Microbiology Flashcards
Which bones does osteomyelitis usually occur in
One of the long bones
What are some of the classifications of osteomyelitis
Acute or chronic - refers to speed of onset
Contiguous or haematogenous - either spread locally or through blood
How can osteomyelitis infection present
As micro abscess in the metaphis
Or as a infected pus filled abscess
How do you diagnose osteomyelitis
Clinical suspicion from history and examination
Can take swab to help pick treatment - not always diagnostic
GOLD STANDARD - bone biopsy
Why is swabbing a site of osteomyelitis not always useful
warm wet place so will have bugs growing that may not be causing issue
Not always diagnostic
What is the best imaging technique for osteomyelitis
MRI scan
How do you treat osteomyelitis
Surgical debridement to remove infected tissue
Antimicrobials to back up - wait for microbiology results
Do you ever start empirical antimicrobial treatment for osteomyelitis
ONLY if there are signs of sepsis
Otherwise wait for microbiology results
How long does it take to treat osteomyelitis
In general 6 weeks
This is because debrided bone takes 6 weeks to be covered by vascularised soft tissue
What is the antibiotic of choice for staph aureus
flucloxacillin
What is an obvious clinical sign of osteomyelitis
If you can see tendon or probe a bone
How can open fractures lead to osteomyelitis
Contiguous infection
Bone is open to air etc
Common pathogens are staph aureus and aerobic gram negatic bacteria
What is the key sign that a fracture has become infected
non-union of bone and poor wound healing
What are some features of diabetic foot
Micro neurovascular dysfunction Ischaemia Diminished sensation Deformity in toes and arch Ulceration
What feature of a diabetic foot commonly leads on to osteomyelitis
Ulcers
Probe to bone is the best sign as diagnosis can be hard
What is the best way to determine the bacterial cause of osteomyelitis
A bone biopsy
What types of bacteria does gentamicin treat
Gram negative
How long is antibiotic treatment for skin and soft tissue infection
7 days
How long is antibiotic treatment for blood
infection
14 days
Which antimicrobials might you use to treat osteomyelitis
Gram + cover: flucloxacillin (vancomycin if pen allergic)
Oral switch to doxycycline
Gram -ve cover: gentamicin IV if severe
Why do you switch to oral doxycycline rather than oral flucloxacillin in osteomyelitis
Bone penetration of doxy is great
Fluclox has poor bone penetration
Which groups are most likely to get haematogenous osteomyelitis
Prepubertal children
PWID
Central lines, dialysis patients, elderly
What would you do if a central line led to haematogenous osteomyelitis
Remove the line immediately
Keep doing blood cultures and treat until you get a negative result
What are the key pathogens for haematogenous osteomyelitis in PWIDs
Staph and Strep
Particularly aureus and viridans respectively
More likely to have unusual pathogens
What sites are common for PWIDs to develop infection
In unusual sites with unusual pathogens
Sternoclavicular
Sternochondral joints, Sacroiliac joint
Pubic symphysis
What is the most common pathogen to cause haematogenous osteomyelitis in dialysis patients
Staph aureus - due to colonisation
Aerobic gram negatives
What is clavicle ostemyeltis
A rarer site of the infection
Often caused by neck surgery or subclavian vein catheritsation
What is osteitis pubis
Another unusual site of bone inflammation
Occurs in the pubic bones
Can be triggered by surgery and its seen in athletes
Describe sickle cell osteomyelitis
Common infectious complication in those with sickle cell anaemia - 12%
Get acute long bone osteomyelitis
What are the most common pathogens in sickle cell osteomyelitis
Salmonella
Staphylococcus aureus
What is Gaucher’s disease
Lysosomal storage disorder - affects tibia
May mimic bone crisis
Usually sterile but can be infected by staph aureus
What are SAPHO and CRMO
Synovitis Acne Pustolosis Hyperostosis Osteitis
Chronic Recurrent Multifocal Osteomyelitis
Both unusual and rare conditions
What are the symptoms of SAPHO and CRMO
Fever, weight loss, generalised malaise
Multifocal osteitis
How does vertebral osteomyelitis usually occur
Mostly spreads through the blood - haematogenous
What are some potential causes of vertebral osteomyelitis
Epidural or Psoas abscesses PWID IV sites STIs or GU infections Post-op
What are some symptoms of vertebral osteomyelitis
Fever
Pain and tenderness
Raised inflammatory markers
Neurological symptoms
How do you diagnose vertebral osteomyelitis
Biopsy
May need to do several or progress to open biopsy
How do you treat vertebral osteomyelitis
Drain any abscesses
Put onto antimicrobials for 6 weeks
Do you need to have pulmonary TB to get it in the spine (or other bones)
No
Less than half presenting with vertebral TB have the lung condition
What are the risk factors for infection in prosthetic joints
Rheumatoid arthritis
Diabetes
Obesity
Malnutrition
How can a prosthetic joint become infected
Direct inoculation of pathogen at time of surgery
Due to joint manipulation in surgery
Seeding of joint at later time e.g. via blood
What is a common sign of prothesis becoming infected
Signs at the wound site and the wound opening up again
What conditions can be caused by PVL producing staph aureus
Skin infections
Necrotising pneumonia
Invasive infection
How do you treat PVL producing staph aureus infections
Flucloxacillin, clindamycin, linezolid, depending on sensitivities
What is the best way to treat a prothesis infection
Remove the prosthesis
Give antimicrobial therapy for at least 6 weeks
Replace if possible
How do you diagnose prosthesis infections
Culture samples taken during operation
Blood culture
CRP
Radiology
Which STI can cause septic arthritis
Gonorrhoea
Neisseria gonorrheae
How do you treat septic arthritis
Start empirical treatment with flucloxacillin (high dose)
Alter if needed when you confirm the organism
What is pyomositis
Bacterial infection of the skeletal muscles which results in a pus-filled abscess
90% staph cuased
Common in temperate areas and the immunosuppressed
How do you treat pyomyositis
Multidisciplinary approach - plastics, orthopaedics, infection
Needs wide local excision
Antibiotics often don’t help
How do you treat tetanus
Surgical debridement. Antitoxin Supportive measures such as intubation, beta blocker etc Antibiotics- penicillin / metronidazole Booster vaccination
What are the 5 key signs of infection
Rubor - redness Calor - heat Dolor - pain Tumour - swelling Loss of function
When should you start antibiotic treatment
ONLY once you know which bug you are treating - wait for culture and lab confirmation
EXCEPTION is if sepsis or meningitis is suspected, therefore empirical treatment may be life saving
What are some useful blood tests in infection
C -reactive protein - inflammatory marker that can be sensitive to infection
Plasma viscosity
Occasionally blood cultures, WCC and ESR
This
Mostly post-traumatic - e.g. open fractures
Then occurs in children
Immunosuppression
How must you treat a bone infection when there is pus present
Must physically remove the pus and any dead material from the area
Antibiotics will not get rid of pus
What is an involucrum
This is formed when infection gets under the periosteum and raises it up
New bone forms from this periosteum and starts a new layer
Occurs in chronic osteomyelitis
How does septic arthritis occur
Infection gets into joint via inoculation Spreads from the metaphysis of bone
Spreads through the blood
Describe necrotising fasciitis
Soft tissue infection Life-threatening Often occurs in the immunocompromised Bacteria may produce gas that gets into the tissue Needs emergency surgery
What tests would you do if you suspected infection in a replacement joint
CRP
Joint aspiration
Bone scan
X ray
What prophylaxis can be given against infection during/after surgery
Clean air theatres
Hand hygiene
Local antibiotics - in bone cement
Systemic antibiotics - IV
Which bugs do you normally use prophylaxis for after surgery
Staph aureus
Staph epidermidis
