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Healthcare-associated infections (HAI) are a major source of morbidity, mortality and expense. Surgical site infections (SSI) make up approximately 22% of HAIs in the US1 and 17% in Europe.2 SSIs increase hospital inpatient length of stay (LOS) by a median of two weeks, increase the chance of readmission and re-operation by five times, and double mortality.3

Surgical site infections can be divided into superficial and deep incisional/organ space (henceforth referred to as ‘deep’) as per the Centre for Disease Control and Prevention (CDC) . Superficial infections usually respond well to antibiotics and wound cares. Deep infections involve deep soft tissue or organs/spaces opened or manipulated during the operation and must occur within 30 days of the procedure or within one year if an implant is in situ.4 Deep infections cause the most severe morbidity and are usually managed with surgical debridement, by sending intra-operative tissue samples for microbiology, and intravenous (IV) followed by oral antibiotics targeted at likely or confirmed pathogens.

Surgical site infections are a significant risk of spinal surgery. A recent literature review looking at 425,180 primary spinal procedures calculated a pooled average SSI rate of 1.9%.5 Approximately half of these appear to be deep infections. Lieber et al reviewed the National Surgical Quality Improvement Program Database (NSQID) in the US between 2006 and 2012 and identified 1,110 post-operative wound infections out of 60,179 spinal operations giving an incidence of 1.84% of which 0.98% were superficial and 0.87% were deep.6 Mortality from spinal SSIs was 1.06% in a large retrospective study.7 Staphylococcus aureus is responsible for approximately 49% of infections and of those, 38% are methicillin-resistant Staphylococcus aureus (MRSA).5 This is based predominantly on studies from the US.

Risk factors independently associated with SSI after spinal operations include female sex, high body mass index, wound class, American Society of Anesthesiologists (ASA) category, operative duration, insulin-dependent diabetes and prolonged pre-operative steroids.6 Other papers have emphasised comorbidities, including neurological, cardiac and pulmonary disorders, and cancer.7,8

Spinal instrumentation refers to the use of metalware to stabilise the spine. It is associated with biofilm formation and persistent infection despite antibiotics and is thought to increase the rate of SSI by 28%.9 This often warrants additional surgery and more prolonged antibiotics. Metalware removal is controversial and the optimal timing is debated since removal before bony fusion can lead to progressive pain and deformity.10 Many centres choose to retain the metalware in the case of infections (such as the centre in this study). Patel et al calculated a SSI rate of 3.8% after instrumental procedures based on 28,628 patients, double the estimated overall incidence following spinal procedures. The same review revealed a re-operation rate of 89.2% in instrumented SSIs.5

There is evidence for measures to reduce SSIs11 and data on the cost of spinal SSIs will draw more attention to research and the implementation of preventative strategies. The aim of this study was to identify the excess inpatient costs and hospitalisation associated with post-operative spinal infections in a New Zealand setting.

Methods

Patients

The study was conducted at Wellington Regional Hospital (WRH), a tertiary regional referral centre for spinal surgery. In the Wellington region, all inpatients with spinal SSIs are referred and managed at WRH, with spinal surgery only performed at WRH or two other Wellington hospitals. Patients were retrospectively identified using the infectious disease (ID) department inpatient consultation database, which was interrogated for deep SSIs following spinal operations between August 2009 and May 2016 (6 years and 10 months), during which period the ID team was routinely involved in the care of all patients with suspected or confirmed SSI following spinal surgery. Deep SSIs were defined using the CDC criteria.4 Onset of infection was defined as the date of hospital readmission for infection or the date infection was diagnosed when it occurred during the same inpatient stay as the initial spinal surgery. Cases of deep non-instrumented SSI were included with onset of infection after 30 days, beyond the usual CDC time-frame, when treated as a convincing post-operative infection.

Clinical management

Patients were managed under the care of a spinal orthopaedic surgeon with inpatient and outpatient input from an ID physician. Microbiological samples were obtained by aspirate or multiple intraoperative cultures before antibiotic administration when practical. Debridement and metalware retention was undertaken in most cases. Intravenous antibiotics were used until the acute wound infection and drainage stabilised, for most patients 2–6 weeks. Patients were not detained in hospital for IV antibiotics only, as there was a well-established programme for home IV antibiotics. Oral antibiotic switch was made as soon as clinically indicated, guided by microbiological results and using biofilm-active agents as appropriate.

Data extraction and cost estimation

Demographic and clinical data were extracted from hospital electronic patient administration and clinical records, including: patient demographics, procedure date, type of procedure, diagnosis, LOS (including any infection related readmissions), organisms cultured, timing of SSI and surgical and antibiotic management. Cost data for each patient event were extracted from the Capital and Coast District Health Board (CCDHB) clinical costing system (Power Performance Manager, Power Health Solutions). Outpatient IV antibiotic and infusor costs were drawn from the ID pharmacy database and added to the inpatient costs.

For those patients in whom infection was first diagnosed following discharge home from a primary operation and uneventful initial hospital stay, excess costs and LOS were calculated as the costs of the subsequent hospital readmissions related to infection. The follow-up observation period for readmissions was for an average of four years (range 1–8 years).

In those diagnosed with infection during the initial admission, excess costs and LOS were calculated by subtracting the mean cost and LOS for uncomplicated controls without infection from the total cost for their inpatient stay. Control data were extracted from a control group including all patients who, during financial year 2014/2015, had the same ICD-10 Procedure Code as the cases, but without infection or other complication.

The median excess LOS and cost for SSIs following operations with and without metalware were compared statistically with a Mann-Whitney U test using SPSS 25.12 Since the data are not normally distributed, we used median values.

Data on the total number of spinal surgical procedures from 2009–2016 from the three Wellington hospitals performing elective spinal surgery was used to calculate an estimated overall spinal SSI rate.

Literature review

A literature review of PubMed was performed searching for ‘spine’ AND ‘surgery’ AND ‘infection’ AND ‘cost’ to identify other papers that have looked at the inpatient costs associated with deep spinal SSIs. Papers were included if they estimated the hospital costs of deep SSIs after spinal operations. The references of suitable papers were checked for other papers meeting the criteria in an iterative process.

Results

Patients, SSIs and surgical management

Between 2009 and 2016, 28 patients with deep spinal SSIs required an ID consult. Their demographics, surgery and infection onset are shown in Table 1. The primary spinal surgery had been performed in the Wellington Region for 26/28 (93%) patients. Twenty-five patients had undergone operations involving posterior spinal fusions with implantation of spinal metalware. Three patients had undergone spinal discectomy and/or decompression without metalware. Diagnosis of infection was a median of 20.5 days (range 7 to 250 days) following the surgery. Two non-instrumented cases had an onset of infection more than 30 days (31, 74 days) post-operatively. Five infections were diagnosed during the initial admission and 23 resulted in readmission. Twenty-five patients (89%) went on to have surgical intervention to manage the infection, with a median of one operation (range 0–37) in addition to their primary operation. Metalware was retained in 24/25 patients who underwent instrumentation.

Table 1: Patient demographics, surgery and infection onset.

The estimated overall deep SSI infection rate for the three hospitals performing spinal surgery in Wellington was 0.76%.

Microbiology of SSIs

One or more definite or probable pathogens were isolated from intra-operative spinal samples from 25/28 (89%) patients. These included coagulase-negative Staphylococcus spp.(9 patients), methicillin-susceptible Staphylococcus aureus (5), methicillin-resistant Staphylococcus aureus (2), Enterococcus sp. (5), Propionibacterium acnes (2), Proteus mirabilis (2) and one patient each with Klebsiella pneumoniae, Corynebacterium sp., Enterobacter sp. and Pseudomonas aeruginosa.

Controls for patients in whom infection was diagnosed during the initial hospitalisation

For five of the 28 patients, infection was diagnosed during their initial admission. These five patients had undergone one of two categories of surgery, which corresponded (surgery without complication) to ICD-10 Procedure codes 4864500 (posterior spinal fusion, with deformity, three or more levels) and 4865700 (Posterior spinal fusion with laminectomy, two or more levels). There were 16 controls for Procedure 4864500 with an average cost of NZ$40,877.87 and LOS 5.25 days. There were four controls for Procedure 4865700 with an average cost of $42,566.27 and LOS 7.25 days. For each of these five patients, the excess cost and LOS for the initial hospital stay was the difference between the actual total and the corresponding uncomplicated control.

Excess costs and length of stay for patients with spinal surgical site infections

For the 28 patients with spinal SSIs, the excess LOS and excess cost are shown in Table 2. The mean and median excess LOS were 37.1 and 17.4 days respectively. The mean and median excess cost per SSI were NZ$51,356 and $30,964 respectively. Patients with metalware cost an average of $56,172 per SSI with an excess LOS of 40.4 days. Those without metalware cost an average of $11,229 per SSI with an excess LOS of 9.7 days. The excess cost following SSI was significantly more in patients with metalware (p=0.007). While the results suggest an increased excess LOS following SSIs with metalware, the sample size was probably too small to determine a statistical significance (p=0.09).

Table 2: Excess cost and inpatient length of stay (LOS) for patients with spinal infections.

The contributions to the overall excess cost of spinal SSIs are shown in Table 3. Ward costs (29.4%), doctors (24.3%) and operating theatres (18.5%) were the largest contributors.

Table 3: Contributions to the overall excess cost of spinal surgical site infections.

* Includes allied health and community services.
** Includes ward nursing costs.

Literature review

The literature review identified seven papers, all from the USA, that estimated the costs associated with spinal SSIs.13–19 The excess cost estimates ranged between US$12,619 and US$100,666 per SSI (see Table 4). The costs are not adjusted for inflation.

Table 4: Comparison of existing studies estimating the excess cost of deep surgical site infections following spinal surgery.

ˠ includes two superficial infections.
* excess costs for patients in control group included only.

Discussion

The present study showed that while deep spinal SSIs are uncommon, there are substantial inpatient costs and excess LOS associated with them. The observed deep SSI rate for all spinal infections was 0.76%, which is close to the NSQID rate of 0.89% for deep SSIs.6 The mean excess cost of NZ$51,356 broadly agrees with other papers in the literature, but comparisons are difficult due to differences in cost capturing methods and procedures. However, costing data from the US may not be generalisable to New Zealand or elsewhere. This is the first paper we are aware of which documents the cost of spinal SSIs outside of the US.

We confined the current study to the costs of inpatient management, home IV antibiotics and LOS as these had robust data available. This methodology was similar to previous studies but also looked at infusor costs. Kuhns estimated economic costs and Calderone and McGirt calculated some outpatient costs in their studies.13,17,19. The discrepancy in excess costs between the studies compared in the literature review may be in part due to the definitions of SSI used. Three of the studies do not state a definition,14,16,19, and three use non-standard definitions. 15,17,18 Kuhns used the CDC definition, as in this study. 13

Comparison between SSI costs in spine, hip and knee operations is possible. A recent paper looking at hip and knee arthroplasty SSIs in New Zealand with similar methodology and also using the CDC definition for SSI found a mean excess cost of NZ$40,121.20 We observed the excess LOS to be an average of 37.1 days (median 17.4 days), which was comparable to the average 42 days’ excess after knee and hip arthroplasty infections.20 Two USA studies of lumbar SSIs reported excess LOS after spinal SSIs; Parker and Calderone reported an average excess of 12 and 58.6 days respectively.18,19

The costs reported here may be an underestimate. Personal financial and disability costs are not included. Outpatient healthcare costs, such as ID and orthopaedic clinic visits, in this cohort were probably small in comparison to inpatient costs. With biofilm metalware infections, late clinical relapse can occasionally occur years later and warrant further surgical management, beyond a typical follow-up period.

The use of metalware has allowed increasingly complex surgery over several spinal levels. Unfortunately, clinical management of spinal SSIs with metalware is more difficult than SSIs without metalware, particularly where metalware cannot readily be removed. Our finding that SSIs in patients with metalware result in significantly higher excess costs compared with those without is consistent with this.

This study was based in a single region, where the number of spinal SSIs and denominator procedures could be ascertained reliably due to a limited number of spinal surgeons, cooperation between institutions and a single tertiary centre managing all hospitalised deep infections. It is unlikely that any local patients had their infection managed outside the region and excluding the two patients from outside the region only had a modest effect on the overall results.

In our patient cohort, there was a relatively high proportion 25/28 (89%) of patients with a confirmed microbiological diagnosis. A variety of pathogens were observed, including S. aureus, skin organisms, enterococci and aerobic Gram-negative bacilli. This emphasised the importance of obtaining a microbiological diagnosis, particularly when choosing the oral antibiotic agents in the treatment regimen. Greater use of empiric antibiotics would have been anticipated to result in a greater cost and LOS, due to a greater cost of empiric therapy and a potentially greater clinical failure rate.

While a study limitation is the relatively small number of patients (28), this is one of the largest published series of spinal SSIs, and the first outside the US. For non-instrumented cases, the small number and inclusion of clinical infections beyond the 30-day onset in the CDC definition limited comparisons with instrumented cases. Inclusion of outpatient costs was limited to the available reliable costing for IV antibiotic infusors. Existing literature uses average costs, which can be less representative where there is a non-normal distribution, a reason for our having also reported median values and used them in our statistical analysis. The potential for missed cases is a limitation in all such studies, less likely here due to the well-defined region.

In conclusion, there is a substantial excess cost and LOS associated with deep spinal surgical site infections. More awareness of the high costs involved should encourage the implementation of infection prevention strategies and research to reduce the impact of these disabling surgical infections.

Summary

Abstract

Aim

To determine the excess cost and hospitalisation associated with surgical site infections (SSI) following spinal operations in a New Zealand setting.

Method

We identified inpatients treated for deep SSI following primary or revision spinal surgery at a regional tertiary spinal centre between 2009 and 2016. Excess cost and excess length of stay (LOS) were calculated via a clinical costing system using procedure-matched controls.

Results

Twenty-eight patients were identified. Twenty-five had metalware following spinal fusion surgery, while three had non-instrumented decompression and/or discectomy. Five were diagnosed during their index hospitalisation and 23 (82%) were re-admitted. The average excess SSI cost was NZ$51,434 (range $1,398-$262,206.16) and LOS 37.1 days (range 7-275 days). Infections following metalware procedures had a greater excess cost (average $56,258.90 vs. $11,228.61) and LOS (average 40.4 days vs. 9.7 days) than procedures without metalware.

Conclusion

The costs associated with spinal SSI are significant and comparable to a previous New Zealand study of hip and knee prosthesis SSI. More awareness of the high costs involved should encourage research and implementation of infection prevention strategies.

Author Information

- James Barnacle, Principal Medical Officer, Internal Medicine, Daeyang Luke Hospital, Malawi;- Dianne Wilson, Manager, Business Intelligence and Analytics Unit, Grace Neill Block, Wellington Hospital, Wellington; Christopher Little, Infectious Diseas

Acknowledgements

We thank Lisa Woods, School of Mathematics and Statistics, Victoria University, for assistance with statistical analysis.

Correspondence

Nigel Raymond, Infectious Diseases Physician, Infection Service, Level 6, Grace Neill Block, Wellington Hospital, Wellington 6021.

Correspondence Email

nigel.raymond@ccdhb.org.nz

Competing Interests

NR is a longstanding employee of Capital & Coast DHB where the study was conducted (Wellington Hospital). He also is a part-time contractor to Wakefield Hospital (Acurity Health) for Infection Control, who provided data on surgical procedures for the study. There was no internal or external funding for the study.

  1. Klevens RM, Edwards JR, Richards CL, et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Rep. 2007; 122:160–166.
  2. No authors listed. World Health Organization. Report on the burden of endemic health care-associated infection worldwide. 2011. Geneva. http://apps.who.int/iris/bitstream/10665/80135/1/9789241501507_eng.pdf Accessed 22 August 2016.
  3. Kirkland KB, Briggs JP, Trivette SL, et al. The impact of surgical-site infections in the 1990s: attributable mortality, excess length of hospitalization, and extra costs. Infect Control Hosp Epidemiol. 1999; 20:725–30.
  4. Horan TC, Gaynes RP, Martone WJ, et al. CDC definitions of nosocomial surgical site infections, 1992; A modification of CDC definitions of surgical wound infections. Infection Control Hosp Epidemiol. 1992; 13:606-–608.
  5. Patel H, Khoury H, Girgenti D, et al. Burden of surgical site infections associated with select spine operations and involvement of staphylococcus aureus. Surg Infect (Larchmat). 2017; 18:461–473.
  6. Lieber B, Han B, Strom RG, et al. Preoperative predictors of spinal infection within the national surgical quality inpatient database. World Neurosurg. 2016; 89:517–24.
  7. Veeravagu A, Patil CG, Lad SP, Boakye M. Risk factors for postoperative spinal wound infections after spinal decompression and fusion surgeries. Spine (Phila Pa 1976). 2009; 34:1869–1872.
  8. Radcliff KE, Neusner AD, Millhouse PW, et al. What is new in the diagnosis and prevention of spine surgical site infection. Spine J. 2015; 15:336–47.
  9. Smith JS, Shaffrey CI, Sansur CA, et al. Rates of infection after spine surgery based on 108,419 procedures: a report from the scoliosis research society morbidity and mortality committee. Spine (Phila Pa 1976). 2011; 36:556–563.
  10. Rishi RR, Wong AP, Lall RR, et al. Evidence-based management of deep wound infection after spinal instrumentation. J Clin Neurosci. 2015; 22:238–42.
  11. Savage J, Anderson P. An update on the modifiable factors to reduce the risk of surgical site infections. Spine. 2013; 13:1017–28.
  12. IBM SPSS Statistics for Windows, version 25 (IBM Corp., Armonk, N.Y., USA).
  13. Kuhns BD, Lubelski D, Alvin MD, et al. Cost and quality of life outcome analysis of postoperative infections after subaxial dorsal cervical fusions. J Neurosurg Spine. 2015; 22:381–386.
  14. Theologis AA, Demirkiran G, Callahan M, et al. Local intrawound vancomycin powder decreases the risk of surgical site infections in complex adult deformity reconstruction: a cost analysis. Spine. 2014; 39:1875–1880.
  15. Godil SS, Parker SL, O’Neill KR, et al. Comparative effectiveness and cost-benefit analysis of local application of vancomycin powder in posterior spinal fusion. J Neurosurg Spine. 2013; 19:331–5.
  16. Emohare O, Ledonio CG, Hill BW, et al. Cost savings analysis of intrawound vancomycin powder in posterior spinal surgery. Spine J. 2014; 14:2710–2715.
  17. McGirt MJ, Parker SL, Lerner J, et al. Comparative analysis of perioperative surgical site infection after minimally invasive versus open posterior/transforaminal lumbar interbody fusion: analysis of hospital billing and discharge data from 5170 patients. J Neurosurg Spine. 2011; 14:771–778.
  18. Parker SL, Adogwa O, Witham TF, et al. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54:33–37.
  19. Calderone RR, Garland DE, Capen DA, Oster H. Cost of medical care for postoperative spinal infections. Orthop Clin North Am. 1996; 27:171–182.
  20. Gow N, McGuinness C, Morris AJ, et al. Excess cost associated with primary hip and knee joint arthroplasty surgical site infections: a driver to support investment in quality improvement strategies to reduce infection rates. N Z Med J. 2016; 12:51–58.

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Healthcare-associated infections (HAI) are a major source of morbidity, mortality and expense. Surgical site infections (SSI) make up approximately 22% of HAIs in the US1 and 17% in Europe.2 SSIs increase hospital inpatient length of stay (LOS) by a median of two weeks, increase the chance of readmission and re-operation by five times, and double mortality.3

Surgical site infections can be divided into superficial and deep incisional/organ space (henceforth referred to as ‘deep’) as per the Centre for Disease Control and Prevention (CDC) . Superficial infections usually respond well to antibiotics and wound cares. Deep infections involve deep soft tissue or organs/spaces opened or manipulated during the operation and must occur within 30 days of the procedure or within one year if an implant is in situ.4 Deep infections cause the most severe morbidity and are usually managed with surgical debridement, by sending intra-operative tissue samples for microbiology, and intravenous (IV) followed by oral antibiotics targeted at likely or confirmed pathogens.

Surgical site infections are a significant risk of spinal surgery. A recent literature review looking at 425,180 primary spinal procedures calculated a pooled average SSI rate of 1.9%.5 Approximately half of these appear to be deep infections. Lieber et al reviewed the National Surgical Quality Improvement Program Database (NSQID) in the US between 2006 and 2012 and identified 1,110 post-operative wound infections out of 60,179 spinal operations giving an incidence of 1.84% of which 0.98% were superficial and 0.87% were deep.6 Mortality from spinal SSIs was 1.06% in a large retrospective study.7 Staphylococcus aureus is responsible for approximately 49% of infections and of those, 38% are methicillin-resistant Staphylococcus aureus (MRSA).5 This is based predominantly on studies from the US.

Risk factors independently associated with SSI after spinal operations include female sex, high body mass index, wound class, American Society of Anesthesiologists (ASA) category, operative duration, insulin-dependent diabetes and prolonged pre-operative steroids.6 Other papers have emphasised comorbidities, including neurological, cardiac and pulmonary disorders, and cancer.7,8

Spinal instrumentation refers to the use of metalware to stabilise the spine. It is associated with biofilm formation and persistent infection despite antibiotics and is thought to increase the rate of SSI by 28%.9 This often warrants additional surgery and more prolonged antibiotics. Metalware removal is controversial and the optimal timing is debated since removal before bony fusion can lead to progressive pain and deformity.10 Many centres choose to retain the metalware in the case of infections (such as the centre in this study). Patel et al calculated a SSI rate of 3.8% after instrumental procedures based on 28,628 patients, double the estimated overall incidence following spinal procedures. The same review revealed a re-operation rate of 89.2% in instrumented SSIs.5

There is evidence for measures to reduce SSIs11 and data on the cost of spinal SSIs will draw more attention to research and the implementation of preventative strategies. The aim of this study was to identify the excess inpatient costs and hospitalisation associated with post-operative spinal infections in a New Zealand setting.

Methods

Patients

The study was conducted at Wellington Regional Hospital (WRH), a tertiary regional referral centre for spinal surgery. In the Wellington region, all inpatients with spinal SSIs are referred and managed at WRH, with spinal surgery only performed at WRH or two other Wellington hospitals. Patients were retrospectively identified using the infectious disease (ID) department inpatient consultation database, which was interrogated for deep SSIs following spinal operations between August 2009 and May 2016 (6 years and 10 months), during which period the ID team was routinely involved in the care of all patients with suspected or confirmed SSI following spinal surgery. Deep SSIs were defined using the CDC criteria.4 Onset of infection was defined as the date of hospital readmission for infection or the date infection was diagnosed when it occurred during the same inpatient stay as the initial spinal surgery. Cases of deep non-instrumented SSI were included with onset of infection after 30 days, beyond the usual CDC time-frame, when treated as a convincing post-operative infection.

Clinical management

Patients were managed under the care of a spinal orthopaedic surgeon with inpatient and outpatient input from an ID physician. Microbiological samples were obtained by aspirate or multiple intraoperative cultures before antibiotic administration when practical. Debridement and metalware retention was undertaken in most cases. Intravenous antibiotics were used until the acute wound infection and drainage stabilised, for most patients 2–6 weeks. Patients were not detained in hospital for IV antibiotics only, as there was a well-established programme for home IV antibiotics. Oral antibiotic switch was made as soon as clinically indicated, guided by microbiological results and using biofilm-active agents as appropriate.

Data extraction and cost estimation

Demographic and clinical data were extracted from hospital electronic patient administration and clinical records, including: patient demographics, procedure date, type of procedure, diagnosis, LOS (including any infection related readmissions), organisms cultured, timing of SSI and surgical and antibiotic management. Cost data for each patient event were extracted from the Capital and Coast District Health Board (CCDHB) clinical costing system (Power Performance Manager, Power Health Solutions). Outpatient IV antibiotic and infusor costs were drawn from the ID pharmacy database and added to the inpatient costs.

For those patients in whom infection was first diagnosed following discharge home from a primary operation and uneventful initial hospital stay, excess costs and LOS were calculated as the costs of the subsequent hospital readmissions related to infection. The follow-up observation period for readmissions was for an average of four years (range 1–8 years).

In those diagnosed with infection during the initial admission, excess costs and LOS were calculated by subtracting the mean cost and LOS for uncomplicated controls without infection from the total cost for their inpatient stay. Control data were extracted from a control group including all patients who, during financial year 2014/2015, had the same ICD-10 Procedure Code as the cases, but without infection or other complication.

The median excess LOS and cost for SSIs following operations with and without metalware were compared statistically with a Mann-Whitney U test using SPSS 25.12 Since the data are not normally distributed, we used median values.

Data on the total number of spinal surgical procedures from 2009–2016 from the three Wellington hospitals performing elective spinal surgery was used to calculate an estimated overall spinal SSI rate.

Literature review

A literature review of PubMed was performed searching for ‘spine’ AND ‘surgery’ AND ‘infection’ AND ‘cost’ to identify other papers that have looked at the inpatient costs associated with deep spinal SSIs. Papers were included if they estimated the hospital costs of deep SSIs after spinal operations. The references of suitable papers were checked for other papers meeting the criteria in an iterative process.

Results

Patients, SSIs and surgical management

Between 2009 and 2016, 28 patients with deep spinal SSIs required an ID consult. Their demographics, surgery and infection onset are shown in Table 1. The primary spinal surgery had been performed in the Wellington Region for 26/28 (93%) patients. Twenty-five patients had undergone operations involving posterior spinal fusions with implantation of spinal metalware. Three patients had undergone spinal discectomy and/or decompression without metalware. Diagnosis of infection was a median of 20.5 days (range 7 to 250 days) following the surgery. Two non-instrumented cases had an onset of infection more than 30 days (31, 74 days) post-operatively. Five infections were diagnosed during the initial admission and 23 resulted in readmission. Twenty-five patients (89%) went on to have surgical intervention to manage the infection, with a median of one operation (range 0–37) in addition to their primary operation. Metalware was retained in 24/25 patients who underwent instrumentation.

Table 1: Patient demographics, surgery and infection onset.

The estimated overall deep SSI infection rate for the three hospitals performing spinal surgery in Wellington was 0.76%.

Microbiology of SSIs

One or more definite or probable pathogens were isolated from intra-operative spinal samples from 25/28 (89%) patients. These included coagulase-negative Staphylococcus spp.(9 patients), methicillin-susceptible Staphylococcus aureus (5), methicillin-resistant Staphylococcus aureus (2), Enterococcus sp. (5), Propionibacterium acnes (2), Proteus mirabilis (2) and one patient each with Klebsiella pneumoniae, Corynebacterium sp., Enterobacter sp. and Pseudomonas aeruginosa.

Controls for patients in whom infection was diagnosed during the initial hospitalisation

For five of the 28 patients, infection was diagnosed during their initial admission. These five patients had undergone one of two categories of surgery, which corresponded (surgery without complication) to ICD-10 Procedure codes 4864500 (posterior spinal fusion, with deformity, three or more levels) and 4865700 (Posterior spinal fusion with laminectomy, two or more levels). There were 16 controls for Procedure 4864500 with an average cost of NZ$40,877.87 and LOS 5.25 days. There were four controls for Procedure 4865700 with an average cost of $42,566.27 and LOS 7.25 days. For each of these five patients, the excess cost and LOS for the initial hospital stay was the difference between the actual total and the corresponding uncomplicated control.

Excess costs and length of stay for patients with spinal surgical site infections

For the 28 patients with spinal SSIs, the excess LOS and excess cost are shown in Table 2. The mean and median excess LOS were 37.1 and 17.4 days respectively. The mean and median excess cost per SSI were NZ$51,356 and $30,964 respectively. Patients with metalware cost an average of $56,172 per SSI with an excess LOS of 40.4 days. Those without metalware cost an average of $11,229 per SSI with an excess LOS of 9.7 days. The excess cost following SSI was significantly more in patients with metalware (p=0.007). While the results suggest an increased excess LOS following SSIs with metalware, the sample size was probably too small to determine a statistical significance (p=0.09).

Table 2: Excess cost and inpatient length of stay (LOS) for patients with spinal infections.

The contributions to the overall excess cost of spinal SSIs are shown in Table 3. Ward costs (29.4%), doctors (24.3%) and operating theatres (18.5%) were the largest contributors.

Table 3: Contributions to the overall excess cost of spinal surgical site infections.

* Includes allied health and community services.
** Includes ward nursing costs.

Literature review

The literature review identified seven papers, all from the USA, that estimated the costs associated with spinal SSIs.13–19 The excess cost estimates ranged between US$12,619 and US$100,666 per SSI (see Table 4). The costs are not adjusted for inflation.

Table 4: Comparison of existing studies estimating the excess cost of deep surgical site infections following spinal surgery.

ˠ includes two superficial infections.
* excess costs for patients in control group included only.

Discussion

The present study showed that while deep spinal SSIs are uncommon, there are substantial inpatient costs and excess LOS associated with them. The observed deep SSI rate for all spinal infections was 0.76%, which is close to the NSQID rate of 0.89% for deep SSIs.6 The mean excess cost of NZ$51,356 broadly agrees with other papers in the literature, but comparisons are difficult due to differences in cost capturing methods and procedures. However, costing data from the US may not be generalisable to New Zealand or elsewhere. This is the first paper we are aware of which documents the cost of spinal SSIs outside of the US.

We confined the current study to the costs of inpatient management, home IV antibiotics and LOS as these had robust data available. This methodology was similar to previous studies but also looked at infusor costs. Kuhns estimated economic costs and Calderone and McGirt calculated some outpatient costs in their studies.13,17,19. The discrepancy in excess costs between the studies compared in the literature review may be in part due to the definitions of SSI used. Three of the studies do not state a definition,14,16,19, and three use non-standard definitions. 15,17,18 Kuhns used the CDC definition, as in this study. 13

Comparison between SSI costs in spine, hip and knee operations is possible. A recent paper looking at hip and knee arthroplasty SSIs in New Zealand with similar methodology and also using the CDC definition for SSI found a mean excess cost of NZ$40,121.20 We observed the excess LOS to be an average of 37.1 days (median 17.4 days), which was comparable to the average 42 days’ excess after knee and hip arthroplasty infections.20 Two USA studies of lumbar SSIs reported excess LOS after spinal SSIs; Parker and Calderone reported an average excess of 12 and 58.6 days respectively.18,19

The costs reported here may be an underestimate. Personal financial and disability costs are not included. Outpatient healthcare costs, such as ID and orthopaedic clinic visits, in this cohort were probably small in comparison to inpatient costs. With biofilm metalware infections, late clinical relapse can occasionally occur years later and warrant further surgical management, beyond a typical follow-up period.

The use of metalware has allowed increasingly complex surgery over several spinal levels. Unfortunately, clinical management of spinal SSIs with metalware is more difficult than SSIs without metalware, particularly where metalware cannot readily be removed. Our finding that SSIs in patients with metalware result in significantly higher excess costs compared with those without is consistent with this.

This study was based in a single region, where the number of spinal SSIs and denominator procedures could be ascertained reliably due to a limited number of spinal surgeons, cooperation between institutions and a single tertiary centre managing all hospitalised deep infections. It is unlikely that any local patients had their infection managed outside the region and excluding the two patients from outside the region only had a modest effect on the overall results.

In our patient cohort, there was a relatively high proportion 25/28 (89%) of patients with a confirmed microbiological diagnosis. A variety of pathogens were observed, including S. aureus, skin organisms, enterococci and aerobic Gram-negative bacilli. This emphasised the importance of obtaining a microbiological diagnosis, particularly when choosing the oral antibiotic agents in the treatment regimen. Greater use of empiric antibiotics would have been anticipated to result in a greater cost and LOS, due to a greater cost of empiric therapy and a potentially greater clinical failure rate.

While a study limitation is the relatively small number of patients (28), this is one of the largest published series of spinal SSIs, and the first outside the US. For non-instrumented cases, the small number and inclusion of clinical infections beyond the 30-day onset in the CDC definition limited comparisons with instrumented cases. Inclusion of outpatient costs was limited to the available reliable costing for IV antibiotic infusors. Existing literature uses average costs, which can be less representative where there is a non-normal distribution, a reason for our having also reported median values and used them in our statistical analysis. The potential for missed cases is a limitation in all such studies, less likely here due to the well-defined region.

In conclusion, there is a substantial excess cost and LOS associated with deep spinal surgical site infections. More awareness of the high costs involved should encourage the implementation of infection prevention strategies and research to reduce the impact of these disabling surgical infections.

Summary

Abstract

Aim

To determine the excess cost and hospitalisation associated with surgical site infections (SSI) following spinal operations in a New Zealand setting.

Method

We identified inpatients treated for deep SSI following primary or revision spinal surgery at a regional tertiary spinal centre between 2009 and 2016. Excess cost and excess length of stay (LOS) were calculated via a clinical costing system using procedure-matched controls.

Results

Twenty-eight patients were identified. Twenty-five had metalware following spinal fusion surgery, while three had non-instrumented decompression and/or discectomy. Five were diagnosed during their index hospitalisation and 23 (82%) were re-admitted. The average excess SSI cost was NZ$51,434 (range $1,398-$262,206.16) and LOS 37.1 days (range 7-275 days). Infections following metalware procedures had a greater excess cost (average $56,258.90 vs. $11,228.61) and LOS (average 40.4 days vs. 9.7 days) than procedures without metalware.

Conclusion

The costs associated with spinal SSI are significant and comparable to a previous New Zealand study of hip and knee prosthesis SSI. More awareness of the high costs involved should encourage research and implementation of infection prevention strategies.

Author Information

- James Barnacle, Principal Medical Officer, Internal Medicine, Daeyang Luke Hospital, Malawi;- Dianne Wilson, Manager, Business Intelligence and Analytics Unit, Grace Neill Block, Wellington Hospital, Wellington; Christopher Little, Infectious Diseas

Acknowledgements

We thank Lisa Woods, School of Mathematics and Statistics, Victoria University, for assistance with statistical analysis.

Correspondence

Nigel Raymond, Infectious Diseases Physician, Infection Service, Level 6, Grace Neill Block, Wellington Hospital, Wellington 6021.

Correspondence Email

nigel.raymond@ccdhb.org.nz

Competing Interests

NR is a longstanding employee of Capital & Coast DHB where the study was conducted (Wellington Hospital). He also is a part-time contractor to Wakefield Hospital (Acurity Health) for Infection Control, who provided data on surgical procedures for the study. There was no internal or external funding for the study.

  1. Klevens RM, Edwards JR, Richards CL, et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Rep. 2007; 122:160–166.
  2. No authors listed. World Health Organization. Report on the burden of endemic health care-associated infection worldwide. 2011. Geneva. http://apps.who.int/iris/bitstream/10665/80135/1/9789241501507_eng.pdf Accessed 22 August 2016.
  3. Kirkland KB, Briggs JP, Trivette SL, et al. The impact of surgical-site infections in the 1990s: attributable mortality, excess length of hospitalization, and extra costs. Infect Control Hosp Epidemiol. 1999; 20:725–30.
  4. Horan TC, Gaynes RP, Martone WJ, et al. CDC definitions of nosocomial surgical site infections, 1992; A modification of CDC definitions of surgical wound infections. Infection Control Hosp Epidemiol. 1992; 13:606-–608.
  5. Patel H, Khoury H, Girgenti D, et al. Burden of surgical site infections associated with select spine operations and involvement of staphylococcus aureus. Surg Infect (Larchmat). 2017; 18:461–473.
  6. Lieber B, Han B, Strom RG, et al. Preoperative predictors of spinal infection within the national surgical quality inpatient database. World Neurosurg. 2016; 89:517–24.
  7. Veeravagu A, Patil CG, Lad SP, Boakye M. Risk factors for postoperative spinal wound infections after spinal decompression and fusion surgeries. Spine (Phila Pa 1976). 2009; 34:1869–1872.
  8. Radcliff KE, Neusner AD, Millhouse PW, et al. What is new in the diagnosis and prevention of spine surgical site infection. Spine J. 2015; 15:336–47.
  9. Smith JS, Shaffrey CI, Sansur CA, et al. Rates of infection after spine surgery based on 108,419 procedures: a report from the scoliosis research society morbidity and mortality committee. Spine (Phila Pa 1976). 2011; 36:556–563.
  10. Rishi RR, Wong AP, Lall RR, et al. Evidence-based management of deep wound infection after spinal instrumentation. J Clin Neurosci. 2015; 22:238–42.
  11. Savage J, Anderson P. An update on the modifiable factors to reduce the risk of surgical site infections. Spine. 2013; 13:1017–28.
  12. IBM SPSS Statistics for Windows, version 25 (IBM Corp., Armonk, N.Y., USA).
  13. Kuhns BD, Lubelski D, Alvin MD, et al. Cost and quality of life outcome analysis of postoperative infections after subaxial dorsal cervical fusions. J Neurosurg Spine. 2015; 22:381–386.
  14. Theologis AA, Demirkiran G, Callahan M, et al. Local intrawound vancomycin powder decreases the risk of surgical site infections in complex adult deformity reconstruction: a cost analysis. Spine. 2014; 39:1875–1880.
  15. Godil SS, Parker SL, O’Neill KR, et al. Comparative effectiveness and cost-benefit analysis of local application of vancomycin powder in posterior spinal fusion. J Neurosurg Spine. 2013; 19:331–5.
  16. Emohare O, Ledonio CG, Hill BW, et al. Cost savings analysis of intrawound vancomycin powder in posterior spinal surgery. Spine J. 2014; 14:2710–2715.
  17. McGirt MJ, Parker SL, Lerner J, et al. Comparative analysis of perioperative surgical site infection after minimally invasive versus open posterior/transforaminal lumbar interbody fusion: analysis of hospital billing and discharge data from 5170 patients. J Neurosurg Spine. 2011; 14:771–778.
  18. Parker SL, Adogwa O, Witham TF, et al. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54:33–37.
  19. Calderone RR, Garland DE, Capen DA, Oster H. Cost of medical care for postoperative spinal infections. Orthop Clin North Am. 1996; 27:171–182.
  20. Gow N, McGuinness C, Morris AJ, et al. Excess cost associated with primary hip and knee joint arthroplasty surgical site infections: a driver to support investment in quality improvement strategies to reduce infection rates. N Z Med J. 2016; 12:51–58.

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Healthcare-associated infections (HAI) are a major source of morbidity, mortality and expense. Surgical site infections (SSI) make up approximately 22% of HAIs in the US1 and 17% in Europe.2 SSIs increase hospital inpatient length of stay (LOS) by a median of two weeks, increase the chance of readmission and re-operation by five times, and double mortality.3

Surgical site infections can be divided into superficial and deep incisional/organ space (henceforth referred to as ‘deep’) as per the Centre for Disease Control and Prevention (CDC) . Superficial infections usually respond well to antibiotics and wound cares. Deep infections involve deep soft tissue or organs/spaces opened or manipulated during the operation and must occur within 30 days of the procedure or within one year if an implant is in situ.4 Deep infections cause the most severe morbidity and are usually managed with surgical debridement, by sending intra-operative tissue samples for microbiology, and intravenous (IV) followed by oral antibiotics targeted at likely or confirmed pathogens.

Surgical site infections are a significant risk of spinal surgery. A recent literature review looking at 425,180 primary spinal procedures calculated a pooled average SSI rate of 1.9%.5 Approximately half of these appear to be deep infections. Lieber et al reviewed the National Surgical Quality Improvement Program Database (NSQID) in the US between 2006 and 2012 and identified 1,110 post-operative wound infections out of 60,179 spinal operations giving an incidence of 1.84% of which 0.98% were superficial and 0.87% were deep.6 Mortality from spinal SSIs was 1.06% in a large retrospective study.7 Staphylococcus aureus is responsible for approximately 49% of infections and of those, 38% are methicillin-resistant Staphylococcus aureus (MRSA).5 This is based predominantly on studies from the US.

Risk factors independently associated with SSI after spinal operations include female sex, high body mass index, wound class, American Society of Anesthesiologists (ASA) category, operative duration, insulin-dependent diabetes and prolonged pre-operative steroids.6 Other papers have emphasised comorbidities, including neurological, cardiac and pulmonary disorders, and cancer.7,8

Spinal instrumentation refers to the use of metalware to stabilise the spine. It is associated with biofilm formation and persistent infection despite antibiotics and is thought to increase the rate of SSI by 28%.9 This often warrants additional surgery and more prolonged antibiotics. Metalware removal is controversial and the optimal timing is debated since removal before bony fusion can lead to progressive pain and deformity.10 Many centres choose to retain the metalware in the case of infections (such as the centre in this study). Patel et al calculated a SSI rate of 3.8% after instrumental procedures based on 28,628 patients, double the estimated overall incidence following spinal procedures. The same review revealed a re-operation rate of 89.2% in instrumented SSIs.5

There is evidence for measures to reduce SSIs11 and data on the cost of spinal SSIs will draw more attention to research and the implementation of preventative strategies. The aim of this study was to identify the excess inpatient costs and hospitalisation associated with post-operative spinal infections in a New Zealand setting.

Methods

Patients

The study was conducted at Wellington Regional Hospital (WRH), a tertiary regional referral centre for spinal surgery. In the Wellington region, all inpatients with spinal SSIs are referred and managed at WRH, with spinal surgery only performed at WRH or two other Wellington hospitals. Patients were retrospectively identified using the infectious disease (ID) department inpatient consultation database, which was interrogated for deep SSIs following spinal operations between August 2009 and May 2016 (6 years and 10 months), during which period the ID team was routinely involved in the care of all patients with suspected or confirmed SSI following spinal surgery. Deep SSIs were defined using the CDC criteria.4 Onset of infection was defined as the date of hospital readmission for infection or the date infection was diagnosed when it occurred during the same inpatient stay as the initial spinal surgery. Cases of deep non-instrumented SSI were included with onset of infection after 30 days, beyond the usual CDC time-frame, when treated as a convincing post-operative infection.

Clinical management

Patients were managed under the care of a spinal orthopaedic surgeon with inpatient and outpatient input from an ID physician. Microbiological samples were obtained by aspirate or multiple intraoperative cultures before antibiotic administration when practical. Debridement and metalware retention was undertaken in most cases. Intravenous antibiotics were used until the acute wound infection and drainage stabilised, for most patients 2–6 weeks. Patients were not detained in hospital for IV antibiotics only, as there was a well-established programme for home IV antibiotics. Oral antibiotic switch was made as soon as clinically indicated, guided by microbiological results and using biofilm-active agents as appropriate.

Data extraction and cost estimation

Demographic and clinical data were extracted from hospital electronic patient administration and clinical records, including: patient demographics, procedure date, type of procedure, diagnosis, LOS (including any infection related readmissions), organisms cultured, timing of SSI and surgical and antibiotic management. Cost data for each patient event were extracted from the Capital and Coast District Health Board (CCDHB) clinical costing system (Power Performance Manager, Power Health Solutions). Outpatient IV antibiotic and infusor costs were drawn from the ID pharmacy database and added to the inpatient costs.

For those patients in whom infection was first diagnosed following discharge home from a primary operation and uneventful initial hospital stay, excess costs and LOS were calculated as the costs of the subsequent hospital readmissions related to infection. The follow-up observation period for readmissions was for an average of four years (range 1–8 years).

In those diagnosed with infection during the initial admission, excess costs and LOS were calculated by subtracting the mean cost and LOS for uncomplicated controls without infection from the total cost for their inpatient stay. Control data were extracted from a control group including all patients who, during financial year 2014/2015, had the same ICD-10 Procedure Code as the cases, but without infection or other complication.

The median excess LOS and cost for SSIs following operations with and without metalware were compared statistically with a Mann-Whitney U test using SPSS 25.12 Since the data are not normally distributed, we used median values.

Data on the total number of spinal surgical procedures from 2009–2016 from the three Wellington hospitals performing elective spinal surgery was used to calculate an estimated overall spinal SSI rate.

Literature review

A literature review of PubMed was performed searching for ‘spine’ AND ‘surgery’ AND ‘infection’ AND ‘cost’ to identify other papers that have looked at the inpatient costs associated with deep spinal SSIs. Papers were included if they estimated the hospital costs of deep SSIs after spinal operations. The references of suitable papers were checked for other papers meeting the criteria in an iterative process.

Results

Patients, SSIs and surgical management

Between 2009 and 2016, 28 patients with deep spinal SSIs required an ID consult. Their demographics, surgery and infection onset are shown in Table 1. The primary spinal surgery had been performed in the Wellington Region for 26/28 (93%) patients. Twenty-five patients had undergone operations involving posterior spinal fusions with implantation of spinal metalware. Three patients had undergone spinal discectomy and/or decompression without metalware. Diagnosis of infection was a median of 20.5 days (range 7 to 250 days) following the surgery. Two non-instrumented cases had an onset of infection more than 30 days (31, 74 days) post-operatively. Five infections were diagnosed during the initial admission and 23 resulted in readmission. Twenty-five patients (89%) went on to have surgical intervention to manage the infection, with a median of one operation (range 0–37) in addition to their primary operation. Metalware was retained in 24/25 patients who underwent instrumentation.

Table 1: Patient demographics, surgery and infection onset.

The estimated overall deep SSI infection rate for the three hospitals performing spinal surgery in Wellington was 0.76%.

Microbiology of SSIs

One or more definite or probable pathogens were isolated from intra-operative spinal samples from 25/28 (89%) patients. These included coagulase-negative Staphylococcus spp.(9 patients), methicillin-susceptible Staphylococcus aureus (5), methicillin-resistant Staphylococcus aureus (2), Enterococcus sp. (5), Propionibacterium acnes (2), Proteus mirabilis (2) and one patient each with Klebsiella pneumoniae, Corynebacterium sp., Enterobacter sp. and Pseudomonas aeruginosa.

Controls for patients in whom infection was diagnosed during the initial hospitalisation

For five of the 28 patients, infection was diagnosed during their initial admission. These five patients had undergone one of two categories of surgery, which corresponded (surgery without complication) to ICD-10 Procedure codes 4864500 (posterior spinal fusion, with deformity, three or more levels) and 4865700 (Posterior spinal fusion with laminectomy, two or more levels). There were 16 controls for Procedure 4864500 with an average cost of NZ$40,877.87 and LOS 5.25 days. There were four controls for Procedure 4865700 with an average cost of $42,566.27 and LOS 7.25 days. For each of these five patients, the excess cost and LOS for the initial hospital stay was the difference between the actual total and the corresponding uncomplicated control.

Excess costs and length of stay for patients with spinal surgical site infections

For the 28 patients with spinal SSIs, the excess LOS and excess cost are shown in Table 2. The mean and median excess LOS were 37.1 and 17.4 days respectively. The mean and median excess cost per SSI were NZ$51,356 and $30,964 respectively. Patients with metalware cost an average of $56,172 per SSI with an excess LOS of 40.4 days. Those without metalware cost an average of $11,229 per SSI with an excess LOS of 9.7 days. The excess cost following SSI was significantly more in patients with metalware (p=0.007). While the results suggest an increased excess LOS following SSIs with metalware, the sample size was probably too small to determine a statistical significance (p=0.09).

Table 2: Excess cost and inpatient length of stay (LOS) for patients with spinal infections.

The contributions to the overall excess cost of spinal SSIs are shown in Table 3. Ward costs (29.4%), doctors (24.3%) and operating theatres (18.5%) were the largest contributors.

Table 3: Contributions to the overall excess cost of spinal surgical site infections.

* Includes allied health and community services.
** Includes ward nursing costs.

Literature review

The literature review identified seven papers, all from the USA, that estimated the costs associated with spinal SSIs.13–19 The excess cost estimates ranged between US$12,619 and US$100,666 per SSI (see Table 4). The costs are not adjusted for inflation.

Table 4: Comparison of existing studies estimating the excess cost of deep surgical site infections following spinal surgery.

ˠ includes two superficial infections.
* excess costs for patients in control group included only.

Discussion

The present study showed that while deep spinal SSIs are uncommon, there are substantial inpatient costs and excess LOS associated with them. The observed deep SSI rate for all spinal infections was 0.76%, which is close to the NSQID rate of 0.89% for deep SSIs.6 The mean excess cost of NZ$51,356 broadly agrees with other papers in the literature, but comparisons are difficult due to differences in cost capturing methods and procedures. However, costing data from the US may not be generalisable to New Zealand or elsewhere. This is the first paper we are aware of which documents the cost of spinal SSIs outside of the US.

We confined the current study to the costs of inpatient management, home IV antibiotics and LOS as these had robust data available. This methodology was similar to previous studies but also looked at infusor costs. Kuhns estimated economic costs and Calderone and McGirt calculated some outpatient costs in their studies.13,17,19. The discrepancy in excess costs between the studies compared in the literature review may be in part due to the definitions of SSI used. Three of the studies do not state a definition,14,16,19, and three use non-standard definitions. 15,17,18 Kuhns used the CDC definition, as in this study. 13

Comparison between SSI costs in spine, hip and knee operations is possible. A recent paper looking at hip and knee arthroplasty SSIs in New Zealand with similar methodology and also using the CDC definition for SSI found a mean excess cost of NZ$40,121.20 We observed the excess LOS to be an average of 37.1 days (median 17.4 days), which was comparable to the average 42 days’ excess after knee and hip arthroplasty infections.20 Two USA studies of lumbar SSIs reported excess LOS after spinal SSIs; Parker and Calderone reported an average excess of 12 and 58.6 days respectively.18,19

The costs reported here may be an underestimate. Personal financial and disability costs are not included. Outpatient healthcare costs, such as ID and orthopaedic clinic visits, in this cohort were probably small in comparison to inpatient costs. With biofilm metalware infections, late clinical relapse can occasionally occur years later and warrant further surgical management, beyond a typical follow-up period.

The use of metalware has allowed increasingly complex surgery over several spinal levels. Unfortunately, clinical management of spinal SSIs with metalware is more difficult than SSIs without metalware, particularly where metalware cannot readily be removed. Our finding that SSIs in patients with metalware result in significantly higher excess costs compared with those without is consistent with this.

This study was based in a single region, where the number of spinal SSIs and denominator procedures could be ascertained reliably due to a limited number of spinal surgeons, cooperation between institutions and a single tertiary centre managing all hospitalised deep infections. It is unlikely that any local patients had their infection managed outside the region and excluding the two patients from outside the region only had a modest effect on the overall results.

In our patient cohort, there was a relatively high proportion 25/28 (89%) of patients with a confirmed microbiological diagnosis. A variety of pathogens were observed, including S. aureus, skin organisms, enterococci and aerobic Gram-negative bacilli. This emphasised the importance of obtaining a microbiological diagnosis, particularly when choosing the oral antibiotic agents in the treatment regimen. Greater use of empiric antibiotics would have been anticipated to result in a greater cost and LOS, due to a greater cost of empiric therapy and a potentially greater clinical failure rate.

While a study limitation is the relatively small number of patients (28), this is one of the largest published series of spinal SSIs, and the first outside the US. For non-instrumented cases, the small number and inclusion of clinical infections beyond the 30-day onset in the CDC definition limited comparisons with instrumented cases. Inclusion of outpatient costs was limited to the available reliable costing for IV antibiotic infusors. Existing literature uses average costs, which can be less representative where there is a non-normal distribution, a reason for our having also reported median values and used them in our statistical analysis. The potential for missed cases is a limitation in all such studies, less likely here due to the well-defined region.

In conclusion, there is a substantial excess cost and LOS associated with deep spinal surgical site infections. More awareness of the high costs involved should encourage the implementation of infection prevention strategies and research to reduce the impact of these disabling surgical infections.

Summary

Abstract

Aim

To determine the excess cost and hospitalisation associated with surgical site infections (SSI) following spinal operations in a New Zealand setting.

Method

We identified inpatients treated for deep SSI following primary or revision spinal surgery at a regional tertiary spinal centre between 2009 and 2016. Excess cost and excess length of stay (LOS) were calculated via a clinical costing system using procedure-matched controls.

Results

Twenty-eight patients were identified. Twenty-five had metalware following spinal fusion surgery, while three had non-instrumented decompression and/or discectomy. Five were diagnosed during their index hospitalisation and 23 (82%) were re-admitted. The average excess SSI cost was NZ$51,434 (range $1,398-$262,206.16) and LOS 37.1 days (range 7-275 days). Infections following metalware procedures had a greater excess cost (average $56,258.90 vs. $11,228.61) and LOS (average 40.4 days vs. 9.7 days) than procedures without metalware.

Conclusion

The costs associated with spinal SSI are significant and comparable to a previous New Zealand study of hip and knee prosthesis SSI. More awareness of the high costs involved should encourage research and implementation of infection prevention strategies.

Author Information

- James Barnacle, Principal Medical Officer, Internal Medicine, Daeyang Luke Hospital, Malawi;- Dianne Wilson, Manager, Business Intelligence and Analytics Unit, Grace Neill Block, Wellington Hospital, Wellington; Christopher Little, Infectious Diseas

Acknowledgements

We thank Lisa Woods, School of Mathematics and Statistics, Victoria University, for assistance with statistical analysis.

Correspondence

Nigel Raymond, Infectious Diseases Physician, Infection Service, Level 6, Grace Neill Block, Wellington Hospital, Wellington 6021.

Correspondence Email

nigel.raymond@ccdhb.org.nz

Competing Interests

NR is a longstanding employee of Capital & Coast DHB where the study was conducted (Wellington Hospital). He also is a part-time contractor to Wakefield Hospital (Acurity Health) for Infection Control, who provided data on surgical procedures for the study. There was no internal or external funding for the study.

  1. Klevens RM, Edwards JR, Richards CL, et al. Estimating health care-associated infections and deaths in U.S. hospitals, 2002. Public Health Rep. 2007; 122:160–166.
  2. No authors listed. World Health Organization. Report on the burden of endemic health care-associated infection worldwide. 2011. Geneva. http://apps.who.int/iris/bitstream/10665/80135/1/9789241501507_eng.pdf Accessed 22 August 2016.
  3. Kirkland KB, Briggs JP, Trivette SL, et al. The impact of surgical-site infections in the 1990s: attributable mortality, excess length of hospitalization, and extra costs. Infect Control Hosp Epidemiol. 1999; 20:725–30.
  4. Horan TC, Gaynes RP, Martone WJ, et al. CDC definitions of nosocomial surgical site infections, 1992; A modification of CDC definitions of surgical wound infections. Infection Control Hosp Epidemiol. 1992; 13:606-–608.
  5. Patel H, Khoury H, Girgenti D, et al. Burden of surgical site infections associated with select spine operations and involvement of staphylococcus aureus. Surg Infect (Larchmat). 2017; 18:461–473.
  6. Lieber B, Han B, Strom RG, et al. Preoperative predictors of spinal infection within the national surgical quality inpatient database. World Neurosurg. 2016; 89:517–24.
  7. Veeravagu A, Patil CG, Lad SP, Boakye M. Risk factors for postoperative spinal wound infections after spinal decompression and fusion surgeries. Spine (Phila Pa 1976). 2009; 34:1869–1872.
  8. Radcliff KE, Neusner AD, Millhouse PW, et al. What is new in the diagnosis and prevention of spine surgical site infection. Spine J. 2015; 15:336–47.
  9. Smith JS, Shaffrey CI, Sansur CA, et al. Rates of infection after spine surgery based on 108,419 procedures: a report from the scoliosis research society morbidity and mortality committee. Spine (Phila Pa 1976). 2011; 36:556–563.
  10. Rishi RR, Wong AP, Lall RR, et al. Evidence-based management of deep wound infection after spinal instrumentation. J Clin Neurosci. 2015; 22:238–42.
  11. Savage J, Anderson P. An update on the modifiable factors to reduce the risk of surgical site infections. Spine. 2013; 13:1017–28.
  12. IBM SPSS Statistics for Windows, version 25 (IBM Corp., Armonk, N.Y., USA).
  13. Kuhns BD, Lubelski D, Alvin MD, et al. Cost and quality of life outcome analysis of postoperative infections after subaxial dorsal cervical fusions. J Neurosurg Spine. 2015; 22:381–386.
  14. Theologis AA, Demirkiran G, Callahan M, et al. Local intrawound vancomycin powder decreases the risk of surgical site infections in complex adult deformity reconstruction: a cost analysis. Spine. 2014; 39:1875–1880.
  15. Godil SS, Parker SL, O’Neill KR, et al. Comparative effectiveness and cost-benefit analysis of local application of vancomycin powder in posterior spinal fusion. J Neurosurg Spine. 2013; 19:331–5.
  16. Emohare O, Ledonio CG, Hill BW, et al. Cost savings analysis of intrawound vancomycin powder in posterior spinal surgery. Spine J. 2014; 14:2710–2715.
  17. McGirt MJ, Parker SL, Lerner J, et al. Comparative analysis of perioperative surgical site infection after minimally invasive versus open posterior/transforaminal lumbar interbody fusion: analysis of hospital billing and discharge data from 5170 patients. J Neurosurg Spine. 2011; 14:771–778.
  18. Parker SL, Adogwa O, Witham TF, et al. Post-operative infection after minimally invasive versus open transforaminal lumbar interbody fusion (TLIF): literature review and cost analysis. Minim Invasive Neurosurg. 2011; 54:33–37.
  19. Calderone RR, Garland DE, Capen DA, Oster H. Cost of medical care for postoperative spinal infections. Orthop Clin North Am. 1996; 27:171–182.
  20. Gow N, McGuinness C, Morris AJ, et al. Excess cost associated with primary hip and knee joint arthroplasty surgical site infections: a driver to support investment in quality improvement strategies to reduce infection rates. N Z Med J. 2016; 12:51–58.

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