Prevalence and risk factors of surgical site infection in patients with trauma

Introduction

A surgical site infection (SSI) is defined by the Centers for Disease Control and Prevention (CDC) as an infection that occurs at or near the surgical incision within 30 days of an operative procedure or within 90 days if an implant is placed [1]. According to the CDC’s National Healthcare Safety Network (NHSN), SSI are classified into three categories: superficial incisional, which involves only the skin and subcutaneous tissue of the incision; deep incisional, affecting deeper soft tissues such as the fascia and muscle layers; and organ/space infections, which involve any part of the anatomy (organs or cavities) other than the incision that was opened or manipulated during the operation. Diagnostic criteria may include purulent drainage from the surgical site, a positive culture from aseptically obtained specimens, a deliberate incision opening by a surgeon in the presence of local signs of infection, or a clinical diagnosis of SSI made by a qualified physician. The Centers for Disease Control and Prevention standardized definitions enable consistent surveillance and reporting of postoperative infections across healthcare facilities [2]. An additional part of postoperative infection surveillance involves assessing the wound contamination level at the time of surgery. Wound class is determined during surgery by a qualified member of the surgical team, such as the surgeon or circulating nurse, using the classification system adopted by the facility. Surgical wounds are classified based on the contamination level during the procedure, following a standardized four-tier system defined by NHSN. Class I (Clean) wounds are uninfected operative wounds with no signs of inflammation, created during procedures that do not involve entry into the respiratory, alimentary, genital, or urinary tracts; if drainage is needed, a closed system may be used. Class II (Clean-Contaminated) wounds involve controlled entry into these tracts and carry a minimal but expected contamination level. Class III (Contaminated) wounds include those where a major breach in sterile technique has occurred, there is spillage from the gastrointestinal tract, or there is acute, non-purulent inflammation. Class IV (Dirty/Infected) wounds are characterized by pre-existing infection or gross contamination before incision, such as procedures involving debridement of devitalized tissue, abscesses, or perforated viscera. This classification provides essential context for evaluating surgical risk and interpreting postoperative infection outcomes. These classifications offer important information for assessing SSI risk and comparing surgical results across different institutions [3].
Although SSI are reported more frequently in economically less developed regions, where up to one-third of surgical patients are affected, they can occur in any healthcare setting performing surgeries [3]. According to CDC data, in 2024, SSI were observed in 1–3% of hospitalised surgical patients [1]. A 2023 systematic review and meta-analysis estimate a global SSI incidence of 2.5% [4]. Although the incidence is lower in high-income countries, SSI remain the second most common healthcare-associated infection in Europe and the USA. Surgical site infections prolong hospital stays, impose significant economic costs, and pose substantial risks to patient recovery as well as influence the patient’s quality of life. Therefore, preventing SSI is a global priority in surgical care [2].
The development of an SSI depends on multiple factors, especially bacterial exposure and the host’s ability to manage the inevitable bacterial contamination of the surgical incision. Surgical site infections are most often caused by bacteria introduced at the surgical site during the operation, with about 70–95% originating from the patient’s endogenous flora [5]. However, contamination from external sources – such as bacteria transmitted by surgical staff or heating and cooling devices – may also play a role. Risk factors related to SSI occurrence include advanced age, immunosuppression, obesity, diabetes, smoking, adequacy of antimicrobial prophylaxis, the condition of the surgical site tissues (e.g., presence of foreign material), the level of wound contamination, and factors related to the operation [6]. Especially in trauma wounds the main risk occurs in pre-hospital care and is related to the injury-related contamination.
The study is aimed to identify factors that influence the risk level according to the surgical site infection risk index (SSIRI) in patients with identified infection at the surgical site during the hospitalisation period.

Material and methods

Study design

The prospective observational study was conducted.

Participants

Patients over 18 years of age operated on for trauma at a clinic of accident surgery (in the second largest university hospital in our country) with early SSI occurrence.

Data collection design

The study was conducted at the second largest university hospitals in our country for eleven months (March 2024 – January 2025), in five departments of the clinic of accident surgery. Information on the incidence of patients with SSI (who had per secondary intention wound healing) was evaluated using the haemodialysis access-induced distal ischaemia (HAIDI) hospital program where the epidemiological hospital centre evaluates the data. The haemodialysis access-induced distal ischaemia technology provides an innovative solution for the automated monitoring of healthcare-associated infections in hospitals. The system uses artificial intelligence, particularly machine learning and natural language processing, enabling it to read and analyse both structured data from electronic health records and unstructured textual notes created by physicians and nurses. Haemodialysis access-induced distal ischaemia can identify up to five times more infections than traditional methods, while also decreasing the administrative workload related to data collection and analysis by up to 90%. The system’s outputs include automated reports, pathogen analysis, monitoring of emerging risks, and tracking of antimicrobial resistance, offering clinical teams timely and targeted insights [7].
Data collection for each patient was conducted in two stages. In the first stage, all data were retrieved from the hospital information system electronic documentation and entered into an Excel spreadsheet. In the second stage, we applied the online surgical site infection risk score (SSIRS) model, which enables immediate calculation of an individual patient’s SSI risk [8]. Compared with the National Nosocomial Infections Surveillance System Basic SSI Risk Index, the SSIRS demonstrates significantly superior discriminatory performance. This model provides a standardised estimate of the 30-day postoperative SSI risk based on a combination of patient-related factors and surgical characteristics, with the total SSIRS derived from the sum of individual weighted risk components. For this analysis, anthropometric variables such as height and weight were converted into inches and pounds in accordance with the model’s input requirements. The resulting risk estimate is expressed as a percentage and categorised into four groups: low risk (0–2%), moderate risk (2–10%), high risk (10–30%), and very high risk (> 30%) [9].

Data analysis

Statistical analysis was performed using the Statistical Package for the Social Sciences version 26.0 with Fisher’s exact test at a significance level of p < 0.05. Results
Out of the total 1118 patients (689; 61.6% men and 429; 38.4% women) undergoing surgery at the abovementioned institution – clinic of accident surgery in the monitored period (March 2024 – January 2025), the early SSI (type I) occurence was confirmed in 54 cases, representing 4.8% during the monitored period. These patients formed the research sample, which was further analysed (Table 1).
Most patients with SSI had a moderate or high risk of SSI, but no difference was found between genders, age, body mass index (BMI) score, or smoking status in the risk scores in our study sample (Table 2).
As the research team is aware that the urgent surgical procedures are associated with a higher risk of infectious complications according to the SSIRS we wanted to make a more detailed analysis to confirm that urgent surgery can significantly increase the risk of infection. Significance was found for clean/contaminated wounds, both to medium and high risk according to the SSIRS. However, no significant association was identified for other surgical factors such as the type of anaesthesia used, American Society of Anesthesiologists (ASA) classification, or the duration of surgery (Table 3). Discussion
The prevalence of SSI in the clinic of accident surgery during the study period (March 2024 – January 2025) was 4.8%, exceeding the commonly reported range of 0.5–3% (2.5%) [1, 4]. This may be due to higher wound pre-hospital contamination influenced by the injury-related factors and more accurate monitoring enabled by HAIDI technology. Similarly, the possible explanation is that the study has been done during the summer time when there is a higher prevalence of trauma especially in the nature environment and thus injuries are commonly contaminated in the pre-hospital period.
Based on the CDC/NHSN diagnostic criteria for SSI [1], the incidence of infection associated with hospitalisation was evaluated in 12 patients (1.07%) among all patients meeting the SSI definition (4.8%). In the remaining cases, SSI primarily occurred due to the acute nature and initial contamination and pollution of open traumatic injuries before hospitalisation. However, it must be noted that the results may be underestimated, as a 90-day surveillance period – recommended for selected procedure categories, particularly those involving implants or orthopaedic devices – was not available in our dataset.
This study aimed to identify factors influencing the risk of SSI related to the patients with a confirmed SSI. No significant differences between women and men were observed in individual SSRIS (p > 0.05). Zwicky et al. [10] investigated whether male gender has a stronger impact on SSI development in abdominal surgery. They discussed potential causes of gender-related differences, focusing on hormonal influences in women and impaired wound healing in men due to higher visceral fat. However, even after adjusting for all potential confounding factors, their study could not confirm that gender significantly affects SSI risk.
In our study sample, SSI were most frequently reported in patients aged 40–69 years, which may be related to the demographic structure of the trauma surgery population. There were no statistically significant differences in SSIRS between age groups, although research suggests that the risk of SSI increases with age (≥ 60 years) [11, 12]. This could be also influenced by the number of comorbidities.
Malnutrition and obesity are significant risk factors for SSI development [13]. Adequate nutrition is crucial for immune competence, collagen synthesis, granulation tissue formation, and normal angiogenesis. Protein and micronutrient deficiencies impair both cellular and humoral immunity, reducing the ability to control microbial invasion and increasing the risk of wound dehiscence and secondary infection [14, 15]. Conversely, excess adipose tissue is poorly vascularized, which can lead to tissue hypoxia and inadequate oxygen and nutrient delivery necessary for wound healing. Additionally, chronic low-grade inflammation and insulin resistance in obese patients further impair immune function and tissue repair [16]. Although our study did not confirm a relationship between SSIRI scores and BMI values (p > 0.05), the increased risk of SSI in patients with malnutrition or severe obesity should nonetheless be considered.
Smoking also acts as a modifiable risk factor for SSI. It causes tissue ischaemia, interferes with inflammatory processes, and raises the incidence of postoperative wound infections [17, 18]. Although no significant differences in SSI risk were observed between smokers and non-smokers with SSI in our sample (p > 0.05), the proportion of smokers with SSI was higher (33.4%) compared to the non-SSI group (24.6%).
Perioperative antibiotic prophylaxis is defined as the administration of systemic antibiotics before or during a surgical procedure. Studies consistently demonstrate that perioperative antibiotic prophylaxis is both safe and highly effective in preventing postoperative infections [19–21]. In our study, perioperative antibiotic prophylaxis was administered to all patients in accordance with guideline-based indications, including appropriate timing, selection of antibiotic agent, and duration, in alignment with perioperative antimicrobial stewardship principles. The universal application of antibiotic prophylaxis is consistent with international guidelines and represents a key preventive measure in surgical care [22].
The monitored surgery procedure factors included the urgency of the operation, wound condition, type of anaesthesia used, patient classification according to the ASA scale, and the total length of the operation. The study results show a significantly higher incidence of SSI in patients undergoing the urgent surgery compared to planned procedures in high-risk patients (p = 0.049). Significance was also observed between clean/contaminated wounds and moderate risk (p = 0.047) and high risk (p = 0.049). Unlike elective interventions, emergency operations often provide limited time for preoperative optimisation of the patient’s clinical condition, including compensation of patient status related to the comorbidities (e.g. diabetes, hypertension), nutritional status, or adequate skin preparation [23]. Additionally, emergency surgery is more often performed in the context of contaminated or dirty wounds, prolonged operative duration, and haemodynamic instability, all of which contribute to impaired tissue healing and a higher incidence of SSI [24]. Preventative strategies in trauma setting are therefore challenging, highlighting the importance of strict adherence to perioperative infection control protocols. We did not confirm any relations for other surgical determinants such as the type of anaesthesia used, ASA classification, or duration of surgery in our study sample, although predictors of SSI occurrence were identified. Patients with an ASA score of ≥ III are considered to have a significantly increased vulnerability to SSI due to severe systemic disease, impaired physiological reserve, and diminished immune competence [1]. Higher ASA categories are consistently reported as being linked to increased SSI rates across surgical specialties, reflecting both the burden of comorbidities and decreased ability to withstand surgical stress and infection [12, 23]. Prolonged surgery duration is a well-recognised risk factor for SSI [25]. Longer procedures increase tissue exposure to potential microbial contamination and are often associated with greater tissue trauma, impaired local perfusion, and delayed wound healing [1]. Furthermore, longer surgeries can induce systemic stress and transient immunosuppression, decreasing the body’s capacity to fight microbial invasion. The combined effect of these factors, often compounded by complex procedures or higher-risk patients, contributes to a greater incidence of SSI [26]. To be able to identify the risk in our hospital there would be a need for a longer monitoring period. For our current study we did not confirm this.

Limitations

This study has several limitations that should be considered when interpreting the results. First, the sample size was relatively small, although the study period and the total number of monitored patients was quite big (1118 patients) but only 54 patients were identified and had SSI confirmed, which may limit the statistical power to detect differences between subgroups and reduce the generalisability of the findings. Second, SSI occurrence was monitored only within 30 days after surgery, by standard surveillance protocols. We acknowledge the importance of applying surveillance timeframes consistently and in accordance with CDC/NHSN recommendations, which specify a 30-day follow-up for all procedures and a 90-day follow-up for selected categories, particularly those involving implants or orthopaedic devices. In our study, a uniform 30-day surveillance period was used because this was the only timeframe available in the dataset. We did not have access to extended postoperative information, as many patients were followed and managed in outpatient facilities near their place of residence, which represents an inherent limitation of the available data. We acknowledge that this approach may lead to under-ascertainment of SSI in procedure types for which a 90-day follow-up is recommended. While this timeframe captures the majority of infections, it does not include late-onset SSI, particularly in patients with implanted medical devices, where infection may occur up to one year postoperatively. Finally, the study was restricted to patients undergoing trauma surgery, which may not fully reflect risk profiles or outcomes in other surgical specialties.

Conclusions

The study confirmed the multifactorial nature of SSI development in trauma patients. Surgery-related factors were found to have a more pronounced influence on SSI occurrence, with urgent procedures and contaminated wounds being identified as key contributors to an increased risk. Although no significant associations were found for gender, age, ASA classification, or surgery duration in our sample, the findings emphasize the importance of comprehensive perioperative assessment and targeted preventative strategies. The optimisation of modifiable risk factors, strict adherence to infection control protocols, and the routine use of antibiotic prophylaxis remain essential measures to minimize SSI incidence and improve surgical outcomes. Based on our study, the long-term study is planned.

Disclosures

1. Institutional review board statement: The study was approved by the hospital’s management – institutional ethical review board (IRB). No special number for the institutional ethical review board (IRB) has been given. All data were fully anonymized to protect patient confidentiality.
2. Assistance with the article: The authors would like to thank the hospital’s management for allowing the study to be done in the second largest university hospital in our country.
3. Financial support and sponsorship: None.
4. Conflicts of interest: None.

References