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Arjun's PM copy-Microbiology and Infection > MI: Wound, bone and joint infections > Flashcards

MI: Wound, bone and joint infections Flashcards

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1
Q

Name three major pathogens that cause surgical site infections.

A
  • Staphylococcus aureus
  • Escherichia coli
  • Pseudomonas aeruginosa
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2
Q

List some factors affecting the severity of the disease.

A
  • Pathogenicity of the microorganism
  • Inoculum of the microorganism
  • Host immune response
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3
Q

What threshold of contamination of a surgical site is associated with increased risk of surgical site infections?

A

More than 10^5 organisms per gram of tissue

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4
Q

How does the dose of contaminating material required to establish infection change with prosthetic material?

A

Reduced

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5
Q

What are the three levels of surgical site infections?

A
  • 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
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6
Q

How is a surgical site infection caused by MRSA treated?

A

IV linezolid (oxazolidinone class)

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7
Q

List some risk factors for surgical site infections.

A
  • Age
  • ASA score of 3 or more
  • Diabetes (±postop hyperglycaemia)
  • Malnutrition
  • Hypoalbuminaemia
  • Radiotherapy and steroids
  • Rheumatoid arthritis (stop DMARDs 4 weeks before and until 8 weeks after operation)
  • Obesity (adipose tissue is poorly vascularised)
  • Smoking (delayed wound healing)
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8
Q

What should patients be advised to do on the day of the operation?

A

Shower with soap

on day / day before surgery

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9
Q

Why should shaving be avoided as a method of hair removal in surgery?

A

It can cause microabrasians which promote bacterial multiplication (electric clipper should be used instead)

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10
Q

Who should be offered nasal decontamination?

A

Patients who are found to be carrying S. aureus

(esp. cardiothoracic surgery)

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11
Q

When should antibiotic prophylaxis be given for patients undergoing surgery?

A

At the induction of anaesthesia

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12
Q

List some intra-operative measures that reduce the risk of surgical site infection.

A
  • Limit the number of people in the operating theatre
  • Ventilation of the theatre (positive pressure)
    ortho = laminar flow
  • Sterilisation of surgical instruments
  • Skin preparation (using povidone-iodine or chlorhexidine in 70% alcohol)
  • Asepsis and surgical technique
  • Normothermia (hypothermia causes vasoconstriction and decreases oxygen delivery to the wound space thereby increasing the risk of infection)
  • Oxygenation >95%
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13
Q

List some risk factors for septic arthritis.

A
  • Rheumatoid arthritis
  • Osteoarthritis
  • Crystal arthritis
  • Joint prosthesis
  • IVDU
  • Diabetes, chronic renal diesase, chronic liver disease
  • Immunosuppression
  • Trauma (e.g. intra-articular injection, penetrating injury)
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14
Q

Outline the pathophysiology of septic arthritis.

A
  • Proliferation of bacteria in the synovial fluid leads to generation of a host inflammatory response
  • Joint damage leads to exposure of host-derived protein (e.g. fibronectin) to which bacteria can adhere
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15
Q

List some bacterial factors that enable bacteria to cause septic arthritis.

A
  • Staphylococcus aureus has receptors such as fibronectin-binding protein
  • Kingella kingae have bacterial pili which adhere to the synovium (septic arthritis in children)
  • Some strains of S. aureus produce Panton-Valentine Leukocidin which is associated with fulminant infections
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16
Q

List some host factors that damage the joint in septic arthritis

A
  • Leukocyte-derived proteases and cytokines - joint damage
  • Raised intra-articular pressure - impairs blood flow leading to ischaemia
  • Genetic variation in cytokine expression - may lead to reduced immune response
17
Q

List some organisms that can cause septic arthritis.

A
  • Staphylococcus aureus (46%)
  • Streptococci (22%) (pyogenes, pneumoniae, agalactiae)
  • Gram-negative organisms (E. coli, H. influenzae, N. gonorrhoeae and Salmonella)
  • Coagulase-negative staphylococci (4%)
  • RARE: Lyme disease, Brucellosis, Mycobacteria, Fungi
18
Q

Describe the clinical features of septic arthritis.

A

1-2 week history of red, painful, swollen joint with restricted movement

NOTE: 90% monoarticular, 50% knee involvement

NOTE: patients with rheumatoid arthritis may have more subtle signs

19
Q

List some investigations for septic arthritis.

A
  • Blood culture before antibiotics
  • Synovial fluid aspiration (send for MC&S)
  • ESR and CRP
20
Q

What WBC in synovial fluid aspirate is suggestive of septic arthritis?

A

> 50,000 cells/ml

21
Q

Which imaging techniques are used in septic arthritis

A

Ultrasound - shows effusion and guides needle aspiration

MRI - shows joint effusion, cartilage destruction, abscess, contigous osteomyelitis

22
Q

How should septic arthritis be managed?

A
  • Antibiotics
  • Drainage of the joint (arthroscopic washout) - if infection does not respond to ABx
23
Q

Describe the antibiotic regime in septic arthritis

A

Flucloxacillin

  • 2 weeks IV (OPAT)
  • 4 weeks oral

Vancomycin if MRSA

Gonococcal or gram-negative infection - cefotaxime/ceftriaxone

24
Q

What are the two possible ways in which vertebral osteomyelitis can occur?

A
  • Acute haematogenous spread (bacteraemia)
  • Exogenous (implant during disc surgery)
25
Q

List some organisms that can cause vertebral osteomyelitis.

A
  • Staphylococcus aureus (48%)
  • Streptococcus (43.1%)
  • Gram-negative rods (23.1%)
  • Coagulase-negative staphylococcus
26
Q

In which region of the vertebral column is vertebral osteomyelitis most common?

A

Lumbar (43%)

Cervical (10.6%)

27
Q

What are the symptoms of vertebral osteomyelitis?

A
  • Back pain
  • Fever
  • Neurological impairment
28
Q

List some investigations for vertebral osteomyelitis.

A
  • MRI (90% sensitive)
  • Blood cultures
  • CT-guided/open biopsy
29
Q

How is vertebral osteomyelitis treated?

A

Antibiotics (at least 6 weeks)

Surgery if there is spinal cord compression

30
Q

Outline the presentation of chronic osteomyelitis.

A
  • Pain
  • Brodie’s abscess - intraosseous abcess
  • Sinus tract
31
Q

How is chronic osteomyelitis diagnosed?

A
  • MRI
  • Bone biopsy for culture and histology
32
Q

How is chronic osteomyelitis treated?

A
  • Radical debridement down to living bone
  • Sequestrectomy - remove sequestra (dead bone tissue) and infected bone disease
33
Q

What are the clinical features of prosthetic joint infection?

A
  • Pain
  • Early failure
  • Sinus tract
34
Q

Which organism most commonly causes prosthetic joint infection?

A
  • Coagulase-negative staphylococcus
  • Staph aureus
  • Gram-negative less likely
    Others: streptococci, enterococci, enterobacteriaciae, Pseudomonas aeruginosa, anaerobes
35
Q

How is prosthetic joint infection diagnosed?

A
  • Radiology - shows loosening of the prosthesis
  • Joint aspiration WCC (>1700/mL if knee; >4200/mL if hip)
36
Q

How should specimens be taken intraoperatively?

A
  • 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
37
Q

What is the difference between single stage revision and two stage revision?

A

Single stage revision

  • 1 surgical procedure
  • Remove all foreign material and dead bone
  • Re-implant new prosthesis with antibody-impregnated cement and give IV antibiotics

Two stage revision

  • 2 surgical procedures
  • Remove prosthesis and put in a spacer
  • Take samples for microbiology and histology
  • Period of IV antibiotics for 6 weeks then stop for 2 weeks
  • Re-debride and sample at second stage
  • Re-implantation with antibody impregnated cement
  • If antibiotics are needed, OPAT is used

Arjun's PM copy-Microbiology and Infection (26 decks)

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