1 / 47

MICROBIOLOGY OF PROSTHETIC JOINT INFECTIONS

MICROBIOLOGY OF PROSTHETIC JOINT INFECTIONS. Dr Robert Nelson. SIR JOHN CHARNLEY FRCS FRS. Pioneer of low friction arthroplasty. Established a Unit at Wrightington in 1961. PROSTHETIC JOINT INFECTION. Early realisation of the risks of infection. Airborne contamination suspected

linda-welch
Download Presentation

MICROBIOLOGY OF PROSTHETIC JOINT INFECTIONS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. MICROBIOLOGY OF PROSTHETIC JOINT INFECTIONS Dr Robert Nelson

  2. SIR JOHN CHARNLEY FRCS FRS • Pioneer of low friction arthroplasty. • Established a Unit at Wrightington in 1961.

  3. PROSTHETIC JOINT INFECTION • Early realisation of the risks of infection. • Airborne contamination suspected • Pioneer in ultra-clean ventilation for operating theatres.

  4. JOINT REPLACEMENTS IN ENGLAND AND WALES: • 1995 = 75,000. • 2012 = 184,113.

  5. WHAT IS BEING REPLACED? • 98% are hips and knees. • Remainder are mostly shoulders. • Ankle replacement remains unusual.

  6. INFECTION RATES Over the lifetime of the joint: • Hip = 1%. • Knee = 2%.

  7. CLASSIFICATION OF PJI • Early onset: less than 3 months • Delayed onset: 3 months to 1 - 2 years • Late onset: >1 - 2 years.

  8. EARLY ONSET • Organisms gain entry at the time of operation. • Generally a virulent infection. • Wound drainage, erythema, oedema, pain. • Staphylococcus aureus / MRSA. • Coliforms. • Mixed infections.

  9. DELAYED ONSET • Also gain entry around the time of operation. • Take much longer to manifest. • Symptoms are less severe. • Pain in the joint. • Sinus formation may occur. • Coagulase-negative Staphylococcus spp. • Propionibacterium spp.

  10. LATE ONSET • Spread from a distant source of infection. • 50% have no apparent source • Likely to be acute. • Staphylococcus aureus. • E. coli. • Coliforms.

  11. FEATURES OF PJI • Bulk of infections are caused by Staphylococcal species (approximately 50%). • Propionibacterium may be more common in shoulder joint infections. • Staphylococcus aureus has a higher incidence in patients with rheumatoid arthritis. • Small colony variants may be an issue.

  12. SMALL COLONY VARIANTS • Formed by S.aureus. • Non-pigmented and non-haemolytic colonies one-tenth of normal size on culture. • Auxotrophs for haemin or menadione. • May persist intracellularly.

  13. BIOFILM AND PJI • Presence of a foreign body significantly reduces inoculum required to establish infection. • Bacteria elaborate an exopolysaccharide which encases them and adheres to the prosthesis. This is a biofilm. • Organisms embedded in the biofilm are metabolically inert and more resistant to antibiotics.

  14. BIOFILM AND PJI • Delayed onset of symptoms following surgery. • Difficulty in demonstrating organisms in aspirates of delayed onset infection. • Antibiotic treatment may initially result in response and then relapse. • Long term suppression may be successful.

  15. MICROBIOLOGICAL DIAGNOSIS

  16. THE DILEMMA Skin flora is the predominant cause of PJI. • Is the culture clinically significant? • Did it come instead from the patient’s skin? • Did it arise from Theatre staff? • Did the Laboratory contaminate it?

  17. DEFINITION OF PJI • Presence of a sinus track that communicates with joint. • Presence of acute inflammation on histopathology. • Presence of pus surrounding the prosthesis.

  18. CULTURE IS STILL REQUIRED • Scans are unhelpful. • Molecular methods have not been helpful to date. • ID and sensitivity results from cultures greatly assist in patient management.

  19. PREOPERATIVE PRECAUTIONS • Stop all concurrent antibiotic therapy for at least two weeks prior to aspirate or surgery. • Obtain all prior culture results from your own and other hospitals. • Consider a preoperative joint aspirate.

  20. PREOPERATIVE ASPIRATE • Should be done under strict aseptic conditions. • Usually arrives in blood culture bottles. • Gram and cell count may be helpful. • Essential that any isolate has full identification and sensitivity testing.

  21. DEALING WITH THE RESULT • Patients rapidly discharged home. • Is the result significant? • What do we do when we grow virulent organisms?

  22. OPERATIVE CULTURES • How many should we take? • How should we handle them?

  23. NUMBER OF SAMPLES • “Osiris” Paper 1995. • Send at least 5-6 samples. • Single positive sample is unlikely to be significant. • Isolation of indistinguishable microorganisms from three or more independent specimens is highly predictive of infection. • Sensitivity 65% specificity 99.6%. • Gram staining sensitivity 12% specificity 98%

  24. TAKING SAMPLES • Separate scalpel / container for each specimen. • Take prior to prophylactic antibiotics • Aim for abnormal areas, particularly membranes between bone cement interfaces. • Transport promptly to the Laboratory.

  25. LABORATORY PROCESSING • Vortexing with Ballotini sterile glass beads is simple with a low risk of contamination. • Beads are superior to shaking in broth alone. • Use homogenate to inoculate cultures.

  26. CULTURES • Broth culture is essential given the low numbers of organisms present in samples. • RCM, FAA or equivalent are suitable. • Direct culture on plates is optional. • SCV’s require chocolate agar to grow.

  27. BROTH CULTURES • Inspect daily for visible turbidity. • Sub culture if turbid. • Terminal sub culture at five days.

  28. SHOULD WE BE INCUBATING FOR LONGER? • Evidence suggests a 7 day culture only isolates 73% of pathogens. • Extending incubation to 14 days increases yield. • Predominantly Propionibacterium spp,Peptostreptococcus and diphtheroids. • Increases isolation of contaminants.

  29. WHAT ABOUT THE PROSTHESIS? • Prosthesis will have many organisms adherent in biofilm. • Large and heavy piece of metal. • Difficult to transport and process aseptically. • Leakage a significant problem. • Enlarged specimen containers may be the answer.

  30. BACTERIAL ISOLATES • Regard every isolate as potentially significant. • Identify every isolate. • Full sensitivity panel. • MIC for relevant glycopeptides. • Preserve isolates until all culture work is complete.

  31. SENSITIVITY TESTING • Guides initial choice of agents. • IV and oral options are required. • Alternatives for intolerant patients. • Valuable information for determining significance. • Monitoring of resistance trends. • Information for future cement choices.

  32. TREATMENT • Stop antibiotics if infection is excluded. • Narrow coverage based on sensitivities. • Provide treatment plan for IV followed by oral course. • Antibiotic cement in future procedures.

More Related