Microbiology of MSK infections Flashcards
What is the most common cause of osteomyelitis?
Staph aureus
What are the first line treatment choices for staph/strep infection?
Flucloxacillin
Vancomycin (pen allergic)
Clindamycin (virulent strain requiring anti-toxin)
What are the first line treatment choices for coliform infection?
Gentamicin Ceftriaxone (try to avoid) Ciprafloxacin (oral but try to avoid)
What makes infection of implanted devices so hard to treat?
Biofilm formation
What is a biofilm?
Bacterial growth coated in protein and polysaccharides
How do biofilms affect the environment of the area they’ve infected?
Reduce pH
Reduce oxygen availability
What are the three types of implant infection?
Early post-op
Delayed
Late
Which bacteria tend to cause early post-op implant infections?
Staph aureus
Streptococci
Enterococci
Which bacteria tend to cause delayed implant infections?
Coag. negative staph
P. acnes
Which bacteria tend to cause late implant infections?
Staph aureus
E.coli
Describe the time frame for each type of implant infection
Early post op - 0-3 mnth
Delayed - 3-24 mnth
Late - >24 mnth
How does an early implant infection present?
Fever
Effusion
Warmth
Drainage
How does a delayed implant infection present?
Persistant pain
Device loosening
Fistula
How does a late implant infection present?
Acute OR subacute
Describe the route of infection for each type of implant infection
Early - perioperative
Delayed - perioperative
Late - haematogenous
What is the diagnostic criteria for systemic inflammatory response syndrome (SIRS)?
Temperature >38 OR 90
Respiratory rate >20 OR PaCO2 12,000 OR
SIRS is an ongoing response in chronic infections. T/F
False - SIRS is only acute
What defines the need for immediate antibiotic treatment of a patient?
Presence of SIRS - immediate treatment
Absence of SIRS - delay until specimens cultured
How are prosthetic joint infections treated?
Debride joint
Long course of high dose (+/- IV) antibiotics
What are the two surgical options for prosthetic joint infection?
Debride and retain prosthetics (DAIR)
Debride and remove prosthetic (one or two stage)
What are the most common acute prosthetic joint infections?
Staph aureus
Strep
What are the most common chronic prosthetic joint infections?
Coag negative staph
Propionibacteria
What type of samples are obtained in PJI? Why?
Bone samples - reflect the infecting organism
How are gram positive joint infections treated?
Flucloxacillin/vancomycin
Teicoplanin (if resistant)
How are gram negative joint infections treated?
Co-trimoxazole
Amoxicillin
How long does DAIR treatment take?
4 weeks + 8 weeks
How long does one stage treatment take?
4 weeks + 6 weeks
How long does two stage treatment take?
6 weeks + 6 weeks
How long does hip treatment take?
3 months (12 weeks)
How long does knee treatment take?
6 months (24 weeks)
Is CPR always elevated?
No -
Usually normal in chronic infections
Can be influenced by underlying diseases
Can be influenced by surgery
How long should PJI treatment be continued after resolution of clinical symptoms and signs? What should then be done?
2 weeks
CT/MRI
When can we be sure of a clinical cure following PJI?
2 years post treatment
Describe surgical prophylaxis
Give dose 60min pre surgery
Stop dose within 24 hours post surgery
What surgical prophylaxis is given in orthopaedics?
Co-amoxiclav/co-tramoxazole peri op and two post op doses
Eradicate MRSA pre-op
What are the underlying risk factors for bone and joint infections (BJI)?
Immunosuppression Diabetes Implants IV drug user Sickle cell anaemia
Which BJI pathogen is common in children
Kingella
How does a BJI present acutely?
Fever
Inflammation over the affected joint
Reduced mobility/fixed immobilisation
How does a BJI present acutely in a child?
Listless
Not feeding
Not playing
Cranky
What is septic arthritis?
Infection of a joint space
What are the possible routes of infection with regard to septic arthritis?
Haematogenous
Contiguous (bone-bone)
Direct inoculation (injection, trauma, etc)
Which organisms tend to be involved in septic arthritis?
Staph aureus
Strep
H. influenzae (children)
Gonorrhoea
How is septic arthritis diagnosed?
Blood culture (IF FEVER) Inflammatory markers FBC U&E Lactate Joint aspirate +/- washout --> culture Crystals and gram stain USS X-ray/CT/MRI/bone scan
How is septic arthritis treated? How long for?
Flucloxacillin
Ceftriazone if
What is osteomyelitis?
Inflammation of bone/medullary cavity
Which bones tend to be affected by osteomyelitis?
Long bones
Vertebrae
Which pathogens tend to be involved in acute osteomyelitis?
S. aureus
Strep
Which pathogens tend to be involved in chronic osteomyelitis?
TB
Pseudomonas
Salmonella
Coliforms
When might osteomyelitis reoccur?
Inefficient treatment
Incidence os osteomyelitis is increasing in children. T/F
True
What are the possible routes of infection with regard to osteomyelitis?
Haematogenous
Contiguous (bone-bone)
Peripheral vascular disease associated
Prosthesis associated
Define the timeframe of acute osteomyeltis
What is the most likely route of infection in acute osteomyelitis?
Haematogenous
Acute osteomyelitis can become septic arthritis in which bones especially? Why?
Hip
Shoulder
Ankle
Elbow
Metaphyses are found within the joint space
Why are infants more at risk of osteomyelitis becoming septic arthritis?
They have blood vessels connecting the metaphysis to the epiphysis
Chronic osteomyeltis has a higher risk of which complications?
Abscess
Septicaemia
Permanent bone deformity
How should chronic osteomyelitis be managed?
Antibiotic treatment according to culture results (if no SIRS)
How is osteomyelitis diagnosed and managed? How long for?
Blood culture (IF FEVER)
Bone biopsy +/- washout –> culture
Empiric flucloxacillin
4-8 weeks
What are the risk factors for prosthetic joint infections?
Diabetes
Rheumatoid arthritis
Malnutrition
Obesity
Coagulate negative staph are skin commensals. T/F
True - this can make it difficult to determine whether they are contaminants or causing infections
Why can it be difficult to get a microbiology diagnosis of PJI? How can this be reduced?
Most infecting organisms are skin commensals
Multiple tissue and bone cultures
How can PJI be diagnosed?
Multiple tissue/bone cultures Blood culture (RARELY +VE) Inflammatory markers FBC Imaging
How is PJI treated?
Debridement
At least 6 weeks antibiotic treatment
Re-implant joint post - treatment
What is necrotising fasciitis?
Severe infection of subcutaneous soft tissues
How common is necrotising fasciitis?
Uncommon
How often to people die from necrotising fasciitis?
High mortality (rapidly progressive)
Where are the common sites of necrotising fasciitis infection?
Abdominal wall
Perineum
Limbs
Post-op wounds
How does necrotising fasciitis present?
Highly painful
Minimal signs of inflammation
Systemic symptoms
Rapid expansion
Describe type 1 and type 2 necrotising fasciitis
Type 1 - anaerobes (synergistic gangrene)
Type 2 - group A strep
How can necortising fasciitis be diagnosed?
Clinical Swabs + biopsy --> microbiology, gram stain, culture Blood culture Inflammatory markers FBC
How is necrotising fasciitis managed?
Debridement
Antibiotics
Which antibiotics are given in type 1 necrotising fasciitis?
Pip-taz
Clindamycin
Gentamicin
Which antibiotics are given in type 2 necrotising fasciitis?
Penicillin & clindamycin
Necrotising faciitis requires droplet protection. T/F
False - contact precautions
Which pathogen is responsible for gas gangrene?
Clostridium perfringens
Describe the pathogenesis of gas gangrene
Spores lie within tissues –>
Predisposition (dead tissue, hypoxia) –>
Multiplication –>
Accumulation of gas bubbles within tissue
On compression of an area with gas gangrene what can be felt?
Crepitus
How is gas gangrene managed?
Urgent debridement
High dose penicillin and/or metronizaole
+/- hyperbaric oxygen
What pathogen causes tetanus?
Clostridium tetani
Where can tetanus bacteria be found?
Animal mouths
Soil
Rust
How does tetanus present? Why?
Spastic paralysis
Lock jaw
Produces a neurotoxin which prevents release of neurotransmitters
How long is the incubation period of tetanus?
4 days - several weeks
How is tetanus treated?
Debridgement Anti-toxin Supportive Penicillin/metronidazole Toxoid booster vaccination
When are the tetanus vaccines given?
2, 3 & 4 months
