Micro: Wound, Bone and Joint Infections Flashcards
Aetiology of surgical site infection
Wound contamination - dependent on bacterial flora on site of infection. Severity of disease witll depend on pathogenicity of microorganism and host immune response.
What threshold of contamination of a surgical site is associated with increased risk of surgical site infections?
More than 10^5 organisms per gram of tissue
Lower dose of microorganisms required if foreign material present (e.g. sutures, prosthesis)
Name three major pathogens that cause surgical site infections.
- Staphylococcus aureus
- Escherichia coli
- Pseudomonas aeruginosa
What are the three levels of surgical site infections?
- Superficial incisional - skin and subcutaneous tissues
- Deep incisional - fascial and muscle layers
- Organ/space infection - any part of the anatomy that is not the incision
Patient Risk factors for surgical site infections
- Older age
- Diabetes
- Smoking
- Obesity
- Steroids
impact wound healing
Signs and Symptoms of Surgical site infections
Pain, swelling in incision area
Failure of wound healing
Management of surgical site infection
Abx: Fluclox for Staph / Linezolid if MRSA
Prevention measures for surgical site infections
Pre-op (showering of pts, nasal decontamination if Staph A carrier, prophylactic abx given at induction of anaesthesia - bacterialcidal levels achieved by incision)
Intra-op (limiting ppl in theatre, ventilation, normothermia)
Aetiology for septic arthritis
Local or haematological (bacteriaemia) spread to joint
Organism adheres to synovial membrane resulting in host inflammatory response. Increased intraarticular pressure results in further bone damage which exposes host-derived proteins (e.g. fibronectin) which further bacteria (e.g. Staph A) can bind to
Risk factors for septic arthritis
- RA
- IVDU
- Joint prosthesis
- DM
- Immunosuppression
- Trauma
List common organisms that can cause septic arthritis
- Staph. Aureus (commonest)
- Strep
- E.coli
- N. gonorrhoea (if young)
List some bacterial factors that enable bacteria to cause septic arthritis.
- Staphylococcus aureus has receptors such as fibronectin-binding protein
- Kingella kingae have bacterial pili which adhere to the synovium
Clinical features of Septic Arthrits
- ACUTE history of red, swollen, painful joint (monoarticular)
- Fever
- Restricted movement
Commonest joint = knee!
Investigations for septic arthrits
- Blood culture (if febrile)
- Joint aspirate + MC&S (WCC synovial count >50k = septic arthritis likely)
- MRI (for joint effusion, articular cartilage destruction, bone abscess, osteomyelitis)
Management of septic arthritis
IV Abx - Cephalosporin or Fluclox (good response at 2w = switch to oral)
+
Arthroscopic washout
Aetiology of osteomyelitis
- Acute haematogenous spread (bacteriaemia)
- Direct (e.g. septic arthritis)
- Exogenous (from surgery - implant or prosthesis)
Vertebral is most common (lumbar > thoracic-cervical > cervical)
Commonest organisms causing vertebral osteomyelitis
- Staphylococcus aureus
- Streptococcus
- Coagulase-negative staphylococcus
- Gram-negative rods
What are the symptoms of vertebral osteomyelitis?
- Back pain
- Swelling
- Fever
- Neurological impairment
Investigations for osteomyelitis
- MRI
- Blood cultures (if septic)
- CT-guided/open biopsy (if blood culture comes back -ve)
Treatment for osteomyelitis
Abx for at least 6 weeks
debridement second line or if chronic osteomyelitis
Common organisms causing prosthetic joint infection
- Coagulase-negative staphylococcus
- Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
Clinical Features of prosthetic joint infection
- Red, hot, swollen joint
- Joint failure - “joint never right since operation”
- Sinus tract
Diagnosis of prosthetic joint infection
- Radiology (XR/CT/MRI) - shows loosening of the prosthesis
- CRP > 13.5 for prosthetic knees
- CRP > 5 for prosthetic hips
- Joint aspiration WCC (>1700/mL if knee; >4200/mL if hip)
BE CAUTIOUS OF JOINT ASPIRATION AS IF NOT INFECTED BEFORE IT CAN BECOME INFECTED AFTER ASPIRATION ATTEMPT
How should specimens be taken intraoperatively?
- Specimens should be taken from at least 5 sites around the implant and sent for histology
- NOTE: if 3 or more specimens yield identical organisms, this is suggestive of prosthetic joint infection
