Surgical site infections in cardiac surgery: risk factors, microbiological characteristics of causative pathogens

Aims: the aim of this study is to analyze the risk factors, the range of causative pathogens and their resistance to antibiotics in surgical site infections (SSIs) following coronary artery bypass surgeries. Objectives: 1. To calculate the incidence of SSIs following coronary artery bypass surgeries. 2. To determine risk factors for SSIs. 3. To evaluate the range of causative pathogens and their sensitivity to antibiotics. Methodology. This study involved a group of patients that underwent coronary artery bypass surgery between August and December of 2014 and between August and December of 2017. The surgeries were performed in the hospital of Lithuanian University of Health Sciences “Kauno Klinikos” (LUHS KK), department of cardiac surgery. A retrospective analysis was performed on the patients’ medical history records and microbiological test results. All data was gathered in a special surgical site infection surveillance data collection form approved by the Minister of Health of the Republic of Lithuania (annex 1). The data was then entered and coded in an electronic database of digital forms created with EpiData Entry 3.1 application (annex 2). All data was analyzed using Microsoft Office Excel and IBM SPSS Statistics 23.0. Mann-Whitney U test was used to compare the means of two independent samples, ANOVA F test was used to compare the means of three or more independent samples. Pearson correlation was used to analyze the linear relationship between two continuous variables. Chi-square (χ2) test was used to analyze the relationship between categorical variables. The difference between samples was considered to be statistically significant when p ≤ 0,05. Results. The study included data of 479 patients: 333 men (69,5 %) and 146 women (30,5 %). The mean age was 68,1 ± 9,19 years, with a median of 69 years. 320 (66,8 %) of the patients did not have any of the risk factors, 39 (8,1 %) patients had diabetes, 92 (19,2 %) patients were obese (BMI > 30), and 28 (5,8 %) were obese and had diabetes. The mean length of hospital stay was 21,3 ± 11,95 days. Most of the coronary artery bypass surgeries were performed using three or four and more grafts, respectively 200 (41,8 %) and 208 (43,4 %) cases, the mean duration of all performed surgeries was 206,24 ± 53,42 minutes. There were 343 (71,6 %) patients with ASA score of 3, 135 (28,2 %) patients with ASA score of 4 and only one (0,2 %) with ASA score of 5. 476 (99,4 %) patients were administered antibiotic prophylaxis. A total of 37 patients (7,7 %) developed SSIs, seven of them were caused by Staphylococcus aureus, Enterococcus faecalis, Pseudomonas aeruginosa and Serratia marcescens. The latter (S. marcescens) was resistant to ampicillin, ampicillin/sulbactam, cefuroxime, cefotaxime and ciprofloxacin. Conclusions. The overall incidence of SSIs following coronary artery bypass surgeries in the hospital of LUHS KK, department of cardiac surgery, was 7,7 %. No significant risk factors for SSIs were identified in this study. Male sex and longer duration of surgery were factors that could have had little significance for SSIs development in patients. Seven microorganisms were isolated, four of them were methicillin-sensitive S. aureus. Other isolated microorganisms were E. faecalis, P. aeruginosa and S. marcescens, which was resistant to ampicillin, ampicillin/sulbactam, cefuroxime, cefotaxime and ciprofloxacin