Local vancomycin powder reduces surgical site infections and costs in spine surgery: a retrospective cohort study in a public hospital in Santiago, Chile

Introduction

In spine surgery, surgical site infections (SSIs) continue to pose a major challenge, leading to increased patient morbidity, extended hospitalization periods, and significant financial burdens on healthcare systems (1). These infections remain a notable postoperative complication, impacting both patient outcomes and healthcare resources. The incidence of SSIs varies widely across studies, ranging from 0.2% to over 16%, depending on factors such as surgical approach, instrumentation, and patient population (1-3). A recent meta-analysis by Zhou et al. [2020] (1) reported a pooled SSI incidence of 3.1% across 27 studies involving 22,475 patients, with a lower SSI rate observed in cases where local vancomycin powder was applied (1.9%) compared to its absence (4.8%) (1). These findings suggest that vancomycin powder may be an effective prophylactic measure for reducing SSIs in spine surgery (4).

Despite promising results, the efficacy of vancomycin powder remains a subject of debate, particularly in specific patient populations. While several studies have demonstrated its effectiveness in adult populations (4,5), its utility in pediatric patients, such as those with adolescent idiopathic scoliosis (AIS), is less clear. For instance, Zhang et al. [2024] (6) observed no significant difference in SSI rates between the vancomycin and control groups in a large multicenter cohort of AIS patients undergoing posterior spinal fusion (0.5% vs. 0.8%, P=0.451) (6). These conflicting findings underscore the need for further research to clarify the role of vancomycin powder in various surgical contexts and patient populations (2,4,7,8). Additionally, while the clinical benefits of vancomycin powder have been explored, its economic impact—particularly in resource-constrained healthcare systems—remains understudied.

Given the variability in existing evidence and the lack of comprehensive cost analyses, this retrospective cohort study aims to evaluate the impact of local vancomycin powder on SSI rates and associated costs in a single-institution cohort of patients undergoing spine surgery. This study seeks to provide actionable insights into the clinical and economic benefits of vancomycin prophylaxis in spine surgery by addressing these gaps. We present this article in accordance with the STROBE reporting checklist (available at https://jss.amegroups.com/article/view/10.21037/jss-25-38/rc).

Methods

This retrospective cohort study examined data from patients who underwent instrumented spinal surgery at Hospital Barros Luco Trudeau between January 2017 and December 2019. A total of 205 patients met the inclusion criteria and were included in the analysis.

Eligible participants were at least 18 years old and had undergone open posterior spinal fusion at any level from the craniocervical to the lumbosacral junction. The study excluded cases involving minimally invasive techniques and those with less than 6 months of post-operative follow-up. Participants were divided into two groups based on vancomycin powder usage: a control group (n=84) that did not receive the powder, and a vancomycin group (n=121) that received suprafascial vancomycin powder during the operation. Data were extracted from the hospital’s electronic medical records (EMRs) and included Demographic data included age, body mass index (BMI), and comorbidities. Surgical data included the surgical approach, the number of levels fused, the presence of interbody fusion, operative time (in minutes), the type of pathology, and details of relevant comorbidities. Postoperative data included the occurrence of SSI, defined as an infection occurring at or near a surgical incision within 30 days after the procedure—or within 90 days to 1 year if an implant was placed—and affecting the incision or deeper tissues/organs that were manipulated during the surgery (9) and associated hospitalization costs, antibiotic costs, and estimated costs of reoperations.

Definition of SSI

The definition of SSIs was based on the guidelines provided by the Centers for Disease Control and Prevention (CDC)/National Healthcare Safety Network (NHSN) (10,11). The classification of SSIs was established as follows:

Superficial infection: develops within 30 days post-surgery, affecting only the skin and subcutaneous layers. It is characterized by at least one of the following: pus discharge, positive culture from aseptic sampling, surgical opening of the wound, or surgeon’s diagnosis (2).

Deep infection: manifests within 30 or 90 days after surgery, depending on the procedure type (30 days for laminectomy, 90 days for fusion). It involves the fascia and muscle layers and is identified by pus drainage from deep tissues, surgical opening with confirmed presence of microorganisms, abscess formation, or other histological indicators of infection (2).

Organ space infection: occurs beneath the muscle and fascia layers, sharing the same diagnostic criteria as deep infection (12).

The study size was determined by the number of patients who underwent instrumented spinal surgery at Hospital Barros Luco Trudeau between January 2017 and December 2019 and met the inclusion criteria. Statistical analyses were performed to compare outcomes between the control and vancomycin groups. Continuous variables, such as age and operative time, were compared using independent t-tests or Mann-Whitney U tests, as appropriate. Categorical variables, such as SSI rates, were compared using Chi-squared tests or Fisher’s exact tests. A P value <0.05 was considered statistically significant. All analyses were conducted using IBM SPSS Statistics, version 30.0 (IBM Corp., Armonk, NY, USA).

Potential confounders such as age, BMI, and comorbidities were controlled for in the statistical analysis to minimize bias and missing data were handled by excluding cases with incomplete information from the analysis.

All patients provided written consent authorizing the authors to review their clinical data and use the information in future scientific publications, with the assurance that all data would remain anonymized.

Statistical analysis

Statistical analyses were performed using IBM SPSS Statistics, version 30.0 (IBM Corp., Armonk, NY, USA). Continuous variables were assessed for normality using the Shapiro-Wilk test. Data with normal distribution are presented as mean ± standard deviation and were compared using independent t-tests. Non-normally distributed data are presented as median (interquartile range) and were compared using the Mann-Whitney U test. Categorical variables are presented as counts and percentages and were compared using the Chi-squared test or Fisher’s exact test, as appropriate. A P value of <0.05 was considered statistically significant for all tests. The number needed to treat (NNT) was calculated as the reciprocal of the absolute risk reduction.

Ethical considerations

The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Ethics approval was waived by the institutional review board of Hospital Barros Luco Trudeau in this retrospective study that uses exclusively anonymized data extracted from medical records for quality improvement and audit purposes.

Vancomycin application protocol

Patients in the vancomycin group (n=121) received 1 g of sterile vancomycin powder applied suprafascially during wound closure. The powder was distributed uniformly over the fascial plane and surgical bed after final irrigation and before fascial closure, consistent with standard dosing protocols (4,13).

Selection criteria for vancomycin use

The decision to use vancomycin powder was based on surgeon’s discretion considering: surgical complexity (≥3 levels fused, revision surgeries), patient risk factors (diabetes mellitus, BMI >30 kg/m², immunocompromised status), high-risk procedures (trauma cases, prolonged operative time >3 hours). No institutional protocol mandated its use during the study period.

Results

This retrospective cohort study included 205 patients who underwent instrumented spinal surgery at Hospital Barros Luco Trudeau between January 2017 and December 2019. Patients were divided into two groups: a control group (n=84) that did not receive vancomycin powder and a vancomycin group (n=121) that received suprafascial vancomycin powder during the surgical procedure (Figure 1 and Table 1).

Figure 1 Flow diagram of patient distribution.

SSI incidence contextualization

Among the patients included in the study, all of whom received the same prophylactic treatment, 76.9% developed SSIs, while 23.1% did not. To calculate these proportions, the two datasets—groups with SSI and groups without SSI—were merged into a single cohort. A binary indicator variable was created to distinguish between patients with and without SSI, allowing for straightforward tabulation of infection status.

Given that the entire population under study received the same treatment regimen, the analysis was limited to descriptive statistics. The proportion of patients with SSI was calculated using frequency and relative frequency tables. The resulting infection rate reflects the burden of SSI among treated individuals, but no statistical inference was conducted due to the absence of a comparator group and the limited sample size.

These findings highlight that a substantial proportion of patients developed postoperative infections despite having received prophylactic treatment, suggesting the need for further investigation into contributing clinical or procedural risk factors. However, due to the small sample and lack of untreated controls, no conclusions can be drawn regarding treatment effectiveness or causality.

Microbiological susceptibility

All Gram-positive isolates (Staphylococcus aureus) demonstrated susceptibility to vancomycin. Gram-negative pathogens (Klebsiella pneumoniae, Escherichia coli) showed intrinsic vancomycin resistance but were sensitive to alternative agents (Table 2).

Cost analysis

The average antibiotic cost was USA dollar (USD) 328 in the control group and USD 356 in the vancomycin group (P>0.05, independent samples t-test). However, the average hospitalization cost was significantly lower in the vancomycin group (USD 1,314) compared to the control group (USD 1,481; P<0.05, independent samples t-test). The total cost per 100 patients was substantially lower in the vancomycin group (USD 4,139) compared to the control group (USD 21,506; P<0.05, Mann-Whitney U test). Additionally, the average hospital stay for patients who developed an SSI was significantly shorter in the vancomycin group, with a mean reduction of 6.4 days (P<0.05, independent samples t-test). Vancomycin prophylaxis resulted in an average cost savings of USD 17,368 per 100 patients operated, highlighting its potential economic benefits alongside its clinical efficacy in reducing SSIs (Table 3).

The overall SSI rate was 6.3% (13 out of 205 patients). The SSI rate was significantly higher in the control group (11.9%, n=10) compared to the vancomycin group (2.48%, n=3; P<0.05, Chi-squared test). Comparative quarterly data showed a clear trend in favor of the vancomycin group, with differences between the two groups of up to 25 percentage points over similar time periods, as shown in Figure 2.

Figure 2 Comparative quarterly infection rates in treated and untreated groups. The graph shows the infection rates (%) for the vancomycin-treated group and the control group over four quarters. The vancomycin group consistently demonstrated lower infection rates compared to the control group. There were no missing data for the primary outcome (SSI rates), the absolute risk reduction was 9.42%, and the number needed to treat was 11. SSI, surgical site infection.

Discussion

This retrospective cohort analysis underscores the potential benefits of using local vancomycin powder as a preventive measure in spine operations. The study reveals a 70% decrease in SSI rates, resulting in substantial cost reductions for healthcare providers. These outcomes align with previous research demonstrating the efficacy of intrawound vancomycin powder in reducing infection rates across various surgical procedures, including spinal and craniotomy operations (8,13). Applying topical vancomycin powder provides a concentrated antibiotic dose directly to the surgical site, decreasing the likelihood of wound separation and infection (14). Furthermore, its localized use limits systemic absorption while offering sufficient prophylactic protection against gram-positive bacteria (15).

Utilizing vancomycin powder lowers SSI rates and diminishes the occurrence of vancomycin-associated side effects. Kidney toxicity, the most commonly reported adverse reaction linked to intravenous vancomycin administration, affects up to 20% of patients following standard dosages (15). Other less frequent adverse effects include osteoblast toxicity, low blood pressure, and hearing impairment. However, concerns about osteoblast toxicity have been raised, with Guimbard-Pérez et al. (16) reporting a 32% reduction in fusion rates in a rabbit spine model following the administration of a dose five times the standard. Despite these concerns, the benefits of vancomycin powder in reducing SSIs and associated costs are substantial, making it a valuable prophylactic measure in spine surgery.

The 11.9% SSI rate in controls exceeds rates in comparable studies [3.1–4.8% (3)]. This likely reflects our institution’s high-risk caseload (60% trauma cases among infected controls), resource constraints, and exclusive focus on open instrumented procedures. These findings underscore the need for bundled interventions beyond antibiotic prophylaxis.

Concerns about microbial resistance warrant careful consideration. While significant evidence supporting the development of resistance is lacking, some studies suggest that topical antimicrobial prophylaxis may exert “selective pressures on wound flora” (17). The Infectious Diseases Society of America recommends maintaining vancomycin levels above 10 µg/mL to mitigate the development of resistance (18). However, the subtherapeutic systemic absorption associated with localized vancomycin application may result in drug concentrations insufficient to inhibit bacterial growth, potentially leading to the proliferation of resistant strains, such as Staphylococcus aureus (19). All gram-positive isolates were vancomycin-susceptible, explaining the absence of gram-positive SSIs in treated patients. Gram-negative pathogens (intrinsically vancomycin-resistant) caused 50% of control-group SSIs, suggesting need for complementary prevention strategies.

In addition to its antimicrobial properties, vancomycin powder has gained popularity for its cost-effectiveness (13,18). Using vancomycin powder not only helps prevent infections but may also reduce the need for additional surgeries and associated healthcare costs. In this study, vancomycin prophylaxis resulted in an average cost savings of USD 17,368 per 100 patients operated, primarily due to reduced hospitalization costs, shorter hospital stays, and fewer reoperations. These significant cost savings further support its use as a cost-effective prophylactic measure, particularly in resource-constrained healthcare systems.

While the use of vancomycin powder as a preventive measure offers advantages, it requires thorough evaluation before implementation. This study’s retrospective approach presents a constraint, potentially introducing biases and confounding variables. Subsequent research should encompass larger patient groups and employ prospective, randomized controlled trials to confirm these results and develop standardized protocols for topical antibiotic use in spinal procedures. Moreover, investigating the effectiveness of various types and concentrations of topical antibiotics could yield additional insights into enhancing prophylactic methods for SSI prevention.

This study has several limitations. It estimates the occurrence of SSIs in a cohort of all patients receiving the same prophylactic treatment, comprising two groups: those with SSIs and those without. A binary variable indicated infection status, and both groups were combined for analysis. Descriptive statistics summarized the infection rate, but no inferential tests were performed due to the absence of a control group and uniform treatment. The sample size and lack of variation in treatment precluded the use of more complex models, such as logistic regression or hypothesis testing, as these methods would violate their assumptions and potentially yield unreliable results.

Conclusions

Local vancomycin powder (1 g applied suprafascially) significantly reduced SSIs in high-risk spine surgery, particularly against gram-positive pathogens to which all isolates were susceptible. The elevated baseline SSI rate in our trauma-dominated cohort highlights the value of this intervention in resource-constrained settings, yielding substantial cost savings ($17,368/100 patients) driven by decreased antibiotic usage, shorter hospital stays, and fewer repeat surgeries.

These findings have important implications for the management of spine surgery patients, particularly in resource-constrained settings. By reducing both infection rates and associated healthcare costs, vancomycin powder represents a cost-effective prophylactic measure that can optimize resource utilization and improve patient outcomes. However, the retrospective nature of this study highlights the need for further research, including prospective, randomized controlled trials, to validate these results and establish standardized guidelines for topical antibiotics in spine surgery.

In conclusion, using local vancomycin powder in spinal surgery offers a promising approach to reducing SSIs and associated healthcare costs. Future studies should explore long-term outcomes, including the potential for antibiotic resistance, to ensure the sustained efficacy and safety of this intervention.

Acknowledgments

None.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jss.amegroups.com/article/view/10.21037/jss-25-38/rc

Data Sharing Statement: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-38/dss

Peer Review File: Available at https://jss.amegroups.com/article/view/10.21037/jss-25-38/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jss.amegroups.com/article/view/10.21037/jss-25-38/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. Ethics approval was waived by the institutional review board of Hospital Barros Luco Trudeau in this retrospective study that uses exclusively anonymized data extracted from medical records for quality improvement and audit purposes. All patients provided written consent authorizing the authors to review their clinical data and use the information in future scientific publications, with the assurance that all data would remain anonymized.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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