Risk Factors for Developing Surgical Wound Infection following Coronary Artery Bypass Graft Surgery, in Armenia: A Case Control Study

Abstract

Background: Sternal and leg wound infections following coronary artery bypass graft surgery (CABG) surgery are risk factors for increased morbidity and mortality as well as cost of treatment. It is estimated that the average cost of maintaining a patient in the hospital with a sternal wound infection is three times higher than the cost of maintaining a patient with an uncomplicated postoperative result. Deep sternal wound infection has been reported to occur in 1% to 4% of patients after CABG and carries a mortality of nearly 25%. Surveillance of surgical site infection (SSI) in hospitals in England between October 1997 and September 2002 showed that 4.3% of the patients developed SSI following CABG. According to a study conducted from 2003 to 2006 in Nork-Marash Medical Center (NMMC) in Yerevan, Armenia, the incidence of wound infections after CABG in NMMC was 7.4%. Objective: The overriding objective was to assess the combined effect of risk factors for developing wound infection following CABG, controlling for potential confounders. Design: A retrospective unmatched case-control study was conducted. Data were abstracted from medical records. Study population: The CABG patient population from Nork-Marash Medical Center who underwent CABG from January 1, 2006 through March 31, 2009. Results: The sample size was 801 (128 cases and 673 controls). The overall wound infection rate over the course of the hospital stay was 7.5% (128/1704). Among wound infection cases with reported sites of infection (out of 128 cases, seven were missing data on site of infection), the percent of patients developing chest infection alone was 65.3(79/121) %, the percent of developing leg infection alone was 28.9(35/121) %, and 5.8(7/121) % of patients developed both chest and leg infections. Staphylococcus Epidermitis (59.2% out of all cases), Staphylococcus Aureus (23.1%) and Escherichia Coli (12.9 %) were the most common infectious pathogens. The mean age of participants was 57 years. About 86% of all participants were male. The mean duration of operation was 4.3 hours, the mean duration of artificial breathing time was 23 hours and the mean duration of stay in the intensive care unit (ICU) was 67 hours. Bivariate analysis found that the unadjusted OR for developing SSI among those having diabetes compared to not having diabetes was 2.93 (95% CI: 1.9-4.4), the unadjusted OR for females as compared to males was 2.3 (95% CI: 1.4-3.8), and for those using versus not using inotropic drugs was 2.39 (95% CI: 1.3-4.2). Bivariate analysis of continuous variables showed that BMI (p-value <0.001), duration of operation (p-value<0.001), artificial breathing time (p-value <0.001), intubation time (p-value <0.001, duration of stay in the ICU (p-value <0.001), and blood glucose level (p-value <0.001) were associated with increased risk for developing wound infection following CABG. The final predictive multivariate model found the likelihood of developing wound infection was higher among those who had longer duration of operation, longer duration of stay in the ICU, who had diabetes, higher BMI and were female. A statistically significant interaction included in the final model was found between duration of operation and duration of stay in ICU (p=0.018), an interaction which suppressed their individual combined effects. Conclusions: Important predictive risk factors for increased risk of wound infection following CABG were longer duration of operation and stay in the ICU, diabetes, higher BMI and being female. Further research is needed to evaluate monthly/seasonal effects on rates of CABG wound infections and to evaluate rare risk factors utilizing larger sample sizes.