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MSK > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Which bones does osteomyelitis usually occur in

A

One of the long bones

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2
Q

What are some of the classifications of osteomyelitis

A

Acute or chronic - refers to speed of onset

Contiguous or haematogenous - either spread locally or through blood

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3
Q

How can osteomyelitis infection present

A

As micro abscess in the metaphis

Or as a infected pus filled abscess

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4
Q

How do you diagnose osteomyelitis

A

Clinical suspicion from history and examination
Can take swab to help pick treatment - not always diagnostic
GOLD STANDARD - bone biopsy

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5
Q

Why is swabbing a site of osteomyelitis not always useful

A

warm wet place so will have bugs growing that may not be causing issue
Not always diagnostic

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6
Q

What is the best imaging technique for osteomyelitis

A

MRI scan

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7
Q

How do you treat osteomyelitis

A

Surgical debridement to remove infected tissue

Antimicrobials to back up - wait for microbiology results

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8
Q

Do you ever start empirical antimicrobial treatment for osteomyelitis

A

ONLY if there are signs of sepsis

Otherwise wait for microbiology results

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9
Q

How long does it take to treat osteomyelitis

A

In general 6 weeks

This is because debrided bone takes 6 weeks to be covered by vascularised soft tissue

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10
Q

What is the antibiotic of choice for staph aureus

A

flucloxacillin

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11
Q

What is an obvious clinical sign of osteomyelitis

A

If you can see tendon or probe a bone

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12
Q

How can open fractures lead to osteomyelitis

A

Contiguous infection
Bone is open to air etc
Common pathogens are staph aureus and aerobic gram negatic bacteria

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13
Q

What is the key sign that a fracture has become infected

A

non-union of bone and poor wound healing

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14
Q

What are some features of diabetic foot

A 
Micro neurovascular dysfunction 
Ischaemia 
Diminished sensation
Deformity in toes and 
arch 
Ulceration
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15
Q

What feature of a diabetic foot commonly leads on to osteomyelitis

A

Ulcers

Probe to bone is the best sign as diagnosis can be hard

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16
Q

What is the best way to determine the bacterial cause of osteomyelitis

A

A bone biopsy

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17
Q

What types of bacteria does gentamicin treat

A

Gram negative

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18
Q

How long is antibiotic treatment for skin and soft tissue infection

A

7 days

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19
Q

How long is antibiotic treatment for blood

infection

A

14 days

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20
Q

Which antimicrobials might you use to treat osteomyelitis

A

Gram + cover: flucloxacillin (vancomycin if pen allergic)
Oral switch to doxycycline
Gram -ve cover: gentamicin IV if severe

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21
Q

Why do you switch to oral doxycycline rather than oral flucloxacillin in osteomyelitis

A

Bone penetration of doxy is great

Fluclox has poor bone penetration

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22
Q

Which groups are most likely to get haematogenous osteomyelitis

A

Prepubertal children
PWID
Central lines, dialysis patients, elderly

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23
Q

What would you do if a central line led to haematogenous osteomyelitis

A

Remove the line immediately

Keep doing blood cultures and treat until you get a negative result

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24
Q

What are the key pathogens for haematogenous osteomyelitis in PWIDs

A

Staph and Strep
Particularly aureus and viridans respectively

More likely to have unusual pathogens

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25
Q

What sites are common for PWIDs to develop infection

A

In unusual sites with unusual pathogens
Sternoclavicular
Sternochondral joints, Sacroiliac joint
Pubic symphysis

26
Q

What is the most common pathogen to cause haematogenous osteomyelitis in dialysis patients

A

Staph aureus - due to colonisation

Aerobic gram negatives

27
Q

What is clavicle ostemyeltis

A

A rarer site of the infection

Often caused by neck surgery or subclavian vein catheritsation

28
Q

What is osteitis pubis

A

Another unusual site of bone inflammation
Occurs in the pubic bones
Can be triggered by surgery and its seen in athletes

29
Q

Describe sickle cell osteomyelitis

A

Common infectious complication in those with sickle cell anaemia - 12%
Get acute long bone osteomyelitis

30
Q

What are the most common pathogens in sickle cell osteomyelitis

A

Salmonella

Staphylococcus aureus

31
Q

What is Gaucher’s disease

A

Lysosomal storage disorder - affects tibia
May mimic bone crisis
Usually sterile but can be infected by staph aureus

32
Q

What are SAPHO and CRMO

A

Synovitis Acne Pustolosis Hyperostosis Osteitis

Chronic Recurrent Multifocal Osteomyelitis

Both unusual and rare conditions

33
Q

What are the symptoms of SAPHO and CRMO

A

Fever, weight loss, generalised malaise

Multifocal osteitis

34
Q

How does vertebral osteomyelitis usually occur

A

Mostly spreads through the blood - haematogenous

35
Q

What are some potential causes of vertebral osteomyelitis

A 
Epidural or Psoas abscesses 
PWID 
IV sites 
STIs or GU infections 
Post-op
36
Q

What are some symptoms of vertebral osteomyelitis

A

Fever
Pain and tenderness
Raised inflammatory markers
Neurological symptoms

37
Q

How do you diagnose vertebral osteomyelitis

A

Biopsy

May need to do several or progress to open biopsy

38
Q

How do you treat vertebral osteomyelitis

A

Drain any abscesses

Put onto antimicrobials for 6 weeks

39
Q

Do you need to have pulmonary TB to get it in the spine (or other bones)

A

No

Less than half presenting with vertebral TB have the lung condition

40
Q

What are the risk factors for infection in prosthetic joints

A

Rheumatoid arthritis
Diabetes
Obesity
Malnutrition

41
Q

How can a prosthetic joint become infected

A

Direct inoculation of pathogen at time of surgery
Due to joint manipulation in surgery
Seeding of joint at later time e.g. via blood

42
Q

What is a common sign of prothesis becoming infected

A

Signs at the wound site and the wound opening up again

43
Q

What conditions can be caused by PVL producing staph aureus

A

Skin infections
Necrotising pneumonia
Invasive infection

44
Q

How do you treat PVL producing staph aureus infections

A

Flucloxacillin, clindamycin, linezolid, depending on sensitivities

45
Q

What is the best way to treat a prothesis infection

A

Remove the prosthesis
Give antimicrobial therapy for at least 6 weeks
Replace if possible

46
Q

How do you diagnose prosthesis infections

A

Culture samples taken during operation
Blood culture
CRP
Radiology

47
Q

Which STI can cause septic arthritis

A

Gonorrhoea

Neisseria gonorrheae

48
Q

How do you treat septic arthritis

A

Start empirical treatment with flucloxacillin (high dose)

Alter if needed when you confirm the organism

49
Q

What is pyomositis

A

Bacterial infection of the skeletal muscles which results in a pus-filled abscess
90% staph cuased
Common in temperate areas and the immunosuppressed

50
Q

How do you treat pyomyositis

A

Multidisciplinary approach - plastics, orthopaedics, infection
Needs wide local excision
Antibiotics often don’t help

51
Q

How do you treat tetanus

A 
Surgical debridement.
Antitoxin 
Supportive measures such as intubation, beta blocker etc 
Antibiotics- penicillin / metronidazole
Booster vaccination
52
Q

What are the 5 key signs of infection

A 
Rubor - redness 
Calor - heat 
Dolor - pain 
Tumour - swelling 
Loss of function
53
Q

When should you start antibiotic treatment

A

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

54
Q

What are some useful blood tests in infection

A

C -reactive protein - inflammatory marker that can be sensitive to infection
Plasma viscosity

Occasionally blood cultures, WCC and ESR

55
Q

This

A

Mostly post-traumatic - e.g. open fractures
Then occurs in children
Immunosuppression

56
Q

How must you treat a bone infection when there is pus present

A

Must physically remove the pus and any dead material from the area
Antibiotics will not get rid of pus

57
Q

What is an involucrum

A

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

58
Q

How does septic arthritis occur

A

Infection gets into joint via inoculation Spreads from the metaphysis of bone
Spreads through the blood

59
Q

Describe necrotising fasciitis

A 
Soft tissue infection 
Life-threatening 
Often occurs in the immunocompromised 
Bacteria may produce gas that gets into the tissue 
Needs emergency surgery
60
Q

What tests would you do if you suspected infection in a replacement joint

A

CRP
Joint aspiration
Bone scan
X ray

61
Q

What prophylaxis can be given against infection during/after surgery

A

Clean air theatres
Hand hygiene
Local antibiotics - in bone cement
Systemic antibiotics - IV

62
Q

Which bugs do you normally use prophylaxis for after surgery

A

Staph aureus

Staph epidermidis

MSK (21 decks)

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