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MICRO ADYA > Microbiology 12 - Wound, bone and joint infections > Flashcards

Microbiology 12 - Wound, bone and joint infections Flashcards

1
Q

Important pathogens implicated in wound infections

A
  1. Staph auerus (MSSA or MRSA)
  2. E Coli
  3. Pseudomonas
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2
Q

What infectious dose increases the risk of surgical site infections?

A

>10^5 g/L

*lower if there is foreign material in the wound

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3
Q

What is the major pathogen involved in wound, bone and joint infections?

A

MRSA/ MSSA

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4
Q

What are the 3 levels of wound infection?

A

Superficial incisional- skin and subcutaneous tissue
Deep incisional- fascial and muscle
Organ/ space infection- any part of anatomy other than incision

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5
Q

Recall 2 important risk factors for wound/ bone/ joint infection

A

Diabetes
Obesity (adipose tissue is poorly-vascularised)

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6
Q

What is the most important independent risk factor for SSI following cardiothoracic surgery?

A

Nasal contamination with Staph Aureus

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7
Q

Reducing risk of surgical site infections: pre-operative

A

pre-operative

  1. Treating other infections
  2. Underlying illnesses
    - ASA score of 3 or more indicates having systemic disease
    - Diabetes- risk of post operative hypoglycaemia
    - Malnutrition
    - Radiotherapy and steroids: need to taper steroids preoperatively
    - Rheumatoid arthritis: stop DMARDS 4 weeks before and 8 weeks postoperatively
    - Obesity: due to poor vascularisation + oxygenation of adipose tissue
  3. Smoking cessation: increased vascular resitance = delayed immune response
  4. Pre-operative Showering:
  5. Avoiding hair removal or using electric clippers:
  6. Nasal Decontamination for staph aureus
  7. Antibiotic Prophylaxis: bactericidal concentration of drug should be present at time of incision. with additional doses if significant blood loss or delayed procedure
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8
Q

What can be done during orthpaedic procedures to reduce risk of infection?

A

Laminar flow

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9
Q

Why do patients need to be kept at normothermia in theatre?

A

Mild hypothermia increases the risk of surgical site infections because of vasoconstriction - reduced oxygenation/wound healing

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10
Q

Reducing risk of surgical site infections: intra-operative

A

ventilation = positive pressure and 20 air changes/hour

skin preparation with povidone-iodine or chlorhexidine.

  • Trust recommendation: Chlorhexidine in 70% alcohol is used

prevent hypothermia: warm IV fluids and warm irrigation fluids and start forced airwarming if temperature <36

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11
Q

Which patient group is particularly at risk of septic arthritis?

A

Those who already have rheumatoid arthritis

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12
Q

What organism most commonly causes septic arthritis?

A

Staph aureus - most common in adults- and also most likely to cause joint destruction

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13
Q

Which organism causes septic arthritis in young sexually active people?

A

N. Gonorrhoea

Spreads haematogneously from an initial infection

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14
Q

Other causatvie organisms of septic arthritis

A
  1. Staph aureus (most common)
  2. Strep - strep pyogenes, strep pneumoniae, strep aglagatiae
  3. gram negatives - N gonorrhoea, E. Coli, Salmonella, Haemophilus influenzae
    * Coagulase negative staphylococci- 4% incidence
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15
Q

Example of coagulase negative staph

A

Staph epidermidis

(Staphylococcus saprophyticus - UTIs not wound)

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16
Q

Where in the joint do organisms adhere to in septic arthritis?

A

Synovial membrane

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17
Q

What are the symptoms of septic arthritis?

A

Red, painful and swollen joint with *restricted movement*

\

*mostly monoarticular, and most affect the knee

*rhematoid arthritis patients- septic arthritis signs may not be as clear cut

18
Q

What investigations for septic arthritis should be done before starting antibiotics?

A
  1. Blood cultures
  2. Synovial fluid aspiration and culture (>50,000 WBC/mm^3)

both the above should be done before starting antibiotics

  1. Bloods: CRP, ESP, WCC
  2. USS to confirm effusion and guide aspiration

*however a negative culture does not negate septic arthritis

19
Q

When is MRI indicated for septic arthritis patients?

A

When osteomyelitis is suspected

20
Q

How is septic arthritis managed?

A

4-6 weeks IV antibiotics

joint aspiration: either arthroscopically or clsoed needle aspiration

Surgical washout/drainage may be needed in more complicated/severe cases

21
Q

What are the symptoms of vertebral osteomyelitis?

A

Back pain and fever

often localised tenderness on percussion of the vertebrae

neurological symptoms

22
Q

Routes of infection for vertebral osteomyelitis + risk factors

A

Routes of infection: exogenous (eg disc surgery or spinal injection) or haematogenous from bacteraemia

23
Q

What is the most common pathogen implicated in vertebral osteomyelitis?

A

Staph Auerus

Followed by:

  • coagulase negative staph eg staph epidermidis
  • gram negative rods
  • streptococcus
  • rare: brucella (causes less well defined granulomas than TB)
24
Q

How is osteomyelitis diagnosed?

A

MRI

*to identify causative organism

  • blood culture if haematogenous route suspected
  • CT guided or open biopsy for culture
25
Q

How is vertebral osteomyelitis treated?

A

At least 6w of antibiotics

26
Q

Which part of the spine is most commonly affected in vertebral ostemyelitis?

A
  • LUMBAR SPINE (43.1%)
  • Cervical (10.6%)
27
Q

Features of brucella + treatment

A

Histology: vague granuloma (not as well defined as TB)

Culture: silvery colonies on agar

Treatment: rifampicin, ciprofloxacin, doxycycline

28
Q

How does prosthetic joint infection present?

A

Pain

Patient complain that the joint was ‘never right’ after the operation

Early failure

Sinus tract:

  • abnormal channel through the soft tissues that allows communication between a joint prosthesis and the outside environment
  • known or presumed to be colonised by bacteria
29
Q

What is the most common pathogen implicated in prosthetic joint infections?

A

Coagulase negative staphylococcus eg staph epidermidis

Followed by staph aureus, enterococcus

30
Q

What would an x ray show in prosthetic joint infections?

A

lysis and loosening

31
Q

How many tissue samples are required for the lab when a patient goes to theatre for a suspected joint infection?

A

5 (If >3 yield same organism = infection)

32
Q

What are the 2 options for management of prosthetic joint infection?

A
  1. Single stage revision (removal of manky prosthesis and replacement with antibiotic-impregnated material prosthesis)
  2. Two stage revision (firstly remove prosthesis and send off samples, put in a spacer, give antibiotics, wait a few weeks, stop antibiotics, rebride and sample, then put new antibiotic impregnanted prosthesis in)
33
Q
A
34
Q

How does chronic osteomyelitis present?

A

Prolonged pain and fever

  • Pain
  • Brodie’s abscess
  • Sinus tract
35
Q

Chronic osteomyelitis: pathophysiology

A

Primary infection not cleared

Formation of:

a) sequestrum- necrotic bone that separates off from normal bone- and
b) involucrum - new bone formed by osteoblasts that surrounds the sequestrum

36
Q

IVX and MX of chronic osteomyelitis

A

IVX: bone biopsy + culture is diagnostic

  • MRI usually
  • Biopsy and culture for histology to find causative organism

MX: surgical debridement to remove sequestra of affected bone + antibiotics

37
Q

Which pathogen is commonly implicated in wounds in diabetic patients?

A

Pseudmonas- usually infects opportunistically

38
Q

risk factors for septic arthritis

A
  • Rheumatoid arthritis, osteoarthritis, crystal induced arthritis
  • Joint prostheses
  • IV drug abuse
  • Diabetes
  • Chronic renal disease, chronic liver disease
  • Immunosuppression- steroids
  • Trauma- intra-articular injection, penetrating injury
39
Q

Pathophysiology of septic arthritis

A
  • Organisms adhere to the synovial membrane
  • Bacterial proliferation occurs in the synovial fluid with generation of a host inflammatory response
  • Joint damage Þ exposure of host-derived proteins such as fibronectin, which bacteria adhere to
40
Q

bacterial factors causing septic arthritis

A
  • S. aureus has receptors such as fibronectin binding protein that recognise selected host proteins
  • Kingella kingae have bacterial pili which adhere to the synovium
41
Q

host factors causing septic arthritis

A
  • Leucocyte derived proteases and cytokines can lead to cartilage degradation** and **bone loss

​

  • Raised intra-articular pressure can hamper capillary blood flow** and lead to **cartilage and bone ischemia and necrosis

genetic variation in cytokines = different susceptibility to response

42
Q

TWO methods used to treat Chronic Osteomyelitis

A

Modified Lautenbach Technique]

  • debrididing and removing necrotic bone. introduce antibiotics to area
  • every week 1L of Hartmann’s solution is infused through each drain. Suction fluid is sent for culture + tailor antibiotics to culture
  • PO antibiotics continued for 6 weeks after discharge

Papineau Technique- MORE RECENT​

  • Complete excision of infected tissue and necrotic bone + bone grafting

MICRO ADYA (22 decks)

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