MSK infections Flashcards
what are streptococcus coagulase -ve beta haemolytic
- Group A strep (throat, skin infections)
- Group B strep (neonatal meningitis)
- Group C, G etc
what are streptococcus catalase -ve, gamma-haemolytic (non haemolytic)
- enterococcus (gut commensals, UTI)
- e.faecalis
- e.faecium
what are streptococcus catalase -ve alpha haemolytic
- strep pneumoniae (pneumonia)
- strep viridins ( commensals, endocarditis)
what are staphylococcus coagulase +ve
staph.aureus (wound, skin infections)
what are staphylococcus coagulates negative
staph.epidermidis
what is the only coagulase positive staph
s.aureus
what enzyme does staph aureus produce
produces enzymes including coagulase, an enzyme that clots plasma. This distinguishes it from other staph species
what antibiotics are active in staph aureus
Flucloxacillin Cefazoline Vancomycin Teicoplanin Daptomycin
what is osteomyelitis
Osteomyelitis is an infection that usually causes pain in the long bones in the legs.
what is the pathogenesis of osteomyelitis
- Blood flow slowed and turbulent predisposing to bacterial seeding
- Area is a catch basin for bacteria and abscess may form
- Abscess spreads transversely along Volkmann canals and elevates periosteum
- Segment of devitalised bone remains within it.
- Occasionally abscess is walled off by fibrosis and bone sclerosis to form Brodie abscess
- Infectious process may erode periosteum and form sinus through soft tissues and skin to drain externally
what is the route of bacteria of osteomyelitis
HEMATOGENOUS - through blood. Monobacterial
- Children = long bones
- Adults = vertebrae
CONTIGUOUS - polimicrobial
- Young = injuries and surgery
- Elderly = pressure sore, vascular insufficiency
- DM = soft tissue infections, neuropathy, vascular insufficiency
what is the bacteria that causes osteomyelitis in children, adults and elderly
children = s.aureus, Group B strep adults = staphylococcus aureus elderly = frequency of gram negative bacteria increased
what are the principles of diagnoses for osteomyelitis
SUSPECT
- Patient medical history and epidemiology
- Examination (probe to bone/visible bone, non healing ulcer, sinus)
SAMPLE (gold standard is a biopsy)
- wound swabs/blood cultures not always diagnostic
- histology
TREAT (await microbial diagnoses)
- unless sepsis
when is the only time you should do antimicrobials before culturing
sepsis or soft tissue infection
what ways can osteomyelitis come about
- open fractures
- diabetes/ vascular insufficiency/ neuropathy
- haemoatogeneous osteomyelitis
- vertebral osteomyelitis
- specific hosts and pathogens
how can osteomyelitis come about from open fractures
- Contiguous infection/ direct spread
- Polymicrobial
- Early management is key (aggressive debridement, fixation and soft tissue cover)
- Clinical cue: non-union and poor wound healing
- Staphylococcus aureus and aerobic gram negative bacteria
how can osteomyelitis come about in diabetes/venous insufficiency
- contiguous infection
- polymicrobial
- investigations: probe to bone, plain radiograph, MRI
- treatment: debridement and antimicrobials
what would be the treatment taken for a antibiotic nave (no previous antibiotics for DFU in previous month) patient with diabetic foot ulcer osteomyelitis
6 weeks therapy initially
For acute presentation usually 2 weeks of IV therapy initially
ACUTE
- flucloxacillin 2g qds (IV)
- consider additional gram negative and anaerobic cover as per severe regime if patient not improving
CHRONIC
- avoid empirical treatment and use pathogen directed therapy from biopsy results
what would be the treatment for a non antibiotic naive patient with osteomyelitis diabetic foot ulcer
ACUTE:
- Vancomycin (IV) aim for prepose level 15-20mg/l
- consider additional gram negative anaerobic cover as per severe regime if patient not improving
CHRONIC
- avoid empirical treatment and use pathogen directed therapy from biopsy results
- if empirical treatment requires to be initiated recommend doxycycline 100mg bd (oral) +/- metronidazole 400mg tds (oral)
what antimicrobial is used for gram positive cover
- flucloxacillin (IV) for staph
- vancomycin instead of flucloxacillin for penicillin allergy
- oral switch for gram positive is doxycycline (bone penetration excellent)
what antimicrobial is used for gram negative over
- Gentamicin/Aztreonam IV if severe
- Oral cotrimoxazole/doxycycline if suitable for oral treatments
who is at risk for getting haematogeneous osteomyelitis
Prepubertal children People who inject drugs Central lines/dialysis Elderly Special conditions (ie sickle cell)
what is Gauchers disease
rare genetic disorder passed down from parents to children (inherited). When you have Gaucher disease, you are missing an enzyme that breaks down fatty substances called lipid
what are features of vertebral osteomyelitis
- mostly haematogenous
- may be associated with: epidural abscess, psoas abscess
what are clinical features of vertebral osteomyelitis
- fever
- insidious pain and tenderness
- neurological signs/symptoms
- raised inflammatory markers
- raised white cell count
how do you treat vertebral osteomyelitis
- drainage of large paravertebral/epidural abscess
- antimicrobials for 6 weeks minimum
- Expect 50% decrease in ESR/CRP
- duration extended in complicated cases
- MRI repeated only if unexplained increase in inflammatory markers, increasing pain, new anatomically related signs/symptoms
