infection: age (OR = 1.2 for every 10 years of age); wound classification (clean-contaminated, OR = 6.4; contaminated, OR = 3.7; dirty or infected, OR = 9.3); antimicrobial prophylaxis (OR = 0.5); stay prior to surgery (OR = 1.1 for every 3 days); duration of operation (OR = 1.5 for every 60 minutes); malignant neoplasm (OR = 1.7); emergency procedure (OR = 1.99); intensive care unit stay prior to surgery (OR = 2.6); and antimicrobial prophylaxis administered two or more hours before the operation (OR = 5.3).
Thus, in general, antibiotic prophylaxis protected against surgical wound infection (OR = 0.5). However, the number of surgical wound infections increased substantially if antimicrobial prophylaxis was not given within two hours of surgery. When antibiotic prophylaxis was not given within this two-hour time window, the risk of postoperative wound infection was increased by a factor of 5.3. (Lizan-Garcia M, et al. Infect Control Hosp Epidemiol 1997;18:310-315.)
The incidence of surgical wound infections has declined remarkably in the past 25 years, mainly because of the empirical use of antibiotics as prophylactic agents. However, all authorities do not agree on the timing of administration, choice of drug, or duration of administration. In general, antibiotic prophylaxis is now recommended for elective, clean surgical procedures where a foreign body is used, and in clean-contaminated procedures. Second-generation cephalosporins are typically administered intravenously prior to incision and additional doses are given only if the procedure lasts more than 3-4 hours (Holzheimer RG, et al. Infect Control Hosp Epidemiol 1997:18:449-456).
In this study, 50% of the patients who aquired a surgical wound infection received antibiotic prophylaxis, but the regimen was considered to have been incorrect for half the patients. An additional 11% of patients did not receive any prophylaxis, although this was recommended based on the hospital’s infection control committee guidelines. These findings are consistent with those of prior studies showing that antibiotic prophylaxis is administered according to recommendations in only about 80% of elective surgeries and approximately 70% of emergency surgeries. In some studies, the timing and duration of antibiotic prophylaxis has varied from 2-24 hours before the operation to up to 24 hours and more after the operation.
An encouraging finding from this research is that one of the factors that added most to the risk of postoperative wound infectiontiming of antibiotic administrationis very easy to correct. Unfortunately, the variable "antibiotic prophylaxis administered more than two hours before operation" was collected as a discrete variable, and it was therefore not possible to carry out a more detailed analysis of the relationship between prophylaxis administration times and the occurrence of surgical wound infections. This study was conducted in a population of general surgery patients, most of whom did not require management in an ICU. It would be interesting to know if similar findings would occur if the study had been conducted in critically ill patients or patients who required ICU admission following surgery.