Assessment of risk factors associated with surgical site infection following abdominal surgery: a systematic review

Introduction

Surgical site infection (SSI) is defined by the Centers for Disease Control and Prevention (CDC) as the infection occurs within 30 days of the surgical operation at the site of the surgery, or within a year if an implant is left in place, and the infection is thought to be secondary to surgery.1 SSIs are classified by the CDC into three categories: superficial incisional if limited to the skin and subcutaneous tissue at the site of the incision, deep incisional when involving fascial and muscle layers, and organ space when involving a body cavity or visceral organs.1 2

These SSIs are among the most common healthcare associated infections, occurring following 1%–3% of all surgical procedures,3 and their rates are much higher following abdominal surgeries than with other types of surgeries, with many studies indicating wide variations in the reported incidences based on the operating conditions.3–6

Although regulations of antisepsis were described very early by Joseph Lister in 1867, SSI is still a common problem in surgical patients despite of the advancements in the medical field.2 It is associated with increased morbidity, readmissions, length of hospital stay, mortality, and healthcare costs.7–10

With the rising rates and morbidities associated with these infections, various studies have made several efforts to find better ways to optimize patients prior to surgery or improve perioperative conditions and management of patients during the recovery period in order to prevent SSIs,11 12 including the recommendations published by the WHO.13

The risk factors associated with the development of an SSI vary according to specific patient factors and clinical characteristics, in addition to the nature of the surgical procedure.14 Despite the considerable number of clinical studies that have reported on these risk factors for SSIs following abdominal surgeries, it can be challenging to control the level of details available and to comprehensively adjust for all the variables in the estimation of particular risk factors.15 A comprehensive and detailed assessment of the multifactorial nature of these risk factors could help in improving the quality of surgical care.

To our knowledge, there are no previous systematic reviews in the literature that studied the risk factors of SSIs following the different types of general abdominal surgeries in particular. Moreover, as a high level of evidence is greatly needed in the surgical literature, this systematic review comes to comprehensively identify and assess the current evidence of these predictive factors of postoperative wound infections after abdominal surgery as they have been published in the medical peer-reviewed literature, taking into consideration the potential confounders. We believe that the results of our study will add recent evidence that will help in improving surgical management by forming evidence-based strategies to decrease the rates of preventable SSIs by targeting their potential risk factors; one can improve patient safety.10

Methods

Search strategy and study selection

A vigorous, maximum sensitive and online search of the literature was performed. The search strategy was limited to published articles in the last 20 years (January 2002–December 2021) to include the most recent, up-to-date data that reflect the current clinical practice. The databases searched were MEDLINE (via PubMed) and Cochrane Library. The search terms used were “risk factors”, “surgical site infection”, “surgical wound infection”, “abdominal surgical infection”, and “abdominal surgery” combined with “AND” and “OR” operators as appropriate. The reference lists of the included studies were also searched manually to exhaustively retrieve additional relevant articles.

The review and selection of studies were performed based on specific inclusion and exclusion criteria in two screening stages. The first stage of screening was performed based on the titles and abstracts. Eligible studies were screened based on the full text in the second stage. Figure 1 shows the flow of the selection process. The search strategy and study selection were performed by two independent reviewers; any discrepancies were resolved by discussion and consensus.

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Figure 1

Flow diagram outlining the review process and study selection.

Results

Discussion

Despite the widespread adoption of advanced preventive strategies, surgical wound infections continue to occur. Recent evidence in the surgical literature is a base for recommendations and additional options to further reduce the incidence of wound infection. This comprehensive systematic review identified 11 eligible articles that studied risk factors for SSI following abdominal surgery. Nine studies were assessed to be of high quality, and the remaining two studies were of moderate quality.24 30 No restrictions were placed on the geographical region where the study was conducted, but all included studies were conducted with regard to the regular perioperative care. All the included studies were observational cohort studies. This allowed us to report a comprehensive review because observational studies allow a wider breadth of reporting of risk factors for SSI in abdominal surgery; this can be achieved in the routine clinical practice for a larger range of patients, unlike the narrow focus on specific risk factors.

The rates of SSI ranged from 4.09% to 26.7%. These rates in abdominal surgery are higher than other types of surgeries, as compared with similar systematic reviews in spinal surgery,33 dermatological surgery,34 and orthopaedic surgery.35

A number of significant risk factors were identified in the included studies; these include demographic, perioperative, and procedure-related factors. Age was assessed by all studies; only one moderate-quality study identified advanced age as a risk factor for SSI in the univariate model. This is consistent with other reports that associate SSI with people older than 60 years36; however, this result should be interpreted with caution as it is unlikely that older age has a direct and independent relationship due to the number of confounding factors associated with the ageing process that might lead to poorer wound healing. Two studies identified male gender as an independent risk factor22 26; this relationship has been identified in many specific studies,37 and can be supported by the fact that in men, androgens have a proinflammatory effect on wounds, which impairs re-epithelialization process, whereas in women, estrogens have been shown to have an anti-inflammatory effect, which could account for the difference.38 Moreover, the health behaviours and practices of men regarding wound care might contribute to the difference. As expected, well known and reported comorbidities that affect the development of SSI such as increased BMI and diabetes were identified as significant risk factors in our review.39 One study23 defined overweight as a risk factor in the univariate model, and another two studies25 26 defined BMI of >25 as an independent risk factor. This is consistent with the fact that adipose tissue has poor vascularization; as a result, it creates a suitable environment for proliferation of micro-organisms. However, BMI does not accurately reflect the body’s fat composition; we suggest using of parameters such as visceral fat area, subcutaneous fat thickness, and abdomen depth for more reliable SSI prediction in abdominal surgery.40 41 Diabetes was demonstrated as a significant risk factor in two studies23 26; the immunological and vascular complications of diabetes might be associated with wound infection.42

Smoking is generally believed to contribute to infections due to various effects on capillary oxygen transfer, tissue perfusion, and coagulation.43 It is identified as an independent risk factor in one high quality study.26

ASA classification system is a known indicator that reflects combined co-morbidities and physical conditions, the scoring system ranges from (I) for an otherwise healthy patient to (V) for those patients not expected to survive the next 24 hours.44 Three studies in this review found that ASA classification 3 and 4 is a significant risk factor for development of SSI,26 28 29 possibly the higher the classification, the higher risk.

Low albumin level was identified as an independent risk factor in one high quality study.26 In hypoalbuminemia there is no adequate preoperative nutritional support which is essential to optimize surgical outcomes, this result in wound infection.45 Similarly, low hemoglobin concentration associated with an increased risk of wound infection due to tissue hypoxia as reported in past studies,12 this was confirmed in our review as one high quality study defined hemoglobin level <12 g/dL as an independent risk factor.25 One high quality study demonstrated that patients undergoing chemotherapy are at risk of developing SSI in the univariate model23; however, we suggest that further specific studies will help in describing these risks for developing an SSI. Two high quality studies28 29 and one moderate quality study30 identified the length of pre-operative hospital stay as a risk factor using various definitions; colonization of infectious micro-organisms during the prolonged preoperative hospital stay may be the responsible cause for the increased infection risk.

Two studies assessed the significance of the number of people in the operative theater as risk factors23 26; one of them reported a statistical significance of more than 10 people in the univariate model23; however, it is difficult to comprehensively conclude, and these results should be interpreted with caution, so we recommend further specific studies for conclusive outcomes. Not surprisingly, eight studies identified operative time as a significant risk factor using various definitions.22 23 25–30 In fact, this relationship is complex and can be explained by the prolonged exposure to environmental factors, complexity of the case, and occurrence of intraoperative complications, which have been reported in other specific studies.46 Emergency abdominal surgery was reported to have a significant greater risk of postoperative wound infection than elective surgery in five studies22 26 28 30 32; it is regarded as one of the non-modifiable risk factors that could result from lack of readiness for operative procedures. One high-quality study determined open surgical approach as an independent risk factor22; this is consistent with specific reports in abdominal surgery, which conclude that open surgical approach results in larger incision which act as a breeding place for infectious agents.47–49 Dirty-infected wound class was reported as a significant risk factor in eight studies23 24 26–30 32 as compared with other wound classes; this relationship is significantly direct, the wound class; the higher risk of infection (dirty, contaminated, clean-contaminated, or clean), this is not surprising, as the probability of developing SSI is greater due to increased bacterial load. Intraoperative blood loss is another significant independent risk factor which was identified in two studies24 32; as a consequence, it will increase the need for blood transfusion, which is also a risk for SSI. Perioperative infection and high intraoperative temperature nadir were demonstrated as independent risk factors in one study.31 Presence of current infection could complicate surgical outcomes; we suggest that the enhanced perioperative care in patients with concomitant infections would highly decrease the burden of SSIs. To further evaluate intraoperative temperature as a risk factor, we considered a number of specific trials; it was surprising that some reports demonstrated that avoidance of intraoperative hypothermia reduces the incidence of postoperative wound infection50; moreover; our included study reported that despite the statistical significance, difference in temperatures between the both groups is so narrow and clinically negligible, so we recommend further specific assessments regarding this risk factor for SSI. Various reports demonstrated the use of allogeneic blood as a strong factor that increases the risk of infection in patients following surgery.51 Similarly, perioperative blood transfusion is reported as an independent risk factor in three studies24 28 31 due to the known immunosuppressive impact of intraoperative blood transfusion that might give rise to the risk of wound infection. The use of drains postoperatively was identified as a significant risk factor in three studies using various definitions27–29; this is due to colonization and micro-organisms.

It is important to mention that many modifiable risk factors in abdominal surgery such as wound care, operating room environment, preoperative hair removal, and bowel preparation are common risk factors for SSI; we believe that the preoperative prevention interventions for these factors are carried out routinely in the surgical institutions.

Conclusions

This comprehensive systematic review indicated that male sex, increased BMI, diabetes, smoking, ASA classification of >2, low albumin level, low hemoglobin level, preoperative hospital stay, long operative time, emergency procedure, open surgical approach, increased wound class, intraoperative blood loss, perioperative infection, perioperative blood transfusion, and use of drains are potential independent risk factors for SSI following abdominal surgery. The study also concluded that there is a need for an institutional definition when reporting SSIs; it can be used during prospective, comparative, or even randomized studies targeting the risk factors they have identified.