IH repair is traditionally regarded as a clean wound operation. However, the reported rate of SSI following IH repair varies widely in the literature, with most indicated higher than the defined value for a clean operation (an infectious rate < 2%) [8]. Identification of risk factors for SSI would be helpful to reduce infection rate by modification of those factors amenable to intervention. A few studies have reported that up to 60% of SSIs could be prevented by adopting strategies that include some evidence-based measures [15]. On the other hand, antibiotic prophylaxis is a usually accepted and recommended method for the prevention of SSI owing to its good activity and adequate concentration against potential pathogenic bacterium, but it also comprises risks of allergic side effects, bacterial resistance and increased costs [16]. The discussion on risk factors in our study may help to identify some unmodifiable factors used to select the best candidates for antibiotic prophylaxis. We excluded the patients receiving antibiotic prophylaxis in order to ensure the homogeneity of the data. Since the use of prosthetic material has become the rule nowadays, we focused our study only on mesh repair.
Controllable factors
Elevated BMI is associated with poor wound healing and increased incidence of SSIs, which has been reported by numerous other authors [17–19], possibly because of its relationship with other comorbidities, longer operation times, greater bleeding, and decrease in peri-operative subcutaneous tissue oxygenation [20].The larger impact of elevated BMI for superficial SSI than that for deep SSI could be explained mainly by the potential for dead spaces which may harbor fluid collections and infection during wound closure [21]. This may be similar cause leading to our own findings (all SSIs observed here were superficial). Although weight loss should be included in the list of optimization measures ahead of elective surgical intervention according to the available evidence, there has been no consistent appropriate range of BMI in the literature. In a large case series with 57,951 initial open IH repair based on the USA personal use file database, an BMI ≥ 35 kg/m2 was found to be an independent risk factor for SSI [22]. However, H. Yang et al. came to a conclusion that patients with a BMI > 25 kg/m2 had an increased risk for mesh infection following IH repair than those with a normal BMI from their 10-year experience in one Chinese center [23]. A BMI > 25 kg/m2 was also observed to be significantly associated with SSI in a Sweden’s study carried out in 2010 [11]. The different cut-off values for BMI may be explained by the differences in study population and study year. WHO has recommended lower BMI cutoffs for the definition of obesity and clinical preventive measures among Asians, in view of Asians being at higher risk of BMI related comorbidities at lower BMI cutoffs compared to international standards [24]. Coinciding with the study of H. Yang et al., we recommended that BMI should be kept within the range of 18.5–24.6 kg/m2 so as to decrease SSIs rate. Further exhaustive studies with a larger sample size are needed to develop a predictive model effectively to confirm the warning value of BMI.
Patients in our study who were current smokers had a 4.2-fold increased risk of superficial SSIs. The effect of patient smoking on SSI was previously discussed in the literature [18, 25, 26]. Smoking is known to increase tissue hypoxia via vascular vasospasm and a global increase in systemic inflammation [27]. Hypoxia promotes the colonization of bacteria and breaks oxidative bacterial killing mechanisms thus making the tissue vulnerable to infection [28]. Additionally, the temporary detrimental vasoactive effect on peripheral tissue blood flow induced by smoking may lead to infection developing in tissues characterized by a marginal blood supply [29] such as superficial SSIs which were found in our study. Antioxidant supplement such as vitamin C or/and vitamin E may attenuate the injury of smoking on inflammatory cells and endothelial function. Moreover, abstinence from smoking with the duration of at least 4 weeks preoperatively may decrease SSIs through the amelioration of inflammatory cell function and host defense, which has been revealed in several RCTs [30, 31]. It was not clear how smoking cessation affected SSI in our study because we lacked accurate data of each patient’s quit-smoking status. However, the recorded smoking cessation (range, 1-10yearspreoperatively) information of 116 patients were all found in no-SSI group.
Non-controllable risk factors
Interestingly, our study found that a higher NLR may be related to a raised risk of SSI. To our knowledge, higher NLR as a risk factor has not been identified associated with mesh repairs of IH previously. The development of SSIs has been believed to be related to the impairment of the immune system through systemic inflammation [32]. Colonized bacteria may begin to replicate and adhere to the surgical wounds if the host’s immune response is not sufficient to overcome the bacteria’s effect. NLR is one of the commonly used and convenient inflammatory markers that reflect this immune response [33], and it has been applied for the prediction of SSI in patients after several surgical operations such as colorectal[34], total knee arthroplasty [35], lumbar spinal[36], and head and neck cancer[37]. Yombi JC et al. found that NLR was a superior biomarker than C-reaction protein (CRP) to be included in the follow-up of early infectious complications after total knee arthroplasty, because it had a faster normalization than CRP [35]. Similarly, in the report of Deniz Bolat et al [38], NLR was noted as a potential laboratory value for predicting early penile prosthesis implant infection. The relationship between early SSI development (within 30 days postoperatively) and higher NLR that revealed in our study is corroborative of those reported in previous papers. Moreover, we observed a negative correlation between the preoperative NLR level and the postoperative period of SSI, further confirming higher NLR as a risk factor for SSI. A converse conclusion came from the literature - a lower preoperative NLR level tended to have a higher incidence of postoperative failure of incision healing - based on the following pathomecha-
nism: neutrophils played an important role on bactericidal action and the purification of necrotized tissues upon injury; the exhaustion and insufficiency of neutrophils may lead to the appearance of excessive abnormal fibrin of granulation tissue in the wound and the inhibition of granulation tissue’s formation [39, 40].
Our findings revealed that using a cut point of > 1.97, preoperative NLR level predicted postoperative SSI with a high sensitivity (74.4%) and specificity (51.8%). This cut-off was within the reported normal reference intervals for NLR (0.88-4.0) [36]. The similar normal threshold of preoperative NLR level in predicting postoperative SSI was also found in the study of Josse JM et al (≥ 2.3) [34] and Son HJ et al (≥ 2.9) [37]. A lower threshold may help to find out the surgical patients with intermediate risk of postsurgical SSI, who could not be usually identified early. The NLR may be an useful tool in the befitting preoperative treatment planning, conjuncting with standard perioperative risk assessment, with the aim to alleviate the occurrence or severity of a prospective adverse event.
Platelets are rich in proinflammatory agents and are possible to release highly active microparticles. PLR has been accepted as indicator revealing shifts in PLT and LYM counts due to acute inflammatory. Increasing evidence has suggested that PLR can afford valuable information to clinicians when encountering some infection related diseases, such as chronic obstructive pulmonary disease, rheumatic diseases and diabetic foot infection [41–43]. NLR negatively correlated with the postoperative period of SSI in our study, but it was not an independent risk factor for SSI by multivariate analyses, possibly due to the relative small number of infections identified here.
The open technique was also associated with increased SSI following mesh repairs of IH. Laparoscopic approach seems to be preferable in terms of risk for both superficial SSI and mesh infection [44]. The analysis of registry data in Germany showed a 0.1% superficial SSI rate and a 0.06% deep infection incidence in laparoscopic IH repair [45]. On the contrary, they recommende-
d antibiotic prophylaxis to be administered for open IH repair for its watchful SSI rate. The overall SSI rate was found to be significantly lower for laparoscopic than for the open approach (0.08% vs. 0.94%, P = 0.016), in a retrospective study including 1760 Chinese patients [46]. Our results were consistent with those from the aforementioned studies. The SSI rate here was 5.3% (34/647) and 0.9% (5/530) for open and laparoscopic approach, respectively. The lower SSI rate in laparoscopic approach may be explained by the short incision, the way for mesh introduced to the preperitoneal space (through the port) and the site where the mesh placed (not near the incision) [19]. However, the laparoscopic operation is not suitable for all the patients as it is preformed under general anesthesia and requires a higher surgical cost. It is, therefore, recommended a comprehensive assessment of the necessity of antibiotic prophylaxis by the surgeons prior to open surgery.
The present study was limited by several factors. A limitation is the retrospective property of the study. However, a retrospective approach allowed a large study population. We lacked data of several potential risk factors related to SSI due to our observational study design, such as intraoperative body temperature and the dosage of smoking. Additionally, although we focused on mesh repairs, the limited follow-up time resulted in no mesh infections identified in our study.