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YR5 Microbiology > Wound, Bone and Joint Infections > Flashcards

Wound, Bone and Joint Infections Flashcards

1
Q

What are the 3 major pathogens in surgical site infection?

A

Staph.aureus (MSSA + MRSA)

E.coli

Pseudomonas aeruginosa

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2
Q

What is the pathogenesis of a surgical site infection?

A
  • Contamination of wound at operation
  • Pathogenicity + innoculum of microorganisms
  • Host immune response

If surgical site is contaminated with > 10^5 microorganisms per gram of tissue, risk of SSI is increased.

Dose of contaminating bacteria required to cause infection is much lower if foreign material is present e.g silk suture.

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3
Q

What are the three levels of surgical site infection?

A

Superficial incisional: Affect skin + subcutaneous tissue.

Deep incisional: Affect fascial + muscle layers.

Organ/ space infection: Any part of anatomy other than incision.

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4
Q

A patient is admitted, with a SAH + subdural haemorrhage after a fall.

Decompressive craniectomy.

In April, they had a cranioplasty with titanium plate.

Pt was readmitted in Oct with large subdural collection with midline shift + had a subsequent abscess evacuation.

Titanium plates removed.

Underneath there was severe infection with 1-1.5cm thick pus.

What is the likely organism? What drug should be commenced?

A

MRSA

IV Linezolid

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5
Q

What are three different phases where surgical site infections can be prevented?

A

Pre-operative phase

Intra-operative phase

Post-operative phase

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6
Q

What is the relationship between age and developing a surgical site infection?

A

Independent RF.

Direct linear trend of increasing risk until 65y

Age >75 was found to be a significant RF.

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7
Q

List 6 underlying illnesses are risk factors for a surgical site infection

A

ASA score of >,3

Diabetes: 2-3 fold increased risk. A/W post-op hyperglycaemia. Control blood glucose. HbA1C < 7.

Malnutrition

Low serum albumin

Radiotherapy + steroid use: Taper steroids.

Rheumatoid arthiritis: Stop disease modifying agents for 4w pre + 8w post-op.

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8
Q

Why is obesity a risk factor for surgical site infections?

A

Adipose tissue is poorly vascularised.

Poor oxygenation of tissues + functioning of immune response increases risk of SSIs.

Risk increased by 2-7 in patients with a BMI of >,35

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9
Q

How is smoking a risk factor for surgical site infections?

A

Smoking duration + no. of cigarettes smoked.

Nicotine delays primary wound healing.

Causes Peripheral vascular disease.

Vasocontrictive effect of nicotine reduces oxygen-carrying capacity of blood.

Encourage tobacco cessation pre-op

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10
Q

How can pre-operative showering affect the risk of surgical site infections?

A

Microorganisms colonising the skin may contaminate exposed tissues + cause an SSI.

No difference in SSI incidence when chlorhexidine or detergent/ bar soap is used.

Pts should be advised to shower or bath using soap on day of surgery/ day before.

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11
Q

How can hair removal affect the risk of surgical site infections?

A

Micro-abrasions caused by shaving with a razor may lead to multiplication of bacteria.

Use electric clippers on the day of surgery with single-use head.

Hair should not be removed unless it will interfere with the operation.

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12
Q

How can nasal decontamination affect the risk of surgical site infections?

A

S.aureus is carried in the nares of 20-30%.

An analysis demonstrated that S.aureus carriage was the most powerful independent RF for SSI following cardiothoracic surgery.

Nasal de-colonisation should be performed

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13
Q

How can antibiotic prophylaxis affect the risk of surgical site infections?

A

Abx prophylaxis should be given at induction of anaesthesia.

Bactericidal conc. of the drug should be established in serum + tissues at time of incision.

Additional doses may be necessary if significant blood loss or if operation prolonged.

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14
Q

How can ventilation affect the risk of surgical site infections?

A

Maintain positive pressure ventilation.

Maintain ~20 air changes per hour (>,3 must be fresh air).

Filter all air.

Keep operating room doors closed.

Consider laminar flow for orthopaedic implant surgery.

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15
Q

How can sterilisation affect the risk of surgical site infections?

A

Sterilise all surgical instruments.

Inadequate sterilisation of surgical instruments has resulted in SSI outbreaks.

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16
Q

How should skin be prepared to reduce the risk of surgical site infections?

A

When skin is incised microorganisms may contaminate tissues + cause an SSI.

Prepare skin at surgical site using antiseptic preparation using Chlorhexidine in 70% alcohol

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17
Q

What is an aseptic surgical technique?

A

Maintaining effective haemostasis while preserving adequate blood supply, gently handling tissues, avoiding inadvertent entries into hollow viscus, removing devitilised tissues + eradicating dead space.

Adhere to asepsis when placing intravascular devices or epidural catheters.

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18
Q

How does hypothermia affect the risk of surgical site infections?

A

Mild hypothermia: increase risk of SSIs by causing vasoconstriction, decreased delivery of O2 to wound space + subsequent impairment of neutrophil function.

In theatre suite: Measure pt temp before inducing anaesthesia. Start forced air warming if temp is <36ºC.

Warm IV fluid.

Warm irrigation fluid.

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19
Q

How does adequate oxygenation affect the risk of surgical site infections?

A

Maintain optimal oxygenation during surgery, to maintain a haemoglobin saturation > 95%.

Higher inspired O2 conc. in peri-operative period reduces SSIs.

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20
Q

What are three common bone and joint infections?

A

Septic arthritis

Chronic osteomyelitis

Prosthetic joint infection

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21
Q

What is the epidemiology and prognosis of septic arthritis?

A

Incidence: 2-10/ 100,000.

In pts with RA incidence: 28-38/ 100,000

Mortality: 7-15%.

Morbidity: 50%.

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22
Q

What are 6 risk factors for septic arthritis?

A

Rheumatoid arthritis, osteoarthritis, crystal induced arthritis

Joint prosthesis

IVDU

Diabetes, chronic renal/ liver disease

Immunosuppression: Steroids

Trauma: Intra-articular injection, penetrating injury

23
Q

What is the pathophysiology of septic arthritis?

A

Organisms adhere to synovial membrane, bacteria proliferate in synovial fluid with generation of host inflammatory response.

Joint damage leads to exposure of host derived proteins such as fibronectin to which bacteria adhere.

24
Q

What are bacterial factors for pathogenesis of septic arthritis?

A

S.aureus has receptors (fibronectin binding protein) that recognise selected host proteins.

Kingella kingae synovial adherence is via bacterial pili.

Some S. aureus strains produce cytotoxin PVL (Panton-Valentine Leucocidin) which have been associated with fulminant infections.

25
Q

What are host factors for the pathogenesis of septic arthritis?

A

Leucocyte derived proteases + cytokines can lead to cartilage degradation + bone loss.

Raised intra-articular pressure can hamper capillary blood flow + lead to cartilage + bone ischaemia + necrosis.

Genetic variation in expression of cytokines may lead to differential susceptibility

26
Q

What are the main causative organisms for septic arthritis?

A

Staph. aureus: 46%

Coagulase negative staphylococci 4%

Streptococci: 22%

(pyogenes, pneumoniae, agalactiae)

27
Q

List 4 gram negative causative organisms of septic arthritis

A

E.coli

Haemophilus influezae

Neisseria gonorrhoeae

Salmonella

28
Q

List 4 rare causative organisms of septic arthritis

A

Lyme

Brucellosis

Mycobacteria

Fungi

29
Q

What are clinical features of septic arthritis?

A

1-2w hx of red, painful, swollen restricted joint

  • Monoarticular in 90%
  • Knee involved in 50%
30
Q

How do patients with rheumatoid arthritis differ in clinical features of septic arthritis?

A

May show more subtle signs of joint infection.

31
Q

What are appropriate investigations for septic arthritis?

A
  • Blood culture before abx are given
  • Synovial fluid aspiration for microscopy + culture
  • ESR, CRP
32
Q

What synovial fluid results indicate septic arthritis?

A
  • Traditionally a synovial count >50,000 cells/mm3 suggested septic arthritis.
  • -ve culture result does NOT exclude septic arthritis.
33
Q

Which imaging modalities are useful for septic arthritis?

A

US: Confirm effusion + guide needle aspiration.

MRI: Joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis.

34
Q

What is the management for septic arthritis?

A

Abx: IV Cephalosporin or Flucloxacillin.

+/- Vancomycin if high risk of MRSA.

IV abx 2w, review

up to another 4w IV/ orally

Drainage: Arthoscopic washout

35
Q

What are two different classifications of vertebral osteomyelitis?

A

Acute haematogenous: bacteraemia seed to vertebrae

Exogenous: After disc surgery or Implant associated

36
Q

What are common causative organisms of vertebral osteomyelitis?

A

S.aureus: 48.3%

Strep: 43.1%

(C-veS: 6.7%)

(G-veR: 23.1%)

37
Q

What is the general localisation of vetebral osteomyelitis?

A

Cervical: 10.6%

Cervico-thoraco: 0.4%

Lumbar: 43.1%

38
Q

What are symptoms of vetebral osteomyelitis?

A

Back pain: 86%

Fever: 60%

Neurological impairment: 34%

39
Q

What are appropriate investigations for vertebral osteomyelitis?

A

MRI: 90% sensitive

Blood cultures

CT/open biopsy

40
Q

What is the management of vertebral osteomyelitis?

A

6w abx

Longer tx if undrained abscesses/ implant associated

Surgery if spinal cord compression

41
Q

What are signs and symptoms of a prosthetic joint infection?

A

Pain

Pt complains that the joint was ‘never right’

Early failure

Sinus tract

42
Q

What are the gram positive cocci causative of a prosthetic joint infection?

A

Coagulase negative staphylococci (most common)

Staphylococus aureus

Streptococci sp

Enterococci sp

43
Q

List 5 less common causative organisms of prosthetic joint infection

A

Aerobic gram -ve bacilli: Enterobacteriaceae + Pseudomonas aeruginosa

Anaerobes

Polymicrobial

Culture negative

Fungi

44
Q

What are investigations for a prosthetic joint infection?

A

Radiology: Loosening, sinus tract, communication with joint

CRP: >10

Joint aspiration: >3000 WBCs/ ml, >80% neutrophils

+ve immunoassay for alpha defensin

Histology: >5 neutrophils per high power field

45
Q

How is intraoperative microbiological sampling conducted?

A

Tissue specimens from>, 5 sites around the implant.

Histopathology: Infection defined as >5 neutrophils per high power field.

If >,3 specimens yield identical organisms, this is highly predictive of infection (sensitivity 65%, specificity 99%).

46
Q

What is single stage revision for a prosthetic joint infection?

A

Aspirate joint to identify pathogen.

Excision of infected tissue, synovectomy.

Add abx to bone cement according to culture results.

Implantation of a cemented hip or knee prosthesis using abx loaded cement.

Give 7-10d of IV abx.

Culture drain tips.

47
Q

What is two stage revision for a prosthetic joint infection?

A

Remove prosthesis.

Take samples for microbiology + histology.

Period of IV abx (6w). Stop abx for 2w.

Re-debride + sample at 2nd stage.

Re-implantation with abx impregnated cement.

No further abx if samples clear.

48
Q

How can theatre traffic be managed to reduce surgical site infections?

A

Microbial load in theatre related to no. people present

Theatre personnel should be minimised

49
Q

Which of the following is associated with a reduced risk of SSI:

Bactericidal concentration of antibiotic in serum at time of incision

Obesity

Smoking

Diabetes

A

Bactericidal concentration of antibiotic in serum at time of incision

50
Q

What does chronic osteomyelitis present with?

A

Pain

Brodies abscess (interposes abscess)

Sinus tract discharging pus

51
Q

What investigations are needed for chronic osteomyelitis?

A

MRI

Bone biopsy for culture + histology

52
Q

Name a technique used for chronic osteomyelitis

A

Masquelet technique (radical sequestrectomy)

Removal of foreign bodies, fill defect with abx loaded cement spacer + external fixation

In 6-8w remove spacer, fill defect with autologous bone graft

53
Q

What is recommended if PJI is detected within first 3 weeks of joint replacement?

A

Debridement, antibiotics, and implant retention (DAIR)

Tissue sampling

Radical debridement

Exchange of modular components

Abx for 6w+

YR5 Microbiology (23 decks)

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