In light of the debate regarding the appropriate duration of antibiotic treatment for pyogenic spondylodiscitis after surgical intervention, this study tried to evaluate the outcomes and the risk factors for recurrence and to determine the appropriate duration of postoperative parenteral antibiotic treatment. We found that positive blood culture and paraspinal abscess formation were the two independent risk factors for treatment failure that could be used to guide the implementation of parenteral antibiotic therapy after surgical intervention. Among the low-risk patients, the recurrence rates were similar in both the long-term and short-term subgroups. However, significantly increasing recurrent rates were observed in high-risk patients who received short-term intravenous antibiotic treatment. Therefore, our findings may assist in establishing the appropriate duration of parenteral antibiotic treatment after surgical intervention during admission (Fig. 4). Patients with pyogenic spondylodiscitis with either positive blood culture or paraspinal abscess may require a long duration (> 3 weeks) of postoperative parenteral antibiotic treatment. Otherwise, a short duration (3 weeks) of postoperative parenteral antibiotic treatment may be sufficient.
Regarding the optimal duration of antibiotic treatment in the general population of patients with pyogenic spondylodiscitis, Berbari et al. [8] suggested a total duration of 6 weeks of parenteral or highly bioavailable oral antimicrobial therapy for most patients and 12 weeks of antimicrobial therapy for patients with Brucella species infection. A randomized, controlled trial by Bernard et al. [1] showed that antibiotic treatment could be shortened to a total of 6 weeks without increasing the risk of relapse, failure, and infection-related mortality. However, there is an overall lack of evidence-based data regarding the risk factors of infection relapse, which have the potential to guide decisions as to the appropriate duration of antibiotic treatment after surgical intervention.
Park et al. [20] conducted a retrospective study of 314 patients with microbiologically diagnosed pyogenic spondylodiscitis. This study reported three independent risk factors for recurrence: methicillin-resistant Staphylococcus aureus (MRSA) infection, undrained paravertebral/psoas abscesses, and end-stage renal disease (ESRD). According to these three independent risk factors for recurrence, all patients were classified as either low-risk or high-risk, similarly to our study. In both groups, there were significant decreasing trends for recurrence according to the total duration of antibiotic therapy. This study concluded that antibiotic therapy of long duration (≥8 weeks) should be given to patients at high risk of recurrence. For low-risk patients, a shorter duration (6–8 weeks) of pathogen-directed antibiotic therapy was deemed adequate. However, since surgical intervention was performed in only 153 (44.3%) patients in that study, it is difficult to draw conclusions regarding the appropriate duration of antibiotic treatment after surgical intervention since more than half of the cohort of patients did not undergo surgery. By comparison, our study is stronger and is more focused on the appropriate duration of antibiotic treatment after surgical intervention for pyogenic spondylodiscitis.
Recurrence rates have been reported to range from 0 to 32%, and recurrence usually occurs within 6 months to 1 year [2, 7, 13, 21, 22]. Due to variable definitions of recurrence and inclusion criteria, it is difficult to compare recurrence rates between different studies. In the current study, 26 (25.5%) cases experienced recurrence. The failure rate in our study is similar to the rates reported by Arnold et al. [23]. They indicated that treatment failure is most likely to happen within the first year and demonstrated risk factors for treatment failure including infections of the lumbar or sacral spine and prior incision and drainage. In a 10-year retrospective study, Roblot et al. [9] also proposed risk factors for relapse, which included the use of corticosteroids, rheumatoid arthritis, endocarditis, high C-reactive protein value, and a longer duration of parenteral antibiotic therapy. Due to the small number of relapses, multivariable analysis was not performed in their study. McHenry et al. reported that recurrent bacteremia, paravertebral abscesses, and chronically draining sinuses were the independent risk factors associated with relapse [21]. Notably, in our study, diabetes mellitus (DM), end-stage renal disease (ESRD), methicillin-resistant Staphylococcus aureus (MRSA) infection, and epidural abscess showed a trend for higher risk of recurrence but didn’t achieve statistical significance. This result might be partially attributable to the relatively low number of participants in our study. There should still be special consideration for patients with these factors in clinical practice.
Surgical debridement provides eradication of infectious tissues and adequate tissues for culture to determine the type of bacteria, which informs the choice of appropriate antibiotics for optimal infection control. In theory, this could shorten the duration of the antibiotic course and reduce immobilization-related complications [24, 25]. Although a wide spectrum of organisms has been related with pyogenic spondylodiscitis, S. aureus is the predominant organism, accounting for around half of the cases (range 20–84%) in the literature [2, 11, 21, 22, 26, 27]. Enterobacteriaceae, such as E. coli, Proteus, Klebsiella, and Enterobacter spp., have accounted for 7–33% of pyogenic spondylodiscitis cases [2, 21, 22, 26, 27]. In addition, streptococci, enterococci, and coagulase-negative staphylococci (CoNS) are also well-described organisms that account for 5–20% [2, 11, 21, 26, 27]. Anaerobic bacteria rarely cause spondylodiscitis and are associated with less than 4% of cases [2, 11, 21, 26]. The findings of our study were in accordance with these rates of causative organisms.
Since pyogenic spondylodiscitis can be treated with conservative treatment [28,29,30], patients often receive empiric antibiotic treatment before a definite culture result has been obtained. In the current study, 66 patients (64.7%) received parenteral antibiotic treatment prior to surgery. However, culture yield may be decreased by antibiotic use before biopsy or surgery [2]. Among the 25 culture-negative cases in the current study, 22 (88%) had received antibiotic therapy before surgery (p = 0.005), which showed that a negative culture result is significantly associated with preoperative antibiotic treatment.
Our study had some limitations. Due to the retrospective design of the study, some important clinical characteristics may not have been recorded and some patients were lost to follow-up, which may have introduced unrecognized bias. There was also a selection bias of patients by their treating physicians, since the duration of intravenous antibiotic treatment was decided according to clinical and biological response to treatment in this retrospective study. In addition, this study included patients with both microbiologically proven and culture-negative cases. Hence, the included cases were of clinically defined pyogenic spondylodiscitis, and not all were microbiologically diagnosed, which may have also introduced unrecognized bias. Another potential limitation may be that the use of oral antibiotics was not included in our study, because we wanted to emphasize hospitalized treatment courses; additionally, patient compliance with oral antibiotics in the outpatient clinic can be difficult to control.