Approach to Surgical Infections (Wound vs Prosthetic)

Question 1

def of a wound infection

Answer 1

Within 30 days after surgery, only include skin, subcut tissues, deep layers or distant organs and have purulent drainage or organisms isolated from the wound site

Question 2

what is considered a prosthetic?

Answer 2

Prosthesis: foreign body

Question 3

the viral load amount to infect a prosthetic joint vs a native joint is _____________

Answer 3

lower

Question 4

RF for a prosthetic joint infection

Answer 4

Preop RF: hx of prior surgery at arthroplasty site, current bacteremia/sepsis, prev/active infection at current surg site, hx of multiple arthroplasties, a prev joint infection, intra-articular injections within the 3M before surgery

Modifiable RF: smoking, alcohol, IV drug use, poor oral hygiene, malnutrition, poor preop glycemic control, obesity, poorly controlled comorbidities (DM, liver, kidney, HIV, use of immunosuppressants)

Nonmodifiable RF: genetics → first- or second-degree relative with a hx of joint infection

Operative RF: ↑ surgical time and complexity

Question 5

common bacteria for early, delayed, and late prosthetic infections

Answer 5

early (within 4wks) - Staphylococcus aureus – high virulence so can infect early

delayed (3-12M postop) - staphylococcus epidermidis

late (2-3Y) - staph aureus

Question 6

typical pathogenesis entry point for pathogen for early, delayed, and late prosthetic infections

Answer 6

early - localized dissemination

delayed - localized or hematogenous

late - hematogenous spread

Question 7

what makes prosthetic infections so difficult to treat?

Answer 7

biofilms

Question 8

why are biofilms more difficult to target?

Answer 8

acts as a barrier vs antimicrobial agents and host immune response, so a higher concentration of abx is required to achieve bactericidal activity

Question 9

how are biofilms created?

Answer 9

1. free floating bacteria have surface contact and adhere to the surface
2. there is irreversible attachment and they begin to form/produce biofilm matrix in a single layer
3. they mature and form multilayer microcolonies
4. a matured biofilm has characteristic “mushroom” shape which can burst and allow for the bacteria to disperse and start the process again

*within the mushroom shape the bacteria can communicate and share resistance genes

Question 10

what is a biofilm?

Answer 10

a community of surface-attached or non-surface attached bacteria ➔ bacterial aggregates

Question 11

how does someone with a prosthetic joint infection present? s/s

Answer 11

pain w/ affected joint – may be very red, w/ persistent wound drainage and decrease ROM (5 signs of inflammation)

*may lack systemic s/s and fever

there is a specific criteria for dx - not needed to know

Question 12

how do you work up a sus prosthetic joint infection?

Answer 12

standard w/u: blood culture, CRSP, ESR, WBC count, Xray
➔ sus persists: bone/soft tissue biopsy/aspiration + advanced imaging tests (MRI bone scan or Indium/WBC nuclear med scan)

1. Find the source!
   - blood culture, synovial fluid culture, surgical wound swabbing for C&S and gram stain, tissue culture
2. Bloodwork: CBC w/diff, inflammatory markers (CRP, ESR), glucose
3. imaging - xray, indium scan (WBCs will travel potentially travel to source of inflammation), bone scan

Question 13

what preventative steps can we take to stop a prosthetic joint infection from occuring?

Answer 13

1. good surgical infection prevention (scrub, disinfectants, OR traffic)
2. prophylactic abx - cefazolin for gen pop; add vanco for increase risk of MRSA

Question 14

how do we tx prosthetic joint infections?

Answer 14

1. surgical debridement or removal of hardware – refer to ortho for options
2. antibiotic tx for >=6wks

*aim to target S. aureus, MRSA, and GN bacilli

in prosthetic joint infections, rifampin and fluoroquniolones are often used as empiric bc it penetrates biofilms well