Risk factors for incisional surgical site infection after elective laparoscopic colorectal surgery

Abstract Background Surgical site infection (SSI) is a common morbidity in patients undergoing colorectal surgery, and the focus of previous studies has primarily been on incisional SSI. Most reports thus far have focused on open surgery rather than on laparoscopic colorectal surgery (Lap CR). Therefore, the aim of the present study was to identify the risk factors for incisional SSI in patients undergoing elective Lap CR. Methods This retrospective study was conducted to evaluate the occurrence and risk factors of incisional SSI for elective Lap CR. From January 2008 to June 2018, 1825 consecutive patients with a preoperative diagnosis of colorectal cancer who underwent Lap CR were analyzed at a single institution. Results Incidence of incisional SSI was 3.3%. Postoperative hospital stay (days) was significantly longer in the incisional SSI group than in the non‐incisional SSI group (8 [6‐12] vs 10 [8‐19], P < 0.001). Incisional SSI were significantly associated with five operative factors: blood loss (g) (P < 0.014), midline wound length (mm) (P = 0.038), suture materials (P = 0.014), suture technique (interrupted vs continuous mass closure, P = 0.003), and organ/space SSI (P = 0.041). Multivariate analysis showed that continuous mass closure (odds ratio 0.290; 95% confidence interval 0.101‐0.831, P = 0.021) was the only factor independently associated with the incidence of incisional SSI. Conclusions Incidence of incisional SSI was comparable to that in previous reports. Continuous mass closure decreased the risk of incisional SSI in elective Lap CR.

bacterial load in the associated organ/space. 3 Indeed, in open colorectal surgery, the incisional SSI rate reportedly ranges from 4.7% to 26%. [4][5][6] The risk factors of incisional SSI in colorectal surgery can be classified into patient-and operation-related factors. In general, the patient-related factors are considered to play a critical role in incisional SSI, and many have been identified thus far; 5,[7][8][9] however, most are difficult to manipulate.
Surgical techniques may be able to reduce the SSI rate, and ideal approaches have long been examined, including antimicrobial suture and methods of abdominal closure. [10][11][12][13][14] However, these previous reports have focused on open colorectal surgery, and there are few reports of risk factors for incisional SSI with laparoscopic colorectal surgery (Lap CR). In one report that investigated such risk factors, the number of cases was as small as approximately 400. 15,16 Over the past two decades, with the widespread application of Lap CR, the incidence of incisional SSI has decreased (2.7%-8.8%), 16,17 but incisional SSI associated with this technique remain a clinical problem to be solved. Therefore, the aim of the present study was to retrospectively evaluate the risk factors in patients undergoing elective Lap CR.

| Study design
The study protocol was approved by the Ethical Advisory Committee of Yokohama City University School of Medicine (B180400018).
From January 2008 to June 2018, a total of 1890 patients who underwent elective Lap CR at Yokohama City University Medical Center were retrospectively collected. Of these, 60 cases were excluded from the analysis because of conversion to open surgery, and five were excluded because of pelvic exenteration. The remaining 1825 patients were analyzed in this retrospective study (Figure 1).

| Antibiotic prophylaxis
During the induction of anesthesia, one dose of prophylactic i.v. antibiotics (cefmetazole 1.0 g) was given, and an additional dose was given every 3 hours during surgery and 8 hours after surgery. In cases with impaired renal function, we prolonged the dosage interval. Oral antibiotics were not used in bowel preparation.

| Operative approach
All operations were carried out or supervised by surgeons qualified under the Endoscopic Surgical Skill Qualification System of the Japan Society for Endoscopic Surgery. 18 Laparoscopic colorectal surgery was carried out using five ports: a 12-mm port in the umbilical region, 5-mm ports in the upper-right, left, and lower-left quadrants, and a 12-mm port in the lower-right quadrant. A 12-mm umbilical trocar was used as a camera port for a rigid scope. Central vessel ligation and colon or rectum mobilization were done laparoscopically. The specimen was extracted through the umbilical port, which was extended to approximately 2-5 cm. To avoid contamination, a wound protector was used in each case.

| Diagnosis of incisional SSI
All patients were monitored for postoperative incisional SSI, including superficial and deep SSI. Surgeons carried out a physical examination every day from the operating day until discharge. After hospital discharge, all patients were followed at the hospital as outpatients until day 30. Diagnosis of SSI was based on the definitions of the CDC guidelines: (i) purulent discharge with or without laboratory confirmation from the superficial incision; (ii) organisms isolated from an aseptically obtained culture of fluid or tissue from the superficial incision; (iii) at least one of the indicated signs or symptoms of infection (pain or tenderness, localized swelling, redness, or heat and superficial incision are deliberately opened by surgeon, unless the incision is culture-negative); and (iv) a diagnosis of superficial SSI by the surgeon or attending physician. 1 Using these definitions, incisional SSI were diagnosed in cases of such findings occurring within 30 days after surgery.

| Statistical analyses
Primary outcome of the study was to evaluate the risk factors for incisional SSI at the midline wound. Quantitative data are expressed as median and interquartile range (IQR). We used the Mann-Whitney U test to compare the median and IQR of continuous variables (such as age) and the χ 2 test or Fisher's exact probability test to compare the proportion of categorical variables (such as gender). P value of 0.05 or less was considered statistically significant.
Following the univariate analysis, those variables with a P value less than 0.1 were selected for the multivariate analysis using the logistic regression method.
All statistical analyses were carried out with EZR (Saitama Medical Center, Jichi Medical University, Saitama, Japan), which is a graphical user interface for R (The R Foundation for Statistical Computing, Vienna, Austria). More precisely, it is a modified version of R Commander designed to add statistical functions frequently used in biostatistics.

| RE SULTS
A total of 1825 patients were analyzed ( Figure 1). All surgical wounds were classified as clean-contaminated (bowel was opened without spilling contents; class 2). Incisional SSI was detected in 61 out of the 1825 patients (3.34%).

| Findings of the univariate analysis
In the univariate analysis, patients were divided into those with or without incisional SSI and compared. Table 1 shows comparisons of patient-related characteristics. None of the variables relating to patient-related factors was significantly associated with  Table 2 shows comparisons of perioperative/operative-related characteristics. Postoperative hospital stay was significantly longer in the incisional SSI group than in the non-incisional SSI group. In addition, incisional SSI was also significantly associated with five operative factors: blood loss (g) (P < 0.001), midline wound length (mm) (P = 0.038), suture materials (P = 0.014), suture technique (interrupted vs continuous mass closure, P = 0.003), and organ/space SSI (P = 0.041). Table 3 shows the results of the multivariate analysis. In this analysis, only continuous mass closure was significantly associated with a decreased risk of incisional SSI (odds ratio 0.290; 95% confidence interval 0.101-0.831, P = 0.021).

| D ISCUSS I ON
The purpose of the present study was to evaluate the risk factors of incisional SSI in elective Lap CR. We showed that no patient-related factors were associated with such SSI and that continuous mass closure significantly decreased their rate in our population.
Incidence of incisional SSI is multifactorial, and risk factors can be divided broadly into patient-and operation-related factors.
Patient-related factors have been considered to play a critical role in the occurrence of incisional SSI, and various risk factors have been identified, including obesity, malnutrition, smoking, and diabetes mellitus. 5,7-9 However, in our study, no patient-related factors were associated with incisional SSI. and postoperative glucose control. 31 Moreover, the incidence of incisional hernia is an important endpoint comparing closure methods, but the aim of the present study was to evaluate risk factors of incisional SSI only and we did not examine this. In another study, we are now investigating its rate in Lap CR.

Suture materials have been recognized as a potential breeding ground for infection. Sutures coated with antimicrobial
However, despite these limitations, this remains the first report of incisional SSI in a large number of Lap CR cases. Further prospective investigations will be needed to determine the risk factors of incisional SSI in elective Lap CR and the ideal closure method.

| CON CLUS ION
Incidence of incisional SSI was comparable to that in previous reports. Continuous mass closure of the midline fascia decreased the risk of incisional SSI in elective Lap CR.

D I SCLOS U R E
Authors declare no conflicts of interest for this article.