Use of broth cultures peri-operatively to optimise the microbiological diagnosis of musculoskeletal implant infections

Optimal concentration of ethylenediaminetetraacetic acid as an irrigation solution additive to reduce infection rates in rat models of contaminated wound

AIMS

In wound irrigation, 1 mM ethylenediaminetetraacetic acid (EDTA) is more efficacious than normal saline (NS) in removing bacteria from a contaminated wound. However, the optimal EDTA concentration remains unknown for different animal wound models.

METHODS

The cell toxicity of different concentrations of EDTA dissolved in NS (EDTA-NS) was assessed by Cell Counting Kit-8 (CCK-8). Various concentrations of EDTA-NS irrigation solution were compared in three female Sprague-Dawley rat models: 1) a skin defect; 2) a bone exposed; and 3) a wound with an intra-articular implant. All three models were contaminated with Staphylococcus aureus or Escherichia coli. EDTA was dissolved at a concentration of 0 (as control), 0.1, 0.5, 1, 2, 5, 10, 50, and 100 mM in sterile NS. Samples were collected from the wounds and cultured. The bacterial culture-positive rate (colony formation) and infection rate (pus formation) of each treatment group were compared after irrigation and debridement.

RESULTS

Cell viability intervened below 10 mM concentrations of EDTA-NS showed no cytotoxicity. Concentrations of 1, 2, and 5 mM EDTA-NS had lower rates of infection and positive cultures for S. aureus and E. coli compared with other concentrations in the skin defect model. For the bone exposed model, 0.5, 1, and 2 mM EDTA-NS had lower rates of infection and positive cultures. For intra-articular implant models 10 and 50 mM, EDTA-NS had the lowest rates of infection and positive cultures.

CONCLUSION

The concentrations of EDTA-NS below 10 mM are safe for irrigation. The optimal concentration of EDTA-NS varies by type of wound after experimental inoculation of three types of wound. Cite this article: Bone Joint Res 2021;10(1):68-76.

[Risk factors for multiple debridements of the patients with deep incisional surgical site infection after spinal surgery]

OBJECTIVE

To investigate the risk factors that contribute to multiple debridements in patients suffering from deep incisional surgical site infection after spinal surgery and advise medical personnel to pay special attention to these risk factors.

METHODS

We retrospectively enrolled 84 patients who got deep incisional surgical site infection after spinal surgery from Jan. 2012 to Dec. 2017. The infections occurred within 30 days after the surgery, and the identification met the criteria of deep incisional surgical site infection of Centers of Disease Control (CDC). Early debridement with first stage closure of the wound and a continuous inflow-outflow irrigation system was used, and reasonable antibiotics were chosen according to the bacterial culture results. During the treatment, the vital signs, clinical manifestations, blood test results, drainage fluid colour and bacterial culture results were acquired. If the infection failed to be controlled or relapsed, a second debridement was performed. Of the 84 cases, 60 undergwent single debridement which included 36 male cases and 24 female cases, and the age ranged from 36 to 77 years, with a mean of 57.2 years. Twenty four had multiple debridements (twice in 14 cases, three times in 6 cases, four times in 1 case, five times in 2 cases, six times in 1 cases) which included 17 male cases and 7 female cases, and the age ranged from 21 to 70 years, with a mean of 49.5 years. Risk factors that predispose patients to multiple debridements were identified using univariate analysis. Risk factors with P values less than 0.05 in univariate analysis were included together in a multivariate Logistic regression model using back-forward method.

RESULTS

Multiple debridements were performed in 28.6% of all cases. The hospital stay of multiple debridements group was (82.4±46.3) days compared with (40.4±31.5) days in single debridement group (P=0.018). Instrumentation was removed in 6 cases in multiple debridements group and 4 cases in single debridement group (P=0.049). Flap transplantation was performed in 7 cased in multiple debridements group while none in single debridement group (P < 0.001). Diabetes, primary operation duration longer than 3 hours, primary operation blood loss more than 400 mL, bacteriology examination results, distant site infection were significantly different between the two groups in univariate analysis. In multivariate analysis, primary operation duration longer than 3 hours (OR=3.60, 95%CI: 1.12-11.62), diabetes (OR=3.74, 95%CI: 1.06-13.22), methicillin-resistant Staphylococcus aureus (MRSA) infected (OR=16.87, 95%CI: 2.59-109.73) were the most important risk factors related to multiple debridements in the patients with deep incisional surgical site infection after spinal surgery.

CONCLUSION

Diabetes, primary operation duration more than 3 hours, MRSA infected are independent risk factors for multiple debridements in patients suffering from deep incisional surgical site infection after spinal surgery. Special caution and prophylaxis interventions are suggested for these factors.

Differences in Diagnostic Properties Between Standard and Enrichment Culture Techniques Used in Periprosthetic Joint Infections

BACKGROUND

Culture-negative infections can complicate the diagnosis and management of orthopedic infections, particularly periprosthetic joint infections (PJIs). This study aimed to identify differences in rate of detection of infection and organisms between cultured using standard and enriched methods.

METHODS

This retrospective, cross-sectional study evaluated PJI samples obtained between January 2013 and December 2017 at Yokohama City University Hospital. Samples were assessed using standard and enrichment culture techniques. White blood cell counts, C-reactive protein levels, type of microorganism (coagulase-positive or coagulase-negative), and methicillin-resistant Staphylococcus were investigated.

RESULTS

A total of 151 PJI samples were included in the analysis; of these, 68 (45.0%) were positive after standard culture while 83 (55.0%) were positive only after enrichment culture. The mean white blood cell counts and C-reactive protein levels were significantly lower in the enrichment culture group than in the standard culture group (P < .01). The rate of methicillin-resistant Staphylococcus and coagulase-negative Staphylococci was significantly higher in the enrichment culture group than in the standard culture group (P < .01).

CONCLUSION

The enrichment culture method has a higher rate of detection of infection than standard culture techniques and should, therefore, be considered when diagnosing orthopedic infections, particularly PJI.

Positive "Surprise" Broth Cultures in Nonunion Surgery Do Not Require Antibiotic Treatment

The objective of this study was to review the efficacy of a treatment approach for patients with positive intraoperative cultures during fracture nonunion surgery. The authors performed a retrospective case series at a level I trauma center. In this series, 60 patients without preoperative concern for infection were surgically treated for fracture nonunion. The treatment course of patients after fracture nonunion surgery, including culture results, antibiotic administration, and the presence of clinical infection and radiographic union, was studied. Sixty patients underwent fracture nonunion surgery. Twenty-four patients had a positive intraoperative culture. Fourteen patients had only a positive broth culture, 6 had only a positive routine culture, and 4 had positive mixed (routine and broth) cultures. The most common bacteria was coagulase-negative staphylococci, isolated in 19 of 24 patients, and the only isolated organism in 13 of 24 patients. Patients with a positive broth culture were not treated with antibiotics. Four of 10 patients with either a positive routine or mixed culture grown within 3 days of surgery were treated with antibiotics. All patients achieved clinical healing without signs of infection, and all but 2 patients achieved radiographic union at a mean follow-up of approximately 5 years. In the setting of fracture nonunion surgery, patients with only a positive broth culture and those with only a positive routine or mixed cultures that grew in a delayed fashion (>3 days postoperatively) did not require antibiotic treatment to achieve healing. [Orthopedics. 2019; 42(6):e532-e538.].

Non-union: Indications for external fixation

External fixation is currently used as the definitive mode of fracture stabilisation in the management of ˜50% of long-bone non-unions. Distinction between non-union and delayed union is a diagnostic dilemma especially in fractures healing by primary bone repair. This distinction is important, as non-unions are not necessarily part of the same spectrum as delayed unions. The aetiology of a fracture non-union is usually multifactorial and the factors can be broadly categorized into mechanical factors, biological (local and systemic) factors, and infection. Infection is present in ˜40% of fracture non-unions, often after open fractures or impaired wound healing, but in 5% of all non-unions infection is present without any clinical or serological suspicion. General indications for external fixation include clinical scenarios where; 1) percutaneous correction of alignment, or mechanical stimulation of the non-union site is required; 2) fixation of juxta-articular or 'emmental' bone fragments is necessary; and 3) staged bone or soft tissue reconstruction is anticipated. Specific anatomical indications include infected non-unions of the tibia, humerus, and juxta-articular bone. External fixation is an essential tool in the management of fracture non-unions. However, with greater understanding of the outcomes associated with both external and internal fixation the relative indications are now being refined.

Validation of a novel molecular diagnostic panel for pediatric musculoskeletal infections: Integration of the Cepheid Xpert MRSA/SA SSTI and laboratory-developed real-time PCR assays for clindamycin resistance genes and Kingella kingae detection

BACKGROUND

Pathogen detection in pediatric patients with musculoskeletal infections relies on conventional bacterial culture, which is slow and can delay antimicrobial optimization. The ability to rapidly identify causative agents and antimicrobial resistance genes in these infections may improve clinical care.

METHODS

Convenience specimens from bone and joint samples submitted for culture to Children's Hospital Colorado (CHCO) from June 2012 to October 2016 were evaluated using a "Musculoskeletal Diagnostic Panel" (MDP) consisting of the Xpert MRSA/SA SSTI real-time PCR (qPCR, Cepheid) and laboratory-developed qPCRs for Kingella kingae detection and erm genes A, B, and C which confer clindamycin resistance. Results from the MDP were compared to culture and antimicrobial susceptibility testing (AST) results.

RESULTS

A total of 184 source specimens from 125 patients were tested. The sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) of the Xpert MRSA/SA SSTI compared to culture and AST results were 85%, 98%, 93%, and 95% respectively for MSSA and 82%, 100%, 100%, and 99% for MRSA. Compared to phenotypic clindamycin resistance in S. aureus isolates, the erm A, B, and C gene PCRs collectively demonstrated a sensitivity, specificity, PPV, and NPV of 80%, 96%, 67%, and 98%. In comparison to clinical truth, Kingella PCR had a sensitivity, specificity, PPV, and NPV of 100%, 99.5%, 100%, and 100%.

CONCLUSIONS

This novel MDP offers a rapid, sensitive, and specific option for pathogen detection in pediatric patients with musculoskeletal infections.

Management of Early Deep Wound Infection After Thoracolumbar Instrumentation: Continuous Irrigation Suction System versus Vacuum-Assisted Closure System

STUDY DESIGN

A retrospective study.

OBJECTIVE

The aim of this study was to compare the clinical outcomes of continuous irrigation suction systems (CISS) or vacuum-assisted closure system (VACS) in early deep wound infection (DWI) after thoracolumbar instrumentation.

SUMMARY OF BACKGROUND DATA

DWI after thoracolumbar instrumentation is challenging and debridement followed by either CISS or VACS has been proven to be effective. So far, which one of the system has more advantages over the other remains unclear.

METHODS

Patients after thoracolumbar instrumentation were evaluated at our spine surgery center from 2005 to 2015. Patients who were diagnosed with early deep DWI after spinal instrumentation and treated by meticulous debridement in the operating room followed by either CISS or VACS were included. Detailed information was obtained from the medical records, including clinical features, results of laboratory examinations, medical therapies, and outcomes. A follow-up was conducted to observe whether recurrent spinal infection or other complications happened.

RESULTS

We identified 11 patients in the CISS group and 12 patients in the VACS group. There were no significant differences in terms of age, gender, follow-up duration, symptoms of infection, laboratory examinations, etc. The number of CISS or VACS replacement was 1.3 and 1.6, respectively, before wound healing (P > 0.05). And there were significant differences in terms of hospital stay and extra cost of infection treatment between the two groups. In the follow-up period, we observed sinus tract formation and low back pain in both groups and one patient in the VACS group died of pulmonary infection 4 years after the initial surgery.

CONCLUSION

Thorough debridement followed by CISS or VACS are comparable in treating early DWI after thoracolumbar instrumentation. The CISS treatment was statistically significant in comparison to the VACS treatment in terms of hospital stay and cost.

LEVEL OF EVIDENCE

4.

Non-union after plate fixation

Approximately a third of patients presenting with long-bone non-union have undergone plate fixation as their primary procedure. In the assessment of a potential fracture non-union it is critical to understand the plating technique that the surgeon was intending to achieve at the primary procedure, i.e. whether it was direct or indirect fracture repair. The distinction between delayed union and non-union is a diagnostic dilemma especially in plated fractures, healing by primary bone repair. The distinction is important as nonunions are not necessarily part of the same spectrum as delayed unions. The etiology of a fracture non-union is usually multifactorial and the factors can be broadly categorized into mechanical factors, biological (local and systemic) factors, and infection. Infection is present in ~40% of fracture non-unions, often after open fractures or impaired wound healing, but in 5% of all non-unions infection is present without any clinical or serological suspicion. Methods to improve the sensitivity of investigation in the search of infection include the use of; sonication of implants, direct inoculation of theatre specimens into broth, and histological examination of non-union site tissue. Awareness should be given to the potential anti-osteogenic effect of bisphosphonates (in primary fracture repair) and certain classes of antibiotics. Early cases of delayed/non-union with sufficient mechanical stability and biologically active bone can be managed by stimulation of fracture healing. Late presenting non-union typically requires revision of the fixation construct and stimulation of the callus to induce fracture union.

Deep sternal wound infection after cardiac surgery: a comparison of three different wound infection types and an analysis of antibiotic resistance

Background

Deep sternal wound infection (DSWI) is a severe complication following cardiac surgery. We compared epidemiology, clinical features, and microbiology of three types of DSWI and examined the antibiotic resistance in DSWI patients.

Methods

From 2011 to 2015, 170 adult post-cardiac surgery DSWI patients were recruited for this study and underwent the pectoralis major muscle flap transposition in our department.

Results

Of 170 adult patients with DSWI (mean age of 54 years), the majority (99 patients, 58.2%) had type II DSWI. The three types of DSWI patients showed significant differences in terms of gender, smoking history, chronic obstructive pulmonary disease (COPD), length of intensive care unit (ICU) stay, and hospitalization cost (P<0.05). The most common symptoms of DSWI patients were fever and wound dehiscence accompanied by purulent secretions. Types I and II DSWI were more frequently associated with hypoproteinemia and high leucocyte count (P<0.05). Microbiological diagnosis was available for 77 of 170 patients (45.3%). Of 157 pathogens detected, 87 (55.4%) species of gram negative bacilli were identified and most commonly were Pseudomonas aeruginosa (25.5%) and methicillin-susceptible Staphylococcus aureus (20.4%). However, no statistically significant microbiological differences among the three DSWI types were observed (P>0.05). Notably, P. aeruginosa isolates showed 100% resistance to cefazolin and cefuroxime. Meanwhile, the resistance rate of Acinetobacter baumannii isolates to commonly used antibiotics was greater than 70%, while resistance rates of staphylococcus to penicillin-G were 100% and to clindamycin were over 70%. No isolates were resistant to vancomycin, linezolid, and tigecycline.

Conclusions

Three types of DSWI exhibit differences in epidemiology and clinical features. P. aeruginosa and S. aureus are the most common pathogens in DSWI patients and antibiotic resistance is a serious concern in these patients. Therefore, prevention and treatment of DSWI should be closely tailored to clinical features, local microbiological characteristics, and resistance patterns of commonly encountered pathogens.

Prosthetic Device Infections

The immunocompromised host is a particularly vulnerable population in whom routine and unusual infections can easily and frequently occur. Prosthetic devices are commonly used in these patients and the infections associated with those devices present a number of challenges for both the microbiologist and the clinician. Biofilms play a major role in device-related infections, which may contribute to failed attempts to recover organisms from routine culture methods. Moreover, device-related microorganisms can be difficult to eradicate by antibiotic therapy alone. Changes in clinical practice and advances in laboratory diagnostics have provided significant improvements in the detection and accurate diagnosis of device-related infections. Disruption of the bacterial biofilm plays an essential role in recovering the causative agent in culture. Various culture and nucleic acid amplification techniques are more accurate to guide directed treatment regimens. This chapter reviews the performance characteristics of currently available diagnostic assays and summarizes published guidelines, where available, for addressing suspected infected prosthetic devices.

Microbiological Diagnosis of Implant-Related Infections: Scientific Evidence and Cost/Benefit Analysis of Routine Antibiofilm Processing

Prosthetic joint infection is one of the most severe complication following joint arthroplasty, producing a significant worsening of patient's quality of life. Management of PJIs requires extended courses of antimicrobial therapy, multiple surgical interventions and prolonged hospital stay, with a consequent economic burden, which is thought to markedly increase in the next years due to the expected burden in total joint arthroplasties. The present review summarizes the present knowledge on microbiological diagnosis of prosthetic joint infections, focusing on aethiological agents and discussing pros and cons of the available strategies for their diagnosis.Intra-operative clinical diagnosis and pathogen identification is considered the diagnostic benchmark, however the presence of bacterial biofilm makes pathogen detection with traditional microbiological techniques highly ineffective. Diagnosis of PJIs is a rather complex challenge for orthopedics and requires a strict collaboration between different specialists: orthopaedics, infectivologists, microbiologists, pathologists and radiologists. Diagnostic criteria have been described by national and international association and scientific societies. Clinicians should be trained on how to use it, but more importantly they should know potential and limitation of the available tests in order to use them appropriately.