Microbiology 8: Wound, Bone And Joint Infections

Question 1

What are the 3 main organisms causing surgical site infections ?

Answer 1

Staphylococcus aureus
E.Coli
Pseudomonas aeruginosa

Question 2

Does shaving a patient using a razor increase or decrease the risk of surgical site infection ?

Answer 2

Increase- you are making micro-abrasions which can be an entry route for skin bacteria.

Question 3

List 3 bacterial factors that contribute to the risk of septic arthritis ?

Answer 3

• S.Aureus- fibronectin binding proteins (helps recognise selected host proteins)
• S.Aureus- Panton-Valentine leucocidin
• Kingella kingae- bacterial pili (help it adhere to synovium)

Question 4

Which bacterial factor is associated with more fulminant septic arthritis ?

Answer 4

Panton-valentine Leukocidin (S.aureus)

Question 5

Which organism is the most common cause of septic arthritis ?

Answer 5

S.aureus

Question 6

What is the most common organism responsible for vertebral osteomyelitis ?

Answer 6

S.aureus

Question 7

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

Answer 7

Lumbar spine

Question 8

What is the diagnostic investigation for vertebral Osteomyelitis ?

Answer 8

MRI scan

Question 9

Which techniques are used to treat Chronic osteomyelitis ?

Answer 9

• Lautenbach technique: debridement of infected/dead bone and insertion of 2 drains that allow delivery of antibiotics, fluids and irrigation.
• Papineau technique: complete excision of infected tissue and necrotic bone followed by cancellous bone grafting and skin grafting.

Question 10

What characteristic radiological finding of Prosthetic joint infection ?

Answer 10

Loosening (bone loss along the cement-bone interface)

Question 11

What is the treatment for prosthetic joint infection ? (2 stages)

Answer 11

Single stage revision- The old prosthesis and all infected/necrotic tissue and bone is debrided. A new prosthesis is put in place with antibiotics.

Two stage revision- The old prosthesis and all the infected/necrotic bone and tissue is debrided. A spacer is put in and the area is treated for 6 weeks with Antibiotics before a new prosthesis is put in place.

Question 12

Which organism is the most common cause of Prosthetic joint infection ?

Answer 12

Coagulase negative staphylococci - Staphylococcus epidermidis

Question 13

how many organisms must a surgical site be contaminated with to increase the risk of SSI

Answer 13

• >10^5 microorganisms
• dose of contaminating material is much lower where there is foreign material present

Question 14

name a gram positive coccus which is haemolytic and causes Surgical site infection

How do you treat this?

Answer 14

MRSA

treat with IV linezolid

Question 15

why is nasal decontamination done pre surgery

Answer 15

done if a patient is found to have S. Aureus in their nostrils

Question 16

what antiseptics are used to prepare the skin pre-surgery (2)

Answer 16

• povidine - iodine
• chlorhexidine 70% alcohol

Question 17

investigations for septic arthritis

Answer 17

• blood cultures BEFORE antibiotics
• synovial fluid aspiration - send for mc+s (synovial count >50,000 WBC/ml suggest septic arthritis)
• US
• CT - erosive bone change
• MRI - joint effusion, articular cartilage destruction

Question 18

management of septic arthritis

Answer 18

• antibiotics (4 weeks) - done via OPAT (outpatient parenteral antimicrobial therapy)
• drainage of the joint

Question 19

treatment for vertebral osteomyelitis

Answer 19

antibiotics - at least 6 weeks

Question 20

diagnosis of PJI

Answer 20

• radiology - loosening - bone loss along the cement-bone interface
• CRP>13.5 for prosthetic knee joint
• CRP>5 for hip
• joint aspiration (higher WCC = hip, whereas lower = knee)

Question 21

Vertebral osteomyelitis presentation

Answer 21

BACK PAIN + FEVER

Question 22

Old man had prosthetic joint inserted. What is likely organism causing infection?

Answer 22

Coagulase negative staphylococci