Factors related to outcome of early and delayed prosthetic joint infections

Relationship between biofilm-forming microorganisms (BFM: Staphylococcus aureus and Pseudomonas aeruginosa) and DEFB1 gene variants on β-defensin levels in periprosthetic joint infection (PJI)

BACKGROUND

The purpose of this study was to investigate the relationship between biofilm-forming microorganisms (BFM) and DEFB1 gene variants on β-defensin levels in patients with periprosthetic joint infection (PJI) of Mexican origin.

METHODS AND RESULTS

One hundred and five clinical aspirates were obtained from patients with suspected PJI. After microbiologic culture, samples were classified as non-septic and septic; of the latter, only those positive for Staphylococcus aureus and Pseudomonas aeruginosa were selected. β-Defensin levels were quantified by ELISA, DNA was extracted from total leukocytes of the samples, and - 20G > A (rs11362) and - 44 C > G (rs1800972) variants were genotyped using TaqMan probes. Forty-one clinical aspirates were non-septic, 18 were positive for S. aureus and 18 were positive for P. aeruginosa. It was observed that β-defensin levels were higher in the P. aeruginosa group compared to S. aureus group (2339.0 pg/mL IQR = 1809.2 vs. 1821.3 pg/mL IQR = 1536.4) and non-septic group (2339.0 pg/mL IQR = 1809.2 vs. 1099.7 pg/mL IQR = 1744.5, P < 0.001). The CG genotype of the rs1800972 variant was associated with higher β-defensin levels compared to the CC genotype for both P. aeruginosa and S. aureus (1905.8 vs. 421.7 pg/mL, P = 0.004; and 1878.2 vs. 256.4 pg/mL, P = 0.006, respectively).

CONCLUSIONS

Our results show that β-defensin levels are significantly elevated in patients with BFM-associated PJI compared to those without infection. Furthermore, carriers of the CG genotype of the rs1800972 variant have an increased risk of PJI. Further research is needed to replicate these findings in a larger population.

Clinical outcomes of rifampicin combination therapy in implant-associated infections due to staphylococci and streptococci: A systematic review and meta-analysis

OBJECTIVES

Adjunctive rifampicin for implant-associated infections is controversial. This study investigated the clinical outcomes of rifampicin combination therapy compared with monotherapy in treating prosthetic joint infection (PJI) or prosthetic valve endocarditis (PVE) due to staphylococci and streptococci.

METHODS

A systematic search was performed from inception to 13 June 2022 in Embase, MEDLINE, Cochrane and Web of Science to investigate the clinical outcomes of rifampicin combination therapy compared with monotherapy in treating staphylococcal and streptococcal PJI or PVE. Randomised controlled trials (RCTs) and observational studies were included in the systematic review and meta-analysis.

RESULTS

Fourteen studies were included. A moderate quality of evidence was found in favour of rifampicin in patients with staphylococcal PJI who underwent a debridement, antibiotics and implant retention (DAIR) procedure [odds ratio = 2.49, 95% confidence interval (CI) 1.93-3.23]. Including the two RCTs only, adding rifampicin to the antibiotic regimen after DAIR was also in favour of rifampicin, but this was not statistically significant (risk ratio = 1.27, 95% CI 0.79-2.04; n = 126). Pooling data for patients with staphylococcal PJI who underwent a two-stage procedure showed that adding rifampicin was not associated with therapeutic success. Limited evidence was found for the use of rifampicin for PVE caused by staphylococci.

CONCLUSIONS

Adding rifampicin in the treatment of staphylococcal PJI treated by DAIR clearly increased the likelihood for therapeutic success. The clinical benefit of adjunctive rifampicin in the treatment of other staphylococci and streptococci implant-associated infections is still unclear.

Promising applications of D-amino acids in periprosthetic joint infection

Due to the rise in our aging population, a disproportionate demand for total joint arthroplasty (TJA) in the elderly is forecast. Periprosthetic joint infection (PJI) represents one of the most challenging complications that can occur following TJA, and as the number of primary and revision TJAs continues to rise, an increasing PJI burden is projected. Despite advances in operating room sterility, antiseptic protocols, and surgical techniques, approaches to prevent and treat PJI remain difficult, primarily due to the formation of microbial biofilms. This difficulty motivates researchers to continue searching for an effective antimicrobial strategy. The dextrorotatory-isoforms of amino acids (D-AAs) are essential components of peptidoglycan within the bacterial cell wall, providing strength and structural integrity in a diverse range of species. Among many tasks, D-AAs regulate cell morphology, spore germination, and bacterial survival, evasion, subversion, and adhesion in the host immune system. When administered exogenously, accumulating data have demonstrated that D-AAs play a pivotal role against bacterial adhesion to abiotic surfaces and subsequent biofilm formation; furthermore, D-AAs have substantial efficacy in promoting biofilm disassembly. This presents D-AAs as promising and novel targets for future therapeutic approaches. Despite their emerging antibacterial efficacy, their role in disrupting PJI biofilm formation, the disassembly of established TJA biofilm, and the host bone tissue response remains largely unexplored. This review aims to examine the role of D-AAs in the context of TJAs. Data to date suggest that D-AA bioengineering may serve as a promising future strategy in the prevention and treatment of PJI.

Comparison of dynamic and static spacers for the treatment of infections following total knee replacement: a systematic review and meta-analysis

Background

Revision surgery is the most common treatment for patients who develop infection after total knee arthroplasty (TKA). Two types of spacers are often used in revision surgery: dynamic spacers and static spacers. The comparative efficacy of these two types of spacers on knee prosthesis infections is not well established. Therefore, we carried out a systematic evaluation and meta-analysis with the aim of comparing the difference in efficacy between dynamic and static spacers.

Methods

We conducted the literature search in PubMed, Web of Science, Cochrane Library, and Embase databases. The articles searched were clinical study comparing the difference in efficacy between dynamic spacers and static spacers for the treatment of prosthetic infections occurring after total knee arthroplasty.

Results

We conducted a literature search and screening based on the principles of PICOS. Ultimately, 14 relevant clinical studies were included in our current study. We use infection control rate as the primary evaluation indicator. The KSS knee scores (KSSs), KSS functional scores, bone loss and range of motion (ROM) are secondary indicators of evaluation. Thirteen of these included studies reported the infection control rates, with no significant difference between dynamic and static shims (RR: 1.03; 95% Cl 0.98, 1.09; P = 0.179 > 0.05). The KSSs were reported in 10 articles (RR: 5.98; 95% CI 0.52, 11.43; P = 0.032 < 0.05). Six articles reported the KSS functional scores (RR: 13.90; 95% CI 4.95, 22.85; P = 0.02 < 0.05). Twelve articles reported the ROM (RR: 17.23. 95% CI 10.18, 24.27; P < 0.0001). Six articles reported the bone loss (RR: 2.04; 95% CI 1.11, 3.77; P = 0.022 < 0.05).

Conclusion

Current evidence demonstrates that dynamic spacers are comparable to static spacers in controlling prosthetic joint infection. In terms of improving the functional prognosis of the knee joint, dynamic spacers are more effective than static spacers.

Debridement and implant retention in acute hematogenous periprosthetic joint infection after knee arthroplasty: a systematic review

Debridement, antibiotic, and implant retention (DAIR) can be used as a first surgical procedure for acute infections in patients who have well-fixed components. However, its use in hematogenous or late acute infections is still debated. This systematic review of literature aims to clarify the effectiveness of DAIR procedure in the treatment of hematogenous periprosthetic knee infections. DAIR is an effective way to treat acute hematogenous PJIs of the knee and reaches its best efficacy when performed within one week from the onset of symptoms, modular components are exchanged, and a pathogen-oriented antibiotic therapy can be set. It is safe, economic, and effective technique, but has to be performed in a very narrow temporal window.

Delayed Rifampin Administration in the Antibiotic Treatment of Periprosthetic Joint Infections Significantly Reduces the Emergence of Rifampin Resistance

Rifampin is one of the most important biofilm-active antibiotics in the treatment of periprosthetic joint infection (PJI), and antibiotic regimens not involving rifampin were shown to have higher failure rates. Therefore, an emerging rifampin resistance can have a devastating effect on the outcome of PJI. The aim of this study was to compare the incidence of rifampin resistance between two groups of patients with a PJI treated with antibiotic regimens involving either immediate or delayed additional rifampin administration and to evaluate the effect of this resistance on the outcome. In this retrospective analysis of routinely collected data, all patients who presented with an acute/chronic PJI between 2018 and 2020 were recorded in the context of a single-center comparative cohort study. Two groups were formed: Group 1 included 25 patients with a PJI presenting in 2018-2019. These patients received additional rifampin only after pathogen detection in the intraoperative specimens. Group 2 included 37 patients presenting in 2019-2020. These patients were treated directly postoperatively with an empiric antibiotic therapy including rifampin. In all, 62 patients (32 females) with a mean age of 68 years and 322 operations were included. We found a rifampin-resistant organism in 16% of cases. Rifampin resistance increased significantly from 12% in Group 1 to 19% in Group 2 (p < 0.05). The treatment failure rate was 16% in Group 1 and 16.2% in Group 2 (p = 0.83). The most commonly isolated rifampin-resistant pathogen was Staphylococcus epidermidis (86%) (p < 0.05). The present study shows a significant association between the immediate start of rifampin after surgical revision in the treatment of PJI and the emergence of rifampin resistance, however with no significant effect on outcome.

Synovial Cell Count Before Reimplantation Can Predict the Outcome of Patients with Periprosthetic Knee Infections Undergoing Two-stage Exchange

BACKGROUND

Although synovial fluid can be used to diagnose periprosthetic joint infections (PJI) effectively, only the cutoff values adopted at the time of PJI diagnosis have been standardized, and few data are currently available about effectiveness of synovial fluid examination before definitive reimplantation.

QUESTIONS/PURPOSES

We asked: (1) What are the most appropriate thresholds for synovial fluid leukocyte counts (WBC) and neutrophil percentage (PMN percentage) in a patient group undergoing definitive reimplantation after an uninterrupted course of antibiotic therapy for chronic PJI? (2) What is the predictive value of our synovial WBC and PMN percentage threshold compared with previously proposed thresholds?

METHODS

In all, 101 patients with PJI were evaluated for inclusion from January 2016 to December 2018. Nineteen percent (19 of 101) of patients were excluded because of the presence of a chronic inflammatory disease, acute/late hematogenous infection, low amount of synovial fluid for laboratory investigations or infection persistence after spacer placement, and adequate antibiotic therapy. Finally, 81% (82 of 101) of patients with a median (range) age of 74 years (48 to 92) undergoing two-stage revision for chronic TKA infection, who were followed up at our institution for a period 96 weeks or more, were included in this study. The patients did not discontinue antibiotic treatment before reimplantation and were treated for 15 days after reimplantation if intraoperative cultures were negative. No patient remained on suppressive treatment after reimplantation. Synovial fluid was aspirated aseptically with a knee spacer in place to evaluate the cell counts before reimplantation. Thirteen percent (11 of 82) of patients had persistent or recurrent infection, defined as continually elevated erythrocyte sedimentation rate or C-reactive protein levels coupled with local signs and symptoms or positive cultures. The synovial fluid WBC counts and PMN percentage from the 11 patients with persistent or recurrent PJI were compared with the 71 patients who were believed to be free of PJI. Receiver operating characteristic (ROC) curve analyses assessed the predictive value of the parameters, and the areas under the curves (AUCs) were evaluated. The sensitivities, specificities, and positive and negative predictive values were determined for the WBC count and PMN percentage. Patients with persistent or recurrent infection had higher median WBC counts (471 cells/µL versus 1344 cells/µL; p < 0.001) and PMN percentage (36% versus 61%; p < 0.001) than did patients believed to be free of PJI.

RESULTS

ROC curve analysis identified the best threshold values to be a WBC count of 934 cells/µL or more (sensitivity 0.82 [95% CI 0.71 to 0.89], specificity 0.82 [95% CI 0.71 to 0.89]) as well as a PMN percentage of at least 52% (sensitivity 0.82 [95% CI 0.71 to 0.89] and specificity 0.78 [95% CI 0.67 to 0.86]. We found no difference between the AUCs for the WBC count and the PMN percentage (0.87 [95% CI 0.79 to 0.96] versus 0.84 [95% CI 0.73 to 0.95]. Comparing the sensitivities and specificities of the synovial fluid WBC count and PMN percentage proposed by other authors, we find that a PMN percentage more than 52% showed better predictive value than previously reported.

CONCLUSION

Based on our findings, we believe that patients with WBC counts of at least 934 and PMN percentage of 52% or more should not undergo reimplantation but rather a repeat debridement, as their risk of persistent or recurrent PJI appears prohibitively high. The accuracy of the proposed cutoffs is better than previously reported.

LEVEL OF EVIDENCE

Level III, diagnostic study.

Outcome of Debridement, Antibiotics, and Implant Retention for Staphylococcal Hip and Knee Prosthetic Joint Infections, Focused on Rifampicin Use: A Systematic Review and Meta-Analysis

The treatment of staphylococcal prosthetic joint infection (PJI) with debridement, antibiotics, and retention of the implant (DAIR) often results in failure. An important evidence gap concerns the treatment with rifampicin for PJI. A systematic review and meta-analysis were conducted to assess the outcome of staphylococcal hip and/or knee PJI after DAIR, focused on the role of rifampicin. Studies published until September 2, 2020 were included. Success rates were stratified for type of joint and type of micro-organism. Sixty-four studies were included. The pooled risk ratio for rifampicin effectiveness was 1.10 (95% confidence interval, 1.00-1.22). The pooled success rate was 69% for Staphylococcus aureus hip PJI, 54% for S aureus knee PJI, 83% for coagulase-negative staphylococci (CNS) hip PJI, and 73% for CNS knee PJI. Success rates for MRSA PJI (58%) were similar to MSSA PJI (60%). The meta-analysis indicates that rifampicin may only prevent a small fraction of all treatment failures.

Safety and Tolerability of Fluoroquinolones in Patients with Staphylococcal Periprosthetic Joint Infections

BACKGROUND

Fluoroquinolones (FQs) are known to be accompanied by significant risks. However, the incidence of adverse events (ADE) resulting in unplanned drug discontinuation when used for periprosthetic joint infections (PJI) is currently unknown.

METHODS

This study included 156 patients over the age of 18 treated for staphylococcal PJI with debridement, antibiotics, and implant retention (DAIR), between January 1, 2007 and November 21, 2019. Of the 156 patients, 64 had total hip arthroplasty (THA) and 92 had total knee arthroplasty (TKA) infections. The primary outcome was rate of unplanned drug discontinuation. Secondary outcomes included incidence of severe ADE, unplanned rifamycin discontinuation, mean time to unplanned regimen discontinuation, and all-cause mortality.

RESULTS

Overall, unplanned drug discontinuation occurred in 35.6% of patients in the FQ group and 3% of patients in the non-FQ group. The rate of unplanned discontinuation of FQ regimens as compared to non-FQ regimens was 27.5% vs 4.2% (p=0.021) in THA infections and 42% vs 2.4% (p<0.001) in TKA infections. There was no significant difference in severe ADEs between FQ and non-FQ regimens in both THA and TKA infections. The overall rate of non-severe ADEs in FQ compared to non-FQ regimens was 43.3% vs 6.1% (p<0.001). FQs were associated with tendinopathy, myalgia, arthralgia, and nausea.

CONCLUSIONS

A significantly higher rate of unplanned drug discontinuation was associated with FQ as compared to non-FQ regimens. This provides a real-world view of the implications of FQ related adverse events on unplanned discontinuation when used in prolonged durations for the management of staphylococcal PJIs.

Noninvasive diagnostic of periprosthetic joint infection by urinary peptide markers: A preliminary study

Previous immunohistochemical analyses revealed altered protein expression in the periprosthetic membranes of patients with periprosthetic joint infection (PJI). Proteins are degraded to peptides that may pass the blood-kidney barrier depending on their size. The aim of this study was to evaluate if PJI can be diagnosed based on the urinary peptide excretion pattern. Thirty patients undergoing removal of their hip or knee prostheses due to septic or aseptic loosening were enrolled. Specimen sampling was performed according to the MusculoSkeletal Infection Society criteria. A urinary sample was analyzed before surgery using capillary electrophoresis coupled with mass spectrometry. Peptides with differential urinary excretion between groups were used to establish a multimarker model. A total of 137 peptides were differentially excreted between the septic and aseptic groups. The majority of identified peptide markers were fragments of structural extracellular matrix proteins, potentially due to their origin from the periprosthetic membrane. A marker model with 83 peptides achieved the best diagnostic performance for diagnosing PJI with a sensitivity of 95%, a specificity of 90%, and an area under the curve of 0.96. The altered protein expression pattern in the periprosthetic membrane of PJI is most likely reflected in excreted urinary peptides. Thus, the diagnosis of PJI by urinary peptide markers seems to be a reasonable approach.

Pseudomonas aeruginosa Implant-Associated Bone and Joint Infections: Experience in a Regional Reference Center in France

Background:P. aeruginosa implant-associated bone and joint infections (BJI) is considered to be one of the most difficult to treat BJI. The data focusing specifically on this pathogen are sparse, and it seems difficult to extrapolate the results obtained with Enterobacteriaceae.

Methods: We performed a retrospective observation study of all P. aeruginosa implant-associated BJI diagnosed at our institution from 2011 to 2018. We defined failure as any type of relapse, including persistence of the same P. aeruginosa, superinfection by another organism(s) or any other cause of relapse such as the need for a subsequent surgery. Nonparametric statistical methods were used to compare the study groups and Kaplan-Meier curves and multivariate Cox analysis and were used to detect determinants associated with treatment failure.

Results: A total of 90 patients (62% men, median age 60 years IQR 47–72) including 30 (33%) prosthetic-joint infections and 60 (66%) other implant-associated BJIs were studied. Most of them were acute (62%). During the prolonged follow-up, (median 20 months; IQR 9–37), 23 patients (26%) experienced treatment failure. Optimal surgical treatment (DAIR for acute forms, explantation, 1-stage or 2-stage exchange for others) was significantly associated with a higher success rate in the univariate analysis (p = 0.003). Sixty-four (71%) patients received effective initial treatment against P. aeruginosa administered and 81 of them (90%) did for at least 3 weeks: both these parameters correlated with a higher success rate. In the multivariate Cox-analysis optimal surgical treatment, IV effective treatment of at least 3 weeks and treatment with ciprofloxacin for at least 3 months proved to be independently associated to a better outcome in patients with P. aeruginosa implant-associated BJI.

Conclusion:P. aeruginosa implant-associated BJI is one of the most difficult-to-treat BJI, with a strong impact on the prognosis of the surgical strategy. An effective initial IV antibiotic treatment for at least 3 weeks seems to be required, followed by oral ciprofloxacin for a total duration of 3 months.

When antibiotics fail: a clinical and microbiological perspective on antibiotic tolerance and persistence of Staphylococcus aureus

Staphylococcus aureus is a major human pathogen causing a vast array of infections with significant mortality. Its versatile physiology enables it to adapt to various environments. Specific physiological changes are thought to underlie the frequent failure of antimicrobial therapy despite susceptibility in standard microbiological assays. Bacteria capable of surviving high antibiotic concentrations despite having a genetically susceptible background are described as 'antibiotic tolerant'. In this review, we put current knowledge on environmental triggers and molecular mechanisms of increased antibiotic survival of S. aureus into its clinical context. We discuss animal and clinical evidence of its significance and outline strategies to overcome infections with antibiotic-tolerant S. aureus.

Epidemiology and microbiology of prosthetic joint infections: a nine-year, single-center experience in Pavia, Northern Italy

BACKGROUND

Prosthetic joint infections (PJIs) are a growing matter of concern due to their economic and social burden on health systems. In Italy, surgical data on PJIs are available in a national registry, but microbiological data are still scarce.

MATERIALS AND METHODS

We performed a retrospective study at a single center with records of patients treated for primary PJIs of knee or hip from January 1, 2011, to May 30, 2018. Patients with infections of osteosynthesis means and external devices were excluded, as well as PJI recurrences and polytrauma patients. Infections were diagnosed according to IDSA and MSIS criteria. We collected data on demographics, risk factors and microbiology. All patients seen at our center undergo blood cultures and synovial fluid cultures, periarticular biopsy and prosthesis sonication by Bactosonic^®. This was used only after 2014. Bacterial identification is achieved by MALDI-TOF, PHOENIX 100 and standard methods. Chi-square or Fisher tests were used to test statistical differences in proportions.

RESULTS

Fifty-one patients matched our inclusion criteria. Of these, 16 (31.4%) were enrolled before 2014. The median age was 68.5 (range 22-88). The most common risk factors were obesity (34%), diabetes (21%) and chronic kidney disease (14%). Seventeen patients were diagnosed with a culture-negative PJIs (33.3%). Staphylococcus aureus was the most commonly isolated pathogen (14/51, 27.5%), followed by coagulase-negative staphylococci (7/51, 13.7%). Methicillin-resistant S. aureus rate was 28.6%. The rate of culture-negative PJIs dropped from 56 to 22% after 2014, with a significant difference between the two time periods (p = 0.016).

CONCLUSIONS

The introduction of sonication dramatically increased our diagnostic accuracy. Our microbiological data are in line with those from other studies conducted in Italy.

Multidrug-resistant and extensively drug-resistant Gram-negative prosthetic joint infections: Role of surgery and impact of colistin administration

Factors influencing treatment outcome of patients with Gram-negative bacterial (GNB) multidrug-resistant (MDR) and extensively drug-resistant (XDR) prosthetic joint infection (PJIs) were analysed. Data were collected (2000-2015) by 18 centres. Treatment success was analysed by surgery type for PJI, resistance (MDR/XDR) and antimicrobials (colistin/non-colistin) using logistic regression and survival analyses. A total of 131 patients (mean age 73.0 years, 35.9% male, 58.8% with co-morbidities) with MDR (n = 108) or XDR (n = 23) GNB PJI were assessed. The most common pathogens were Escherichia coli (33.6%), Pseudomonas aeruginosa (25.2%), Klebsiella pneumoniae (21.4%) and Enterobacter cloacae (17.6%). Pseudomonas aeruginosa predominated in XDR cases. Isolates were carbapenem-resistant (n = 12), fluoroquinolone-resistant (n = 63) and ESBL-producers (n = 94). Treatment outcome was worse in XDR versus MDR cases (P = 0.018). Success rates did not differ for colistin versus non-colistin in XDR cases (P = 0.657), but colistin was less successful in MDR cases (P = 0.018). Debridement, antibiotics and implant retention (DAIR) (n = 67) was associated with higher failure rates versus non-DAIR (n = 64) (OR = 3.57, 95% CI 1.68-7.58; P < 0.001). Superiority of non-DAIR was confirmed by Kaplan-Meir analysis (HR = 0.36, 95% CI 0.20-0.67) and remained unchangeable by time of infection (early/late), antimicrobial resistance (MDR/XDR) and antimicrobials (colistin/non-colistin) (Breslow-Day, P = 0.737). DAIR is associated with higher failure rates even in early MDR/XDR GNB PJIs versus implant removal. Colistin should be preserved for XDR cases as it is detrimental in MDR infections.

Role of Rifampin against Staphylococcal Biofilm Infections In Vitro, in Animal Models, and in Orthopedic-Device-Related Infections

Rifampin has been used as an agent in combination therapy in orthopedic device-related infections (ODRI) for almost three decades. The aim of this review is to provide data regarding the role of rifampin against biofilm infection in vitro, in animal models, and in clinical ODRI. Available data are gathered in order to present the rational use of rifampin combinations in patients with periprosthetic joint infection (PJI). The role of rifampin is well defined in patients with PJI and is indicated in those who fulfill the Infectious Diseases Society of America criteria for debridement and implant retention or one-stage exchange. It should be used with care because of the danger of rapid emergence of resistance. Potential drug interactions should be considered.

High performance of α-defensin lateral flow assay (Synovasure) in the diagnosis of chronic knee prosthetic infections

PURPOSE

This prospective study was undertaken to evaluate the diagnostic accuracy of the Synovasure™ α-defensin lateral flow assay to detect or exclude infection and to compare it to the sensitivity and specificity of other diagnostic criteria according to the International Consensus Group on Periprosthetic Joint Infection (PJI).

METHODS

All patients who have undergone revision total knee arthroplasty (TKA) from September 2015 to July 2016 were included: 16 chronic (more than 3 months after performing arthroplasty) infections and 35 aseptic joints were identified. The diagnostic performance of single test was assessed by receiver operating characteristic (ROC) curve analyses. The sensitivity and specificity were calculated for each of the cut-off values and the area under the curve (AUC) was also calculated.

RESULTS

The median synovial fluid (SF) leukocyte count, as well as the neutrophil percentage, was significantly higher in patients with PJI than in those with aseptic failure (p < 0.001). The sensitivity of α-defensin was 87.5% (95%; CI 74.6-94.7), the specificity was 97.1% (95% CI 86.9-99.7), the positive predictive value 93.3% (95% CI 81.8-98.1), and negative predictive value was 94.4% (95% CI 83.2-98.6). The results in terms of sensitivity and negative predictive value were greater than those of the other tests (cultures, synovial cell count, erythrocyte sedimentation rate, and C-reactive protein). The diagnostic accuracy of α-defensin, with an area under the curve of 0.92, was found to be higher than all the minor criteria for PJI.

CONCLUSIONS

In this study, the α-defensin lateral flow test was found to have the highest performance of all tests studied to identify PJI. Synovasure™ holds the potential to be included in the daily clinical practice.

LEVEL OF EVIDENCE

Level I diagnostic study.

Simple Sample Preparation Method for Direct Microbial Identification and Susceptibility Testing From Positive Blood Cultures

Rapid identification and determination of the antibiotic susceptibility profiles of the infectious agents in patients with bloodstream infections are critical steps in choosing an effective targeted antibiotic for treatment. However, there has been minimal effort focused on developing combined methods for the simultaneous direct identification and antibiotic susceptibility determination of bacteria in positive blood cultures. In this study, we constructed a lysis-centrifugation-wash procedure to prepare a bacterial pellet from positive blood cultures, which can be used directly for identification by matrix-assisted laser desorption/ionization-time-of-flight mass spectrometry (MALDI-TOF MS) and antibiotic susceptibility testing by the Vitek 2 system. The method was evaluated using a total of 129 clinical bacteria-positive blood cultures. The whole sample preparation process could be completed in <15 min. The correct rate of direct MALDI-TOF MS identification was 96.49% for gram-negative bacteria and 97.22% for gram-positive bacteria. Vitek 2 antimicrobial susceptibility testing of gram-negative bacteria showed an agreement rate of antimicrobial categories of 96.89% with a minor error, major error, and very major error rate of 2.63, 0.24, and 0.24%, respectively. Category agreement of antimicrobials against gram-positive bacteria was 92.81%, with a minor error, major error, and very major error rate of 4.51, 1.22, and 1.46%, respectively. These results indicated that our direct antibiotic susceptibility analysis method worked well compared to the conventional culture-dependent laboratory method. Overall, this fast, easy, and accurate method can facilitate the direct identification and antibiotic susceptibility testing of bacteria in positive blood cultures.

Knee Septic Arthritis after Arthroscopy: Incidence, Risk Factors, Functional Outcome, and Infection Eradication Rate

Purpose  Septic knee arthritis following arthroscopy is a rare but dreaded complication. Definition and management of knee deep infections are quite discussed in literature. In this review, literature regarding infections after knee arthroscopy is analyzed highlighting the incidence, causative bacteria, risk factors as well as clinical outcomes.

Methods  We performed a review of the literature matching the following key words: “septic arthritis” OR “infection” AND “arthroscopy” AND “knee.” Knee arthroscopic procedures, such as debridement, meniscectomy, meniscus repair, synovectomy, microfracture, and lateral release, were considered. Complex procedures, such as ligament reconstruction, fractures, or complex cartilage repair techniques, were not included.

Results  Thirteen studies were included in this review. Incidence of infection ranged from 0.009 to 1.1% in patients undergoing simple arthroscopic procedures. Staphylococci are the most commonly isolated organisms from postarthroscopy infection. Use of intraoperative intra-articular steroids, smoking, obesity, male sex, diabetes, number of procedures performed during surgery, time of surgery, and tourniquet time of more than 60 minutes have been certified as risk factors for knee infection.

Conclusion  Postarthroscopy septic arthritis of the knee causes significant morbidity, usually requiring readmission to the hospital, at least one additional operation, and prolonged antibiotic therapy, both intravenous and oral. Prompt diagnosis and treatment are associated with a high success rate.

Level of Evidence  Level IV, systematic review of I-IV studies.

Diagnosis and management of skin and soft-tissue infections (SSTI). A literature review and consensus statement: an update

Skin and soft-tissue infections (SSTIs) are among the most common bacterial infections, posing considerable diagnostic and therapeutic challenges. Fourteen members of the Italian Society of Infectious Diseases, after a careful review of the most recent literature using Medline database and their own clinical experience, updated a previous paper published in 2011 by preparing a draught manuscript of the statements. The manuscript was successively reviewed by all members and ultimately re-formulated the present manuscript during a full day consensus meeting. The microbiological and clinical aspects together with diagnostic features were considered for necrotizing and not necrotizing SSTIs in the light of the most recent guidelines and evidences published in the last five years. The antimicrobial therapy was considered as well - both empirical and targeted to methicillin-resistant Staphylococcus aureus and/or other pathogens, also taking into account the epidemiological and bacterial resistance data and the availability of new antibacterial agents.

Distribution characteristics of Staphylococcus spp. in different phases of periprosthetic joint infection: A review

Periprosthetic joint infection (PJI) is a devastating condition and Staphylococcus spp. are the predominant pathogens responsible, particularly coagulase-negative staphylococci (CoNS) and Staphylococcus aureus. The aim of the present systematic review was to evaluate the distribution characteristics of specific Staphylococcus spp. in different PJI phases, reveal the effect of pathogens' feature on their distribution and suggest recommendations for antibiotic treatment of Staphylococcal PJI. The present systematic review was performed using PubMed and EMBASE databases with the aim to identify existing literature that presented the spectrum of Staphylococcus spp. that occur in PJI. Once inclusion and exclusion criteria were applied, 20 cohort studies involving 3,344 cases in 3,199 patients were included. The predominant pathogen involved in PJI was indicated to be CoNS (31.2%), followed by S. aureus (28.8%). This trend was more apparent in hip replacement procedures. In addition, almost equal proportions of CoNS and S. aureus (28.6 and 30.0%, respectively) were indicated in the delayed phase. CoNS (36.6%) were the predominant identified organism in the early phase, whereas S. aureus (38.3%) occurred primarily in the late phase. In PJI caused by S. aureus, the number of cases of methicillin-sensitive Staphylococcus aureus (MSSA) was ~2.5-fold greater than that of methicillin-resistant Staphylococcus aureus (MRSA). MRSA occurred predominantly in the early phase, whereas MSSA was largely observed in the delayed and late phases. With regards to antibiotic treatment, the feature of various pathogens and the phases of PJI were the primary considerations. The present review provides useful information for clinical practice and scientific research of PJI.

Clinical and microbiological outcomes in haematogenous spondylodiscitis treated conservatively

INTRODUCTION

Spondylodiscitis refers to infections of the intervertebral disc and the adjacent vertebral body. Although it is still considered a rare condition, its rate is projected to increase. Mortality rate is considered to be low, but an estimated one third of the survivors experience residual disabilities. Literature shows that uncomplicated spondylodiscitis can be adequately treated by early antibiotic therapy and immobilization. The aim of the study is to evaluate the outcome of conservative treatment in patients with haematogenous spondylodiscitis.

MATERIALS AND METHODS

All patients with haematogenous spondylodiscitis observed in two orthopaedic centres were retrospectively considered. The medical records, radiologic imaging, bacteriology results, treatment, and complications of all patients were reviewed.

RESULTS

Thirty patients (median age 64 years, range 15-77, females 56.7%) were considered in the study, eight (26.7%) showed residual back pain at median follow-up of 117 weeks (range 104-189). A significant difference in SF-36 physical (P < 0.001), SF-36 mental function (P < 0.002), and Oswestry Disability Index (ODI) (P < 0.001) scores was observed among patients with residual local pain compared to the ones who had not. Methicillin-resistant Staphylococcus aureus (MRSA) infection and symptoms duration before the diagnosis were associated with an increased risk of persistent back pain and permanent disability. The most important negative determinants of SF-36 mental function were the age of patients (ρ = 0.36, P < 0.05), the duration of symptoms before the diagnosis (ρ = 0.44, P < 0.05) and MRSA infection (P = 0.006). Spondylodiscitis sustained by MRSA and the duration of symptoms before the diagnosis influenced negatively the physical status (P = 0.002) and ODI (ρ = 0.36, P < 0.05), respectively.

CONCLUSIONS

Conservative approaches are safe and effective for patients without complications. A delayed diagnosis and MRSA infections are related to poor clinical outcome among patients treated by conservative treatment; this must be carried out scrupulously with close patient monitoring.

Pseudomonas Prosthetic Joint Infections: A Review of 102 Episodes

Background: The outcome of patients with Pseudomonas prosthetic joint infection (PS PJI) has not been well studied. The aim of this retrospective cohort study was to assess the outcome of patients with Pseudomonas PJI and to review risk factors associated with failure of therapy. Methods: Between 1/1969 and 12/2012, 102 episodes of PS PJI in 91 patients were identified. Results: The mean age at the time of diagnosis was 67.4 years; forty three percent had knee involvement. Over 40 percent had either diabetes mellitus or a history of gastrointestinal or genitourinary surgery. Nearly half (48 out of 102 episodes) received aminoglycoside monotherapy, while 25% received an anti-pseudomonal cephalosporin. The 2-year cumulative survival free from failure was 69% (95% CI, 56%-82%). Patients treated with resection arthroplasty, two-stage exchange, and debridement with implant retention had a 2-year cumulative survival free from failure of 80% (95% CI, 66%-95%), 83% (95% CI, 60%-100%), and 26% (95% CI, 23%-29%) respectively (P=0.0001). Conclusions: PS PJI's are associated with a high failure rate. Patients treated with debridement and implant retention had a worse outcome.

Rapid Identification and Multiple Susceptibility Testing of Pathogens from Positive-Culture Sterile Body Fluids by a Combined MALDI-TOF Mass Spectrometry and Vitek Susceptibility System

Infections of the bloodstream, central nervous system, peritoneum, joints, and other sterile areas are associated with high morbidity and sequelae risk. Timely initiation of effective antimicrobial therapy is crucial to improving patient prognosis. However, standard final identification and antimicrobial susceptibility tests (ASTs) are reported 16–48 h after a positive alert. For a rapid, effective and low-cost diagnosis, we combined matrix-assisted laser desorption/ionization time of flight mass spectrometry with a Vitek AST system, and performed rapid microbial identification (RMI) and rapid multiple AST (RMAST) on non-duplicated positive body fluid cultures collected from a hospital in Shanghai, China. Sterile body fluid positive culture and blood positive culture caused by Gram negative (GN) or polymicrobial were applied to the MALDI–TOF measurement directly. When positive blood culture caused by Gram positive (GP) bacteria or yeasts, they were resuspended in 1 ml brain heart infusion for 2 or 4 h enrichment, respectively. Regardless of enrichment, the RMI (completed in 40 min per sample) accurately identified GN and GP bacteria (98.9 and 87.2%, respectively), fungi (75.7%), and anaerobes (94.7%). Dominant species in multiple cultures and bacteria that failed to grow on the routing plates were correctly identified in 81.2 and 100% of cases, respectively. The category agreements of RMAST results, determined in the presence of various antibiotics, were similarly to previous studies. The RMI and RMAST results not only reduce the turnaround time of the patient report by 18–36 h, but also indicate whether a patient's antibiotic treatment should be accelerated, ceased or de-escalated, and adjusted the essential drugs modification for an optimized therapy.