Healthcare-associated infections (HAI) are associated with significant morbidity and mortality.1,2 Surgical site infections (SSI) are the second most frequent type of HAI in European countries, the US and other similar high-income countries such as New Zealand.3 Patients experiencing an SSI have longer stays in hospital, increased mortality and higher healthcare-related costs when compared to those without SSI.4 Patients exposed to surgery carry twice the overall HAI burden compared to those patients not exposed to surgery; almost half attributable to SSI.5 Local Auckland data from the late 1990s estimated that the annual cost of HAI for surgical and medical admissions to all hospitals in New Zealand was NZD$137 million.4 Active surveillance and reporting of HAI is associated with a significant reduction in HAI events.6 Moreover, surveillance and reporting of SSI leads to a mean reduction in their incidence.7–18 An independent cost-benefit analysis conducted in 2011 suggested a contemporary surveillance programme and dissemination of the results was highly likely to lead to significant reductions in SSI rates in New Zealand, and that a reduction in rates of approximately 8% a year was possible.19

Due to the evidence for significant patient benefit and reduced healthcare costs, a national SSI surveillance programme was established in 2013. As described previously in this journal, the New Zealand Surgical Site Infection Improvement Programme, known as the SSII Programme, was instituted by the Health Quality & Safety Commission (the Commission) with an initial focus on hip and knee arthroplasties, now expanded to cardiac procedures.20 The programme adopted an evidence-based three-pronged approach to reduce the incidence of surgical site infections in New Zealand, consisting of surveillance of surgical site infections via a nationwide surveillance system and data warehouse called National Monitor; promotion of nationwide adherence to specific evidence-based practices proven to reduce the incidence of SSI; and monitoring and reporting of changed practice and its effects on outcomes.

This study set out to determine the magnitude of improvement, if any, since institution of the programme. We report results from July 2013 until June 2017.

Method

The purpose, background, structure and rationale for the NZ SSII Programme have been described previously in this journal.20 Full details of the methods, data collection forms, definitions and interventions are available on the Commission’s website.21

The SSII Programme is ongoing and has a three-pronged approach to reduce the incidence of SSI in New Zealand. In summary, these are:20

1. Surveillance: establishing a nationwide surveillance system and data warehouse called National Monitor, hosted by Canterbury DHB, initially targeting hip and knee arthroplasties, and expanded since 2015 to include selected cardiac surgery procedures;
   
2. Practice change: promoting consistent adherence to evidence-based practices proven to reduce the incidence of SSI; and,
   
3. Monitoring changed practice and its effects: measuring and providing feedback on the implementation of these best practices, and their effects on the rate of SSI. This includes an estimate of the value to the system, and to patients, due to effects on outcomes.
   

We briefly consider each of these strategies in turn.

Surveillance

SSI surveillance for publicly funded hip and knee arthroplasty in New Zealand hospitals utilises National Monitor, a data warehouse developed by ICNet, provider of infection prevention and control surveillance software to surveillance programmes in the UK, the US, Australia, Scotland and Wales.22 Trialled with eight DHBs in a development phase in early 2013, National Monitor was rolled out to remaining DHBs in July 2013.20

Only DHB-funded procedures, performed in either the DHB or other facility on a DHB contract, are included. Privately funded procedures performed in private surgical hospitals are not included in the surveillance. The US Centers for Disease Control and Prevention’s (CDC) National Healthcare Safety Network (NHSN) definitions for SSI are used.20,23 These provide precise definitions of a surgical site infection and their classifications (superficial, deep and organ space) and make clear appropriate exclusions.21,24

Due to the availability of different systems in DHBs, some DHBs use an electronic surveillance system for case identification, but the majority of DHBs use either a manual or hybrid system containing both electronic and manual components. To ensure that all eligible procedures are included in the surveillance, multiple sources of data are reviewed, including patient management systems, operating theatre records and emergency theatre records. Potential SSI cases are identified by surveillance of readmissions within 30 and 90 days after any specified hip and knee arthroplasty procedures funded by the DHB (including those in a private setting). Data capture takes place via hospital patient management systems using New Zealand’s unique patient identifier, the national health index (NHI) number, as well as review of microbiology results, and liaison with operating room and ward staff, infectious disease physicians and microbiologists. Some DHBs also have the ability to run reports identifying patients that have admissions longer than the average length of stay to further review for infection.

The NHI allows linkage of all encounters with a health provider, including inpatient, outpatient and community-based care as well as readmissions.

Patient records of all potential cases are reviewed to determine if NHSN SSI definitions are met. Bacteraemia cases, for example, are also reviewed to determine if cases meet SSI criteria. Precision in definition is essential to having a consistent dataset that can allow comparison over time. Cellulitis, for example, does not in itself count as an SSI, and SSIs following manipulation of the operative site (such as aspiration of a hematoma, for example) are excluded from the definition of SSIs, as the course of infection is no longer clear. In situations of uncertainty the SSII Programme clinical lead or infection prevention and control (IPC) nurse specialist seeks further information from the operating surgeon. SSIs resulting from procedures performed at other hospitals are communicated by IPC staff for appropriate attribution and learning for quality improvement.24 The SSI minimum dataset is completed for procedures that fulfil the NHSN criteria for SSI and are uploaded onto the online form in National Monitor by the data transfer team member. SSI data are submitted by DHBs each quarter, and independent data checks are made by the national SSII Programme team for anomalies and/or incomplete information to increase comprehensiveness of the database. Any additional information needed is requested from IPC staff at DHBs.

Training on application of the NHSN definitions included formal training at programme outset, as well as ongoing regular case review sessions at regional meetings and direct support from project team members. DHB IPC staff work with multidisciplinary teams at their organisations to ensure SSI case review is thorough and in line with definitions.

The feedback portion of surveillance results is crucial to reducing SSI rates. Surveillance reports subsequently generated are disseminated widely, to the expert faculty group, heads of orthopaedic departments, IPC staff and senior leadership at all DHBs, and published on the Commission’s website.

Data elements recorded within National Monitor and detailed information on definitions, data collection, validation and quality assurance protocols are available in the Orthopaedics Surgery Implementation Manual (http://www.hqsc.govt.nz/assets/Infection-Prevention/Surgical-Site-Infection-Surveillance/SSII-implementation-manual-Apr-2016.pdf).25

Practice change

A three-fold package of evidence-based interventions was implemented by the programme.

1. Administration of the right antibiotic in the right dose at the right time—evidence recommends ≥2g of cefazolin intravenously for routine antibiotic prophylaxis for hip and knee replacements (≥1.5g dose of cefuroxime is an acceptable alternative).25 For primary procedures prophylaxis should be administered as a single dose within 60 minutes before the initial incision (“knife to skin”) is made.20 This is in line with the World Health Organization (WHO) Surgical Safety Checklist26 item that checks if antibiotic prophylaxis has been given within the 60 minutes before knife to skin.
   
2. Skin antisepsis—ensuring that appropriate skin antisepsis before incision takes place: evidence recommends a preparation including 70% alcohol (eg, chlorhexidine gluconate/alcohol or povidone-iodine/alcohol solution).27
   
3. Clipping not shaving—ensuring that clipping of hair overlying surgical wound sites is standard practice, avoiding shaving.20
   

Supporting practice change

To improve staff uptake, engagement and awareness, we implemented multi-pronged approaches to engage healthcare workers and encourage their active participation in surveillance and quality improvement activities.

A clinician with expertise in IPC was appointed as the national clinical lead of the SSII Programme to facilitate progress of the programme and provide regular updates to various stakeholders. Expert faculty groups were formed; these are multi-disciplinary teams comprised of surgeons, anaesthetists, perioperative nurses and IPC nurses from across New Zealand. The clinical lead also participates in peer-to-peer conversations with doctors around the country, via grand rounds, for example, and by invitation.

We conducted a national campaign around SSI prevention, including provision of a series of webinars focused on surveillance methods, quality improvement interventions and engaging consumers. This campaign also developed and distributed posters, patient education brochures and videos.

A quality improvement advisor was designated as a resource for the national SSII Programme to work with individual DHBs to progress quality improvement activities. A 12-month Quality Improvement Facilitator course was offered to an IPC nurse from each DHB with a specific focus on SSI reduction. This course included face-to-face learning sessions, regional meetings and monthly webinars that provide training in quality-improvement methodologies and tools. Each participant conducted an SSI-related project at their DHB and learnings and ideas were shared among this group throughout the course.

Monitoring changed practice and its effects

The programme measures and reports the effects of compliance with the process measures below on one outcome measure: surgical site infections per 100 hip and knee procedures for orthopaedic surgery. Compliance with process measures is calculated from the National Monitor dataset, and collectively these measures are known as a Quality and Safety Marker (QSM)28 and are publicly reported quarterly by DHB on the Commission’s website.29

Process measures

1. Correct timing for antibiotic prophylaxis—was the antibiotic given within 60 minutes before knife to skin in all primary procedures? The QSM target is 100%.
   
2. Right antibiotic in the right dose—was cefazolin ≥2g used? (Cefuroxime ≥1.5g is also acceptable). To allow for instances of beta-lactam allergy, the QSM threshold is 95%.
   
3. Appropriate skin antisepsis—has a 70% alcohol/chlorhexidine or 70% alcohol/povidone-iodine solution been used? This should always occur, so the QSM target is 100%. (Due to continual high compliance with 99% or more procedures meeting the threshold every surveillance quarter, this measure was retired in the last quarter of 2016).30
   

Outcome measure

The main outcome measure collected and monitored by the programme is proportion of SSI per 100 procedures for total hip and total knee arthroplasties, including revision procedures, where the SSI is defined as superficial, deep incisional or joint space, occurring in hospital (in hospital refers to an infection occurring during the initial admission or requiring readmission within 30 days (superficial) or within 90 days (deep and organ space) post-operation). Infection rates are monitored using statistical process control (SPC) and results presented as run charts, or run charts with limits, known as control charts.31,32

Estimates of the value of reducing SSI are part of the Commission’s measurement of this programme. The additional cost of treating an SSI in hip and knee replacements has been estimated at between NZD$40,000 and NZD$112,000.4,20,33 Quantification of the value of an avoided SSI to the patient is necessarily approximate. However, SSI have been estimated to cost the patient 0.5 disability-adjusted life years (DALYs).34 (The DALY combines the likely shortening of life (years of life lost) with the loss of quality of life (years of life disabled) to measure the effect on individuals and populations of specific illnesses and harms.35,36) The current New Zealand estimate of the Value of a Statistical Life (VoSL) is $4 million (based on what New Zealanders state they are willing to pay in improving roads to save a life). Using methodology from the Accident Compensation Corporation (ACC) to calculate the value of a year of healthy life (or avoided DALY) from this figure, each avoided DALY provides NZD$181,000 worth of value.37 Hence each avoided surgical site infection provides approximately NZD$90,000 of value for each patient.

More detailed results covering these and other aspects of the programme are published in quarterly reports, the most recent covering the programme through to September 2017.38

Results

Change in practice

The QSM indicators show that for all three process measures there has been an increase in compliance between quarter 3 2013 and quarter 4 2016 (see Figure 1). Currently, more than 90% of hip and knee replacement patients receive all three interventions, up from 40% at the commencement of the programme.

Figure 1: Compliance with the three SSI prevention interventions for publicly funded hip and knee replacement procedures, by quarter (Q), 2013 to 2017.

Documentation of the right antibiotic in the right dose was, at greater than 98%, high from programme outset, and the majority of improvement was due to improved compliance. While non-documentation of timing was higher initially at 8%, this fell significantly over the first five quarters to 2.5%. Failure to document the use of skin preparation fell in the first five quarters from 1.3% to 0.2%. From then improvement in compliance was due to increasing intervention adherence.

The number of DHBs achieving the nationally mandated thresholds for the three QSM process measures have increased over the period of the study (see Figure 2).

Figure 2: Number of DHBs (maximum 20) achieving nationally mandated thresholds for achievement of the three QSM process measures, by quarter, 2013 to 2017.

Change in outcome measure: reduction in SSI rate over time

The median surgical site infection rate has shown a significant improvement, dropping to 0.91% since June 2015, compared with 1.36% during the baseline period of April 2013 to March 2014. Figure 3 shows the change in SSI rate in “p chart” format. There is a shift in overall rate from the third quarter 2015, ie, from August 2015, identified by a run of six consecutive points below the initial median rate.39,40 This special cause variation in the infection rate was sustained from June 2015 to March 2017. The likelihood of this occurring by chance is <0.01.

Figure 3: Run chart showing proportion of hip and knee replacement surgeries which had a surgical site infection by month, New Zealand, 2013–16.

The majority—approximately 66%—of SSIs in the data were deep and organ space.

The two “spikes” in February and September 2016 are higher outliers, which indicate one-time occurrences of a special cause (more than three standard deviations from the mean). The reasons for these two special cause variations are difficult to ascertain, but examination of the September DHB-level data shows the number of SSI increased by one or two cases in seven DHBs compared with their baseline levels of zero or one case per month.

During the period of the study there was no reduction in the proportion of patients included in the analysis who were identified as morbidly obese (body mass index (BMI) ≥40) (see Figure 4).

Figure 4: Proportion of patients with BMI ≥40, by quarter, March 2013–June 2017.

The reduction in the SSI rate to 0.91% equates to approximately 55 fewer infections between August 2015 and June 2017. There were 30 fewer observed SSI in the 2015/2016 financial year than we would expect from the baseline data (a 24% reduction), and 25 fewer observed SSI in the 2016/2017 financial year (a 19% reduction on baseline data). This reduction equates to, conservatively, savings of NZD$2.2 million in avoided treatment for the period,4 and avoided DALYs of NZD$5 million.

To further test this apparent shift, a difference in proportion test on the SSI rate pre- and post- the shift point in August 2017 was conducted and showed a statistically significant reduction (odds ratio 0.78, 95% confidence interval 0.65–0.94, p=0.01) (see Table 1).

Table 1: Surgical site infection rates before and after run chart shift point (August 2017).

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Discussion

The introduction of the SSII Programme has resulted in an increase in compliance with three key process measures, associated with a reduction in the proportion of hip and knee replacement surgeries that had an SSI from August 2015. This reduction has been sustained to June 2017. The median SSI rate has shown a significant improvement, dropping to 0.91% since June 2015, compared with 1.36% during the baseline period of April 2013 to March 2014 (p<0.01).

This result is in line with international findings. SSI surveillance involves the collection and provision of reliable data allowing clinicians to make meaningful comparisons between local incidence rates and national benchmarks, and to monitor changes in local rates over time. Strong international evidence from the Netherlands, Germany and France among others has shown that the monitoring and reporting of SSIs is associated with a mean reduction in their incidence.7–18 As Krukowski and Bruce concluded in 2008, “it has been clear for almost three decades that the routine collection and dissemination of rates of surgical site infection results indirectly in a worthwhile reduction.”7 Surveillance serves to inform and prompt the needed actions, but these actions must be implemented for improvement to occur. The universal, standardised application of practices proven to reduce the incidence of SSIs is required to see nationwide improvement in infection rates. Before promotion of the interventions of the SSII Programme there had been inconsistent implementation of clinical practices associated with a reduction in SSI throughout New Zealand—eliminating unjustified variation in practice is a key element of quality improvement.41,42 The QSM indicators show that for all process measures there has been an increase in compliance with expected best practice to the extent that this is now nearly universal across public hospitals in New Zealand. Further, in excess of 90% of hip and knee replacement patients now receive all three interventions, an increase from 40% in the third quarter of 2013. The use of these best practice interventions has effectively been undertaken as a “bundle”43 by New Zealand hospitals. The increasing proportions of local units meeting these performance thresholds demonstrates that this improving compliance with good practice was seen across the country as unwarranted variation decreased.

Estimates of value are always approximate but using conservative estimates from the literature suggests the reduced number of approximately 55 SSI cases in hip and knee arthroplasty in New Zealand between August 2015 and June 2017 has contributed to savings of NZD$2.2 million in avoided treatment. However, as Grimer and colleagues note, deep infection following an arthroplasty is not only expensive to manage, it is a “disaster for the patient”.44 Understanding the financial benefits of avoiding infection is important but can obscure the harm and trauma caused to the individual if this is not quantified as well. Estimates using VoSL and ACC methodologies of reduced SSI in New Zealand hip and knee arthroplasty patients yields an estimate of avoided DALYs of NZD$5 million between August 2015 and June 2017.

Limitations

Infection rates have been analysed using statistical process control (SPC) approaches. SPC is a statistical technique with origins in manufacturing and industry, developed from the work of Walter Shewhart and W Edwards Deming from the 1920s onwards.45 These approaches are now widely used in healthcare,39,40,46 quality improvement projects,31,32,47 IPC48,49 and SSI reduction.50,51,52 SPC is a useful approach to monitoring the effects of improvement interventions and has the advantages in allowing quicker identification of trends and more timely decision making.31,32 Subsidiary before-and-after analyses support the reduction in SSI rate (see Table 1).

Not all the reduction in the SSI rate may be due to the greatly improved compliance with best practice. Other changes in practice following dissemination and discussion of local SSI surveillance data may have occurred, such as improved patient temperature control, theatre clothing, control of theatre traffic, wound dressing policy, weight reduction before surgery and health practitioner hand hygiene, all of which have the potential to reduce SSI. The potential effects of changes in casemix and proportion of patients presenting with higher BMI over the period of the study was examined in light of recent findings of a statistically significant association between higher patient BMI and early periprosthetic joint infection following total hip and knee arthroplasty (BMI ≥40kg/m2 odds ratio 5.62, 95% CI 2.25-14.0).53 Figure 4 shows that there has been no decrease in the proportion of patients with BMI ≥40kg/m2, indicating that the reduction in SSI is not a reflection of reduced risk.

The reasons for the two special cause variations are difficult to ascertain, but examination of the September DHB-level data shows the number of SSI increased by one or two cases in seven DHBs compared with their baseline levels of zero or one case per month. Closer examination of the SSIs in these outlier months does not point to any obvious reason for the two peaks. There do not appear to be more high-risk patients in these months, and the relative proportions of the type of SSI (superficial, deep, organ space) are identical to the period as a whole. Revision procedures accounted for 8% of all procedures included in the analysis.

Strengths

The NHI linkage across all encounters with a health provider, including inpatient, outpatient and readmissions, has strengthened our ability to capture cases.

Where to next?

The data showing a 24% reduction in observed SSI in the 2015/2016 financial year, and the 19% reduction in the 2016/2017 financial year, compare favourably with the 2011 cost-benefit analysis finding that a reduction in rates of approximately 8% a year was possible.19 This is an ongoing programme and the challenge now is to maintain these gains. New Zealand SSI rates are still double those seen in the UK and we need to consolidate and build on this initial success.54 The most commonly isolated pathogen and cause of SSI globally and in New Zealand is Staphylococcus aureus,55,56 accounting for about 30% of orthopaedic SSI identified in New Zealand patients, and coagulase-negative staphylococci about 13%.57,58 The SSII Programme is currently working on nationwide implementation of a standardised anti-staphylococcal bundle derived from a Royal Australasian College of Surgeons (RACS) systematic review and meta-analysis59 and endorsed by the Strategic Infection Prevention & Control Advisory Group (SIPCAG).60

The SSII Cardiac Programme has also observed opportunities to improve prophylaxis, particularly timing. S. aureus is also the common pathogen isolated and interventions to reduce S. aureus infections will also benefit cardiac patients. It is probable that the orthopaedic and cardiac findings on prophylaxis and skin preparations are occurring in other surgical specialties. Our hope is that, by showing how practice can change and result in better patient outcomes, other surgical teams will utilise the methods proven to work here to reduce the risk of SSI in their patients.

Conclusion

These data show that the introduction of a nationwide SSI reduction programme for primary hip and knee arthroplasties in New Zealand resulted in an increase in compliance across the country with expected best practice, that was associated with a reduction in incidence of SSI from a median of 1.36% during the baseline period of April 2013 to March 2014 to 0.91% since June 2015; a reduction sustained to June 2017.

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