SSI is a common complication after colon surgery that causes patients to be involved with its complications and costs [16, 17]. Due to bacterial load and possible contamination during or after surgery, patients undergoing colon surgery are at high risk for SSI [18].Therefore, knowing the status of SSI in surgical patients and identifying the factors associated with the occurrence of SSI is of particular importance. To date, this study is one of the first studies on the incidence of SSI in northeastern Iran conducted at a colorectal referral center. Overall, in this study, we identified 56 cases (23.33%) of SSI among 240 cases of colon cancer surgery. In different studies, the results show that the incidence of SSI ranges from 3.6% [19] and 3.3% [20] to 32.1% [20], which may be due to the fact that in some studies the definition of SSI is different. Also, the period of time that patients are followed is different in each study [21–23]. It should be noted, however, that there are studies around the world that, despite having a single definition of SSI based on the CDC definition, have reported different incidence (3.3–19.9%) [20, 24–26]. By standard definition, the results of our study reported a higher incidence of SSI than many other studies. Different factors affect these differences. The first is the type of hospital where the surgery was performed. So that in most cases, the lower reported SSI rate is related to specialized hospitals, while the hospital we are studying is a governmental and educational hospital, in most cases, the surgeries were performed by students who are less skilled. The second reason for the lower reporting of SSIs in other studies is that their study is multicenter, which makes the overall incidence lower. Finally, in some studies, the study is limited to a specific type of SSI; for example, only on the complex type (deep incisional or organ-space) or the superficial type [27, 28], while our study did not distinguish between them and reported in general. Therefore, these are the cases that partially justify these differences between the findings.
The most important findings of this study were that corticosteroid use, type of surgical intervention, preoperative anemia, diabetes and opium use were the risk factors for SSI after colon surgery.
Analysis of the data from this study showed that the incidence of SSI was higher in people who took corticosteroids than in those who did not take corticosteroids. Thus, corticosteroids increase the risk of SSI up to 3 times. There have not been many studies on the effect of corticosteroids on SSI after colon surgery. However, a study by Lieber et al. [29] that examined the effect of corticosteroids on SSI after cranial surgery showed that corticosteroids could nearly double the chances of developing SSI (OR = 1.86, 95 % CI 1.03–3.37,) which is consistent with the findings of our study. The variables related to individuals of the subjects in our study, including age and sex, did not show a significant relationship with the incidence of SSI. However, in a few other studies, age was a risk factor for SSI in other surgeries [30], but in most studies for SSI, colonic surgery was not observed [22, 23, 28, 31, 32]. An interesting relationship observed in this study was that with increasing age (over 60 years) the risk of developing SSI decreases, although this relationship was not significant. In the study of Tie-Ying et al. [24], similar to the result of our research, such a result was obtained. Our study showed that the type of intervention for colon cancer was significantly associated with SSI, so that patients who had segmental resection with anastomosis had more than twice the risk of SSI compared to patients who had right hemicolectomy. Contrary to our study, the study of Marta et al. [26] did not show a significant relationship between the type of intervention and the incidence of SSI. One of the reasons that can justify these differences is that in other studies [20, 33] there is more variety of interventions, but in our study only three interventions for colon cancer have been considered. Therefore, although the results of our study have shown a significant impact of the type of intervention, however, due to the contradictory results in other studies, further investigation is needed. In our study, it was found that anemia before colon surgery is one of the risk factors for SSI, so people with anemia were more than 4 times more likely to develop SSI. In the study of Pu-Run Lei et al., Anemia was one of the risk factors for SSI (OR: 4.591; 95% CI: 2.567–8.211). The study by Marta et al. [26] also showed that not having anemia significantly reduced the risk of SSI (OR = 0.50 95% CI: 0.29–0.89).
According to the results of our study and the results of other studies, preoperative anemia can have an independent effect on the incidence of SSI.
Many studies have shown that the incidence of SSI was higher in people with diabetes, but this incidence was not statistically significant in diabetic patients [
24,
25,
33–
35]. However, our study found that having diabetes significantly increased the risk of developing SSI more than doubled. Therefore, the results of the study by Marta et al. [
26] confirm the findings of our study to some extent (OR = 1.85; 95% CI: 1.04–3.24).
According to the results presented in various studies that show inconsistencies in the results, the relationship between diabetes and the incidence of SSI is not clear and it is necessary to examine this relationship in an epidemiological study with good methodology or meta-analysis.
Another factor that has received less attention in other studies is the effect of drug use or addiction on the incidence of SSI in patients who have undergone surgery. However, our study examined the association between opium use and the incidence of SSI and found that opium use can significantly increase the risk of SSI by nearly two-fold. Another study by Pirkle et al. [
36] on chronic opioid use showed that the risk of developing SSI in this group was significantly higher. It should be noted, however, that in most postoperative surgeries, opioids are usually prescribed to reduce pain, so showing this association will be complex and require further investigation into addicts or drug users.
In this study, patients were followed up after 30 days of discharge from the hospital through telephone interviews or review of readmission records. Data from patients who were lost in follow-up were not included in the study.
Our study has several limitations. First, this study was concentrated on colon surgery in a referral hospital; therefore, similar results may not be obtained in other populations, specialties, or hospitals. Secondly, some details should be considered before designing a study, including: blood pressure, blood sugar, dose of uses of drugs, type of wound, and adhesive incise drapes.