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Risk of surgical site infection in hand trauma, and the impact of the SARS-CoV-2 pandemic: A cohort study

Background Despite the ubiquity of hand trauma, there remains insufficient published data to reliably inform these patients of surgical site infection (SSI) risk. We describe the risk of SSI in a single-centre cohort of patients with hand trauma, with an analysis of the impact of the coronavirus disease-2019 (COVID-19) pandemic. Methods Retrospective data collection of consecutive patients who underwent surgery for hand and wrist trauma in a single plastic surgery centre over two, three-month periods. Demographic, injury and operative details, alongside prophylactic antibiotic use, were recorded. Burn injuries and wounds infected at presentation were excluded. Presence of SSI at 30 days (90 days if a surgical implant was used) was assessed. Results Overall, 556 patients – ‘Pre-COVID-19’ (n = 310) and ‘During COVID-19’ (n = 246) – were included. Risk of SSI was 3.6% in the aggregated cohort. Female patients were more likely to develop an SSI, even when adjusted for their greater prevalence of bite aetiologies (adj OR 2.5; 95% CI, 1.00–6.37 and p < 0.05). The absolute risk of SSI in the ‘Pre-COVID-19’ group was 2.3% and 5.3% in the ‘During COVID-19’ group. The relative risk of developing an SSI in the ‘During COVID-19’ group was 2.34 (95% CI, 0.95–5.78 and p = 0.06). Baseline characteristics were equivalent between the two groups. Conclusion The risk of SSI in hand trauma is the same as the nationally estimated risk for all surgeries; 3–5%. Changes in presentation and practice associated with the first wave of the COVID-19 pandemic did not appear to alter the risk of SSI in patients undergoing surgery for hand trauma.


Introduction
European data suggests that hand trauma accounts for up to one-in-five of all Emergency Department attendances. 1,2,3 In the United Kingdom (UK) alone, around five million people per year injure their hand or wrist, accounting for over 250,000 operations per year. 1,4 As with all surgery, these procedures carry a risk of developing a surgical site infection (SSI). SSI is defined by the Centers for Disease Control (CDC) criteria as an infection associated with an operative procedure that occurs at, or near the surgical incision, within the 30 days following the procedure, or within 90 days if a prosthetic implant is used during surgery. 5,6 SSIs are the most common preventable complication following surgery and the most common nosocomial infection. 7,8 SSIs complicate approximately 3 to 20 percent of all surgical procedures with a national study from the UK finding an SSIs risk of 5 percent. 7,8 However, this figure may be an underestimate given that over 60 percent of SSIs become evident after discharge and may be treated in the community. 9 Many have purported a lower SSI risk in hand and wrist surgery, with the anatomical region's excellent blood supply being the explanation. 10,11,12 It has been stated that hand surgeons are 'privileged to operate in an anatomic region that is less vulnerable to infection than most sites of the body.' 10 However, this is not substantiated by reliable data. Of the small number of studies that directly assess SSI in hand and wrist trauma, the risk ranges from 3 to 10 percent, reflecting similar risk as for all operative procedures. 8,13,14,15 There remains insufficient published data to reliably inform hand trauma patients of SSI risk.
The COVID-19 pandemic, caused by the SARS-CoV-2 virus, was officially declared by the World Health Organisation on March 11, 2020. 16 Since then, changes in practice across all specialties, including altered referral pathways and changes to surgical management, have become necessary to mitigate infection whilst managing the continued influx of day-to-day trauma. 16,17,18 It stands to reason that these changes, whilst introduced with the objective to limit transmission of COVID-19, may also reduce the risk of other transmissible infections. Recent evidence has also suggested that the patterns of hand trauma presenting to hospital have changed during the COVID-19 pandemic, with an increase in injuries caused by saws and other household tools. 19 We describe the risk of SSI in a single-centre cohort of hand trauma patients, with an analysis of the impact of the COVID-19 pandemic.

Materials and Methods
An interrupted time series service evaluation was designed in accordance with the STROBE statement checklist. 20 In keeping with UK National Health Service (NHS) Research Authority guidance, ethical approval is not required for such studies. 21 The project was formally registered prospectively. All patients who underwent surgery for hand and wrist trauma in a single secondary plastic surgery unit between 1 st May 2019 and 31 st July 2019 (Pre-COVID-19) and 16 th March 2020 and 16 th June 2020 (During COVID-19) were identified from the hospital's operating theatre records and cross-referenced with the plastic surgery department's daily trauma theatre list records. Our time series comprised two cohorts, one from before the COVID-19 pandemic and one group from during the UK's 'first-wave', to evaluate the impact of the pandemic with the resultant changes to practice, patterns of injury and surgical management strategies.
We reviewed the medical notes of included patients and extracted pre-specified data. Consecutive patients within the two periods who had sustained traumatic injuries to the hand and wrist, irrespective of age (including paediatric patients), were included. Hand and wrist trauma was defined as any soft tissue or bony injury that is sustained distal to, and not including, the distal Operative details including, type of surgery, whether a prosthesis or implant was used, perioperative prophylactic antibiotic use and procedure setting (main theatres or in a minor-operating theatre) were captured.
Patients' hospital notes from our centre -including ward notes, follow-up letters, clinic letters, and emergency department attendances -were examined for evidence of the development of an SSI within 30 days (90 days if a surgical implant was used), according to CDC criteria. For these patients, specifics of the treatment for their SSI were extracted, including antibiotic use and re-operation.

Data analysis
Continuous variables were assessed for normality using Shapiro-Wilk Test; normality was rejected if p < 0.05. Baseline characteristics were described using means ±standard deviation (SD) for continuous normally distributed variables, median and interquartile range (IQR) for continuous variables that were not normally distributed and rounded frequencies (percent) for categorical variables. P values were calculated using an unpaired t test for continuous data with Gaussian distribution and using Mann-Whitney U test for non-normal variables. Chi-square test was used to evaluate associations between categorical variables, with Fisher's exact test used when cell values were below five. Statistical significance was defined as a p < 0.05. When analysing patients with bilateral injuries, the patient was defined as the unit of analysis. 22 All analyses were performed in R (v4.0.3).
We anticipated that there would be a low event rate of SSI, based on current literature, and therefore did not plan to perform any more complex statistical analyses. During data analysis we encountered an association between sex and SSI risk, which was potentially confounded by bite injury. We therefore proceeded with an a posteriori logistic regression analysis to handle this confounding. Bite pattern was prioritised based on clinical reasons, before any multivariable analysis was undertaken.

Results
Overall, 556 patients (n = 310 in the 'Pre-COVID-19' group, and n = 246 in the 'During COVID-19' group) underwent surgery for hand and wrist trauma during this time-period and were included in this study. Twenty patients developed an SSI, giving an overall risk of 3.6 percent in the aggregated cohort. All of these patients received antibiotics for the SSI and 12 returned to theatre for further surgery. The baseline characteristics for all 556 patients are shown in Table 1.
The majority of cases (n = 406; 73 percent) of hand and wrist trauma were sustained by men and the median age was 39. Three-hundred and thirty-seven (61 percent) procedures were carried out in a minor-operating theatre. Most were 'sharp' injuries (n = 238, 45 percent), followed by 'rip, tear or crush' injuries (n = 219, 39 percent). Animal bites accounted for 69 (12 percent) of the injuries.
Another 100 (18 percent The 'Pre-COVID-19' group and the 'During COVID-19' group had similar pre-operative baseline characteristics in terms of age, sex and mechanism of injury, as can be seen in Table 3.

Discussion
The overall risk of SSI in our cohorts was in line with the national UK estimate of 3-5 percent for all surgical procedures. 8 The pandemic led to a shift towards minor-operating theatre and local anaesthetic procedures, which did not appear to be associated with an increased risk of SSI.
Our results are comparable with the findings of a recent multi-centre cohort study examining upper extremity surgery, for any indication, during the COVID-19 pandemic, which, as a secondary outcome, found the risk of SSI to be 3 percent. 23 These results contrast the findings of an observational study from Italy that reported rates of SSI to be reduced in general surgery patients during the COVID-19 pandemic. 17 This was accredited to vigilant wearing of face masks and closing the ward to visitors. 17 Our hospital introduced similar measures. Other changes introduced to reduce patient contact at our centre, specific to hand trauma, included greater use of absorbable skin sutures and a telemedicine follow-up system.
The effect of the pandemic on the clinical pathway of patients with SSI is unclear. It is possible patients with hand and wrist SSI may have chosen to avoid hospitals due to the risk of contracting COVID-19, preferentially seeking treatment in primary care settings. In contrast, with the concomitant reduction of primary care availability during the pandemic, it is also feasible that more SSI patients will have attended the emergency department for treatment. The latter cohort of patients will have been identified in our cohort, whereas the former will not. This could lead to either apparent underestimation or overestimation of SSI risk that is specific to hand and wrist patients during the pandemic. Further evaluation of national primary care datasets would help to ascertain the number of patients that are treated for hand SSI, giving a more accurate representation of overall risk.
Fewer patients received surgery for hand and wrist trauma in our centre during the first wave of the COVID-19 pandemic. Patient characteristics were comparable to those presenting prior to the pandemic, other than fewer patients smoking, which may be explained by data suggesting that smoking cessation attempts have increased in the UK during the pandemic. 24 This similarity between the two groups indicates that a comparable patient population with equivalent types of injuries are presenting with hand and wrist trauma during the COVID-19 pandemic, despite national lockdown and changes to peoples' working and social lives. These findings are reflected in other studies examining hand trauma during the COVID-19 pandemic. 19,25 Discourse looking at the specific activity implicated have suggested that sports related trauma was reduced whilst domestic 'do-it-yourself' (DIY) injuries and injuries related to deliberate self-harm (DSH) were more prevalent. 19,25,26 In our cohort, a greater proportion of females developed SSIs than males, even when adjusted for their greater prevalence of bite aetiologies. Previous literature has demonstrated that SSIs generally occur more frequently in male patients than in female patients. Females have been found to be less likely than males to develop SSIs when undergoing hip, knee and intra-abdominal procedures, but more likely to develop SSIs when undergoing coronary artery bypass grafting and hernia repairs. 27 Some investigators have argued that these findings may be explained by differences in fat distribution between male and female patients or even due to differences in bacterial skin colonisation between sexes. 27 Differences in attitude toward seeking medical attention may present another confounding factor contributing to this finding. Men are purportedly less likely to consult their doctor, which could lead to reduced rates of detection of SSI in male patients. 28 Previous discourse examining SSI risk has reported varying degrees of importance of pre-and perioperative factors, such as wound contamination, grade of vascular disruption, smoking status, presence of systemic illness, use of prophylactic antibiotics and location of procedure, but their findings are often contradictory. 11,12,14,29 Our study did not reveal any variation in risk of SSI with different mechanisms of injury, level of contamination, ASA grade or smoking status.
The majority of our patients received perioperative prophylactic antibiotics, including those who later developed an SSI. Prophylactic antibiotics in hand surgery is a contentious issue. 30,31,32,33 Antibiotic stewardship requires evidence-based rationale for the safe and effective use of antimicrobials. For simple hand injuries that require surgery, the findings of a recent meta-analysis of 2,578 patients suggested that prophylactic antibiotics did not significantly reduce subsequent infection. 30 The indications for hand and wrist procedures that can be performed as day case procedures under local or regional anaesthetic outside of the main operating room is continually growing. 29,34,35 There have been reported worries that these areas may not function with the same stringent level of infection control as the main operating theatre, however the results of our study, alongside those previously published, have not confirmed this belief. 29,36 We found that there was increased use of the department's minor-operating theatre during the first wave of the pandemic. This is in keeping with guidance published by the British Society for Surgery of the Hand (BSSH) and comparable to other centres in the UK. 18,23 The move away from the main operating theatre may also explain the reduction in patients receiving prophylactic antibiotics.

Limitations
This study only captured patients who developed SSIs and presented back to our secondary plastic surgery unit. This study will not have captured any patients who developed an SSI and were managed in primary care or by another hospital, if they were not then referred back to our department. Most patients were discharged the same day and, as such, the majority of the 30-day (or 90-day) period in which an SSI may occur was spent away from the hospital with no, or minimal, contact with medical professionals. Given that 60 percent of SSIs become evident after discharge, this means that there is a possibility that this study will have missed SSIs. 9 This is especially true for hand trauma, where the vast majority of patients are ambulatory. Future studies investigating this area could be improved by being prospective, with specific patient follow-up to find out if patients develop SSIs and are treated in the community. Severity of SSI, other than the need to return to theatre, and the consequences of the SSI were not assessed by this study. As logistic regression was not originally anticipated, we did not perform an a priori sample size calculation to determine power. Due to the potential underpowering of this study, further posteriori multivariate models could not be explored because of the risk of providing spurious significant results and leading to data that was not robust.

Conclusion
The risk of SSI in hand and wrist trauma in this cohort is the same as the nationally estimated risk for all surgery; 3 to 5 percent. 8 Changes in presentation and practice associated with the first wave of the COVID-19 pandemic did not appear to alter the risk of SSI in patients undergoing surgery for hand and wrist trauma. Our study found that female patients were more likely to develop an SSI, even when adjusted for their greater proportion of bite injuries. It is unclear from this study whether sex represents a true risk factor for the development of SSI in hand and wrist trauma. However, given previous data showing that sex is an independent risk factor for SSI in other anatomical areas, this should not be ruled out. National-level data analysis may provide a deeper understanding of baseline SSI risk in hand and wrist trauma, along with potential for risk factor exploration and risk stratification.

Ethical Approval
None required.  2) Wood, soil, metal and glass foreign bodies 3) Including debridement, washout, repair of laceration and removal of foreign body 4) Other procedures included evacuation of haematoma, replant, skin graft, thenar flap recon § p-value derived using Mann-Whitney U test for non-parametric data. † p-value derived using Chi-square test for categorical variables. ‡ p-value derived using Fisher's exact test when cell sizes were below five.

Tables
Significant p-values are highlighted.