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Week 7 - microbiology > Bone and joint infection WIP > Flashcards

Bone and joint infection WIP Flashcards

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1
Q

Describe the typical presentation of septic arthritis

A
  • New onset joint pain in the absence of trauma
  • hot, red, swollen joint (effusion)
  • Reduced range of motion
  • Sepsis
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2
Q

What are the differentials associated with septic arthritis?

A
  • Rheumatoid arthritis
  • Psoriatic arthritis
  • Crystal induced arthritis
  • Trauma
  • Haemarthrosis
  • extra-articular infection (cellulitis/bursitis)
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3
Q

What are the three types of causes of septic arthritis?

A
  • Haematogenous (arising from a distant site e.g. infective endocarditis)
  • Direct inoculation (e.g. following arthroscopy or trauma)
  • Contiguous spread e.g. cellulitis
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4
Q

What investigations should be carried out in a suspected septic arthritis?

A
  • Blood cultures (sepsis 6)
  • FBC, CRP, ESR, U&Es, LFTs
  • Joint aspirate looking at the synovial white cell count, microscopy and gram stain and under polarised light to look for evidence of crystals
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5
Q

Describe blood culture one it gets given to the lab

A
  • Loaded into an automated culture system
  • Aggregated and intubated
  • Colorimetric sensor in the bottom of each bottle with a pH sensitive dye which changes colour in the presence of CO2 indicating that the bottle is motive
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6
Q

Describe the process of gram staining

A
  • Crystal violet applied, staining all purple
  • Iodine acts as a fixative
  • Alcohol wash removes the purple stain from gram -ve
  • Application of safranin stains the gram negative organisms pink
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7
Q

What is a high white cell count in the synovial fluid suggestive of?

A
  • May indicate septic arthritis

* May also occur with crystal induced arthritis or inflammatory arthritis

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8
Q

What is a low synovial white cell count suggestive of?

A
  • Early infections
  • Immunocompromised
  • Prior antibiotic use
  • Low virulence organisms
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9
Q

What are the caustative micro-organisms of septic arthritis?

A
  • Staphylococcus aureus
  • Streptococci
  • Enterobacteriaceae (coliforms)
  • Mycobaterium tuberculosis
  • Neisseria gonorrhoeae
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10
Q

What are the causative microorganisms in septic arthritis in children?

A
  • Streptococcus pneumoniae
  • Kingella kingae
  • Haemophilius influenza type b
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11
Q

If the blood culture of someone with septic arthritis comes back positive for staphylococcus aureus, what additional tests should be carried out?

A
  • Skin swab for culture
  • look for infective endocarditis
  • Blood cultures, echocardiogram if positive
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12
Q

If the blood cultures of someone with septic arthritis come back positive for viridian’s streptococci, what additional investigations should be carried out?

A
  • Mouth, infective endocarditis

* Blood culture, trnasthroacic echocardiogram if positive

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13
Q

If the blood cultures of someone with septic arthritis come back positive for enterobacteriaceae/enterococci, what investigations should be carried out?

A
  • Source: abdomen or urogenital tract

* Urine culture, imaging of the abdomen pelvis

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14
Q

What antibiotics should be prescribed for a patient with staphylococcus aureus positive septic arthritis?

A
  • IV flucloxacillin if methicillin susceptible

* IV vancomycin if methicillin resistant or beta lactam allergy

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15
Q

What antibiotics should be prescribe for someone with a streptococcus spp. positive septic arthritis?

A
  • IV benzylpenicillin or ceftriaxone

* IV vancomycin if allergy

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16
Q

What antibiotic should be prescribed in a enterococcus spp. positive septic arthritis?

A
  • IV amoxicillin

* IV vancomycin

17
Q

What antibiotic should be prescribed in a neisseria gonorrhoea positive septic arthritis?

A

IV ceftriaxone

18
Q

What are the impacts of a periprosthetic joint infection?

A
  • Pain
  • Reduced mobility
  • Draining sinus
  • Revision surgery
  • Prolonged hospital stay
  • Long antibiotic course
  • Financial cost
19
Q

Explain the role of biofilm in prosthetic joint infection

A
  • Microorganisms adhere to surface and secrete extracellular substances to form complex glycocalyx structure
  • Microorganisms located within biofilm slowly start diving and evade the host defences (quorum sensing) and become more resistant to antimicrobial therapy
  • Eradication of the infection may not be possible without removal of the prosthesis/biofilm
20
Q

Describe Acute prosthetic joint infection

A
  • Red, hot, painful joint
  • Fever/sepsis
  • Prolonged leaking gowned post-operatively
21
Q

Describe chronic prosthetic joint infection

A
  • Pain
  • Stiffness
  • Loosening of prosthesis on X ray
  • May be mildly raised inflammatory markers
  • Difficult to distinguish from aseptic loosening
22
Q

What investigations should be carried out in someone presenting with acute prosthetic joint infection?

A
  • Joint aspirate - WCC, microscopy and culture

* Blood cultures

23
Q

What investigations should be carried out in someone presenting with chronic prosthetic joint infection?

A
  • Look for sinus tract

* Joint aspirate

24
Q

Describe the diagnosis of PJI

A
  • Stop antibiotics at least two weeks prior to surgery
  • Send multiple (5-6) samples: pus, fluid, synovium, membrane, bone
  • Separate sites with separate sterile instruments
  • Do not send swabs/sinus samples (poorer sensitivity)
25
Q

Describe beadmill processing

A
  • Shaking with glass beads to disrupt biofilm

* Bacteria dissociates from the biofilm

26
Q

Describe sanitation fo explanted prosthesis

A

Low intensity ultrasound to disintegrate biofilm

27
Q

What are the surgical strategies to treat prosthetic joint infection?

A
  • Debridement, antibiotics and implant retention - radical debridement, thorough joint washout and exchange of polythene liners (only if immature)
  • Complete removal of the prosthesis in a one or two stage exchange
  • Resection without reimplantation
  • amputation
28
Q

Describe the antimicrobial management of prosthetic joint infection

A

•Delay until theatre samples are taken unless septic or clinically unstable
•Empirical gram negative and positive cover
•If the metalwork is retained, biofilm active antibiotics should be used (staph= rifampicin, gram neg
rod = ciprofloxacin)
•Empirical therapy = IV vancomycin and IV gentamicin
•6 weeks following removal, 3-6 months DAIR or single stage revision

Week 7 - microbiology (12 decks)

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