Background
Surgical site infections are feared complications of spinal surgery, the volume of which is expected to increase every year worldwide [
1]. Likewise, community-acquired spinal infections (SIs) are associated with increased morbidity and costs and prolonged hospital stay for the patients [
1]. Most scientific papers are interested in the epidemiology of SI and risk factors for surgical site infections after spinal surgery [
2], occurring at 1–3% [
2‐
4], rather than the modalities and outcomes of treatment. Risk factors leading to infection may be multiple. To cite an example, according to our University Spine Center at the Balgrist University Hospital in Zurich, associated risk factors are a high serum creatinine level, blood loss, or steroid use. Some of these risk factors influence the occurrence of infection only indirectly and act as a confounding element. For example, fusion surgery, particularly if it involves the lumbosacral spine, and length of surgery are associated with high blood loss [
2], which itself may become an independent risk factor for infection. This remains the domain of infection control.
In contrast, we are interested if we can streamline antibiotic therapy after the occurrence of infection, especially by shortening its duration. Such results can be of high value for clinicians. So far, the literature on antibiotic regimens in SI is very sparse and strongly eminence-based (instead of being based on evidence). Most experts recommend a minimum (intravenous) antibiotic course duration of 2–4 weeks, often followed by prolonged oral antimicrobial regimens in case of infected osteosynthesis material that was kept in place [
1]. Comparative data supporting these individual therapeutic recommendations are lacking. Indeed, one coauthor of the current project analyzed long-term remission with an emphasis on surgical and antibiotic-related parameters. The patients had a median of two surgical debridements with a median duration of antibiotic therapy of 8 weeks, during which the therapy was delivered parenterally for 2 weeks. In 53 cases (80%), the episodes were in complete remission. In cluster-controlled multivariate Cox regression analysis adjusting for the case mix, the duration of postsurgical antibiotic therapy was completely indecisive regarding the “remission of infection” or “mechanical sequelae” [
1]. Especially, the following clinically important variables were all unrelated to remission: number of surgical interventions (hazard ratio [HR], 0.9; 95% confidence interval, 0.8–1.1), infection due to
Staphylococcus aureus (HR, 0.9; 0.8–1.1), infection due to local antibiotic therapy (HR, 1.2; 0.6–2.4), and duration of total (HR, 1.0; 0.99–1.01) or just parenteral (HR, 1.0; 0.99–1.01) antibiotic use [
1].
If there is no benefit to long duration antibiotic therapy, it would be important to limit the use of antibiotic agents to avoid furthering the problem of antibiotic resistance and adverse events, because the incidence of adverse events related to antibiotic therapy (substantial adverse events in up to 29% of all treatment episodes [
5]) and costs genuinely increase with longer duration of antimicrobial administration [
5]. We equally think that as long as oral antibiotics are used with good bioavailability and bone tissue diffusion, the antimicrobial treatment can be considerably shortened for the benefit of patients and the healthcare sector [
6].
Discussion
With our cohort in two embedded RCTs, we seek to demonstrate clinically relevant noninferiority of a shorter systemic antibiotic treatment in adult patients with SI with and without implants [
1] and, independently of the surgical drainage technique, the number of debridements, underlying individual chronic immune suppression, the infection localization, or the pathogens. Importantly, all study participants will have accompanying multidisciplinary surgical, re-educational, internist, and infectious disease treatment and follow-up. We will equally collect intraoperative soft tissues and bone for future (laboratory) studies and assess adverse events, overall costs, functional outcomes, and the dynamic changes in nutritional status of the infected patients in relation to their therapy and outcomes. The studies will start in Zurich but are expandable to other study centers with experience in treating SI.
The primary outcome is remission at the last follow-up, but the RCT can be adjusted for different important variables, such as the number of surgical debridements, the use of a negative pressure therapy, administration of a parenteral antibiotic regimen, or the total duration of antibiotic therapy. As in many fields of septic orthopedic surgery, the number of surgical debridements does not formally influence remission rates, which has been shown for chronic osteomyelitis [
10], septic native joint arthritis [
11], fracture device infections [
12], infected open fractures [
11], or prosthetic joint infections [
13]. There is very little evidence to guide surgical treatment of patients who require a single versus multiple debridements. Dipaola et al. [
14] developed a predictive model for spinal surgical site infections based on 128 infected patients. Among 30 clinical variables analyzed, and despite the retrospective nature of their analysis, they validated 4 variables as being strongly predictive regarding the necessity of multiple debridements: infection due to methicillin-resistant
Staphylococcus aureus, bacteremic disease, posterior lumbar spine, and use of nonautologous bone grafts.
Certainly, the most important variables retrieved from our trials will be antibiotic-related. Most author groups advocate a minimum length of parenteral antibiotic course of 2–4 weeks and a total duration up to 3 months [
15,
16] for SIs, although some groups recommend only 2 weeks of parental therapy [
17,
18], or even only 2–3 days [
19], without further compromising success. To cite examples, Clark and Shufflebarger [
20] treated delayed infections with surgery and 48–72 h of parenteral antibiotics followed by 10 days of targeted oral antibiotics. All infections were eradicated. Likewise, Richards and Emara [
21] prescribed systemic antimicrobials only for 3 weeks, administered 2–5 days parenterally, followed by a 7 to 14 day-course of oral treatment.
In the entire field of orthopedic infections, there are no formal scientific data proving the benefit of a systemic antibiotic therapy beyond 6 weeks compared with 4–6 weeks or even less. Exceptions are by nature expert opinions in previous book chapters or past publications without their own database analyses or the therapy of special microorganisms requiring long-lasting antibiotic therapies such as mycobacteria [
22],
Nocardia spp. [
23], and
Actinomyces or fungi [
24]. To cite recent and our own examples of investigations regarding the overall antibiotic duration, sacral osteomyelitis [
25], long-bone osteomyelitis [
10], fracture device-related infections [
12], spondylodiscitis [
25], prosthetic joint infections [
13], diabetic foot osteomyelitis [
26,
27], and many more failed to enhance remission rates if antibiotics were prolonged beyond 4–6 weeks, even in the presence of an infected implant. These emerging and relatively short durations are equally acknowledged by international consensus meetings [
28] of surgeons and infectious disease physicians who treat these infections and perform research on them.
There are also studies with less than 6 weeks of total antimicrobial therapy, especially in the pediatric literature on hematogenous osteomyelitis. In this particular setting, a 3-week antibiotic course appears to be sufficient, as highlighted by many authors [
29‐
32]. Among adults, 38 case series with antibiotic treatment durations of 3–4 weeks, including 5 to 36 patients each, revealed cure rates of approximately 80% according to a review published in 2005 [
33].
A second issue is the distinction between intravenous and oral antibiotic administration, at least initially. Current textbooks recommend the parenteral route for at least the first 2 weeks for all osteoarticular infections [
1,
34‐
36], but this recommendation is not evidence-based either. There are no predictive clinical markers that would justify prolonged initial intravenous administration. In addition, up to one-third of patients with chronic bone and implant infections may experience antibiotic-related or catheter-related problems during parenteral treatment [
36]. For economic reasons as well as patient and nurse comfort, parenteral administration should be kept to a minimum [
37]. Good bone penetration during parenteral and oral administration has been proven in several reports [
38‐
40], and data suggest that an early switch to oral antibiotics is as effective as prolonged parenteral regimens [
41].
A Cochrane review investigated five trials comparing oral vs. parenteral antibiotics in osteomyelitis. There was no statistically significant difference between the two groups in the remission rate 12 months or more after treatment [
42]. Glassman et al. successfully treated two patients with SIs from the start with oral ciprofloxacin, an antibiotic with excellent oral bioavailability and bone penetration [
43]. Even in cases of diabetic foot osteomyelitis, a frequent disease with a hallmark of vascular insufficiency and tissue ischemia, there are no data indicating the superiority of any particular route of delivery of systemic antibiotics [
44]. Byren et al. demonstrated that an intravenous course of antibiotics for over 4 weeks did not enhance cure for the treatment of arthroplasty infections [
45]. Zimmerli et al. summarized observational studies that showed the same failure rates of arthroplasty infection treatment despite a prolonged period (4–6 weeks) of intravenous treatment [
46]. For the treatment of bone infections, there are some antibiotics that have already been proven to be effective in oral form. Quinolones, rifampicin, co-trimoxazole, tetracycline, or clindamycin have such a good and sufficient oral bioavailability [
47].
Our future patient population will comprise all comorbidities and chronic immune suppressions. For example, we expect 20–25% of patients will have diabetes [
48] in our center, along with other immune suppressions such as cancer, advanced cirrhosis, and steroid medication. While immune suppression (especially diabetes mellitus) is an acknowledged independent risk associated with healthcare-associated surgical site infections [
49], its influence on remission during therapy for SIs is unknown. Indeed, all current therapeutic concepts for osteoarticular infections in general do not rely on the presence or absence of immune suppression [
1,
10,
12,
25], suggesting that surgical debridement and long antibiotic administration overcome eventual shortcomings of patients’ immunity. Although our SASI trials do not target the association of immune suppression with SI outcomes, we will see if immune suppression tends to decrease remission when we shorten the antibiotic duration.
Finally, our RCT will also give insight into the nutritional status of patients with SI. Current literature is divided between experts advocating a causal relationship between malnutrition and occurrence of surgical site infections in orthopedic surgery and others who have retrospectively investigated this relationship and mostly found no associations [
50]. Both factions know even less about the associations and the dynamics of nutritional status in already-infected orthopedic spine patients and the association of these alterations with remission, functional outcomes, and underlying immune suppression, let alone the question of the benefits of nutritional interventions during the combined surgical, physiotherapeutic, and antibiotic treatment [
51]. This will be
terra nova that we embed into our trials.
We do not expect major difficulties in performing our studies. Despite two prospective randomized designs (for SI with and without implants) and only 236 different episodes anticipated, patients’ voluntary participation might be low. Likewise, patients who continue to be treated outside of our center may be lost to follow-up or may have their treatment changed because the follow-up physicians do not agree. However, our center is the largest public hospital for surgical SIs in the region, and it is a university spine center, so this is unlikely to be a major bias. Last, and formally, our study participants will benefit from an initializing surgical debridement of infections. Hence, our results will not be valid for the conservative treatment of SI, which must not be confounded.
Acknowledgements
We are indebted to all teams of Balgrist University Hospital and Balgrist Campus for support, to the Zentrallabor Zürich (ZLZ) for laboratory analyses (chemistry and hematology), and to the Institute of Medical Microbiology, University of Zurich, for clinical bacterial analyses. We especially thank our nutrition specialists, Annette Seiler-Bänziger, Margrit Sahli, and Maja Kuhn, for their invaluable support and to Dario Frustaci for biobanking. This work will be supported by the Swiss Center for Musculoskeletal biobanking (SCMB), Balgrist Campus AG, Zurich, Switzerland.
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