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MSK > Microbiology/Infection > Flashcards

Microbiology/Infection Flashcards

1
Q

What are the five cardinal clinical features of inflammation?

A 
Rubor - red
Calor - hot
Dolor - pain + tenderness 
Tumour - swelling
Functio laesa - loss of function
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2
Q

What are the two most useful blood tests in joint infection?

A

CRP

PV

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3
Q

What are the three ways you can get osteomyelitis?

What are the associated organisms?

A

(Acute) direct inoculation through open wound – Staph aureus
(Acute haematogenous) – children (haemophilus) or immunosuppressed
Secondary to contiguous local infection (with or without the presence of vascular disease

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4
Q

What must you do in a fragmented fracture?

A

Must surgically remove the fragments - they don’t have a blood supply so are highly susceptible to infection

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5
Q

What is the basic pathophysiology of osteomyelitis

A

Trauma causes clot formation in the vessels supplying the bone
This clot is susceptible to infection

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6
Q

What do bloods show in chronic osteomyelitis?

Management?

A

They are often unhelpful

Not everybody needs surgery - some people just live with it

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7
Q

What is an involucrum?

What condition is it a complication of?

A

A layer of new bone growth outside existing bone. It results from the stripping-off of the periosteum by the accumulation of pus within the bone, and new bone growing from the periosteum
Chronic osteomyelitis

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8
Q

What are the three aetiologies of septic arthritis?

Why is treatment urgent?

A

From inoculation
From metaphyseal spread
Direct haematogenous
Pus can destroy articular cartilage in a few days

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9
Q

What should you look for on x-ray of soft tissue infections?

A

Look for gas on the x-ray – caused by gas-forming organisms.

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10
Q

Which antibiotics should you use for cellulitis?

A

Best guess antibiotics to cover Staph and Strep

Ben Clift uses Flucloxacillin and benzylpenicillin

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11
Q

What can you feel on palpation of a patient with necrotizing fasciitis?

A

When you press the affected area it feels like bubble wrap – you can feel the popping

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12
Q

What is disciitis?

When should treatment be started?

A

Septic arthritis of a disc
Best guess antibiotics are acceptable here - do not wait for culture
Think Staph aureus

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13
Q

The infected arthroplasty
Is this superficial or deep infection?
Which two questions must you ask the patient?

A

This is deep infection, not a superficial wound problem.
Was there ever a wound problem?
Has it ever been pain free?

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14
Q

What is treatment for infected arthroplasty?

A

Take out the whole prosthesis and put in antibiotic cement

Leave it for ~3 months to clear, and then put in a new joint

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15
Q

What are the most common causative organisms for hip vs knee infected arthroplasty?

A 
Hips
- 16 CNS i.e. staph epidermis
- 13 staph-aureus
- 2 enterococcus
Knees
- 13 staph-aureus
- 9 CNS
- 4 pseudomonas
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16
Q

What is the general treatment for osteomyelitis?

A

Surgical debridement and antibiotics

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17
Q

What is the most important organism to consider in osteomyelitis?

A

Staph aureus

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18
Q

What are the six main classifications of osteomyelitis?

A
  1. Open fractures
  2. Diabetes/vascular insufficiency
  3. Haematogenous osteomyelitis
  4. Vertebral osteomyelitis
  5. Prosthetic joint infection
  6. Specific hosts and pathogens
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19
Q

What is the clinical clue for osteomyelitis following open wound fracture?

A

Non-union and poor wound healing

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20
Q

Diabetes/vascular insufficiency OM

Is this mostly contiguous or haematogenous?

A

Contiguous

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21
Q

If a diabetic foot ulcer has been there for >2 months and is >2 cm in diameter, what should you consider?

A

Osteomyelitis

22
Q

Classic investigation for osteomyelitis?

A

Investigation - probe to bone (60% sensitive, 90% specific) -> good at ruling in osteomyelitis, but quite gruesome. If you can see a tendon or bone just from looking, then it is osteomyelitis.

23
Q

What is the general rule for antibiotic treatment of OM?

What are the two exceptions?

A

Always try and withhold empiric therapy – you want to try and find the bug first before you treat. This is because it is a chronic, indolent thing, and people don’t tend to die of it.
Exceptions
1. Sepsis -> in this case you must treat empirically straight away
2. If they have a lot of skin and soft tissue involvement e.g. angry cellulitis, you don’t have time to wait for biopsy etc so you must start treatment then.

24
Q

What is the main antibiotic of choice in OM?

A

Acute – flucloxacillin (covers Staph aureus, staph epi, Streptococci); if they are known to have MRSA then think about vancomycin

25
Q

What is the classic scenario for haematogenous OM?

What is the causative organism?

A

Tennis shoe on, step on a nail

Pseudomonas

26
Q

Which groups is haematogenous OM common in?

A

Prepubertal children
People who inject drugs (PWID)
Central lines, dialysis, elderly

27
Q

Which sites does OM affect in PWID?

What are the most common causative organisms?

A 
Unusual sites
- Sternoclavicular joint
- Sternocostal joints
- Sacroiliac joint
- Pubic symphsis
Staph and strep
28
Q

What is the causative organism in needle lickers?

A

Eikenella corrodens

29
Q

What happens if you mismanage staph aureus?

A

It will seed and grow elsewhere. If you have staph aureus in a blood culture, and a line in the patient, then remove the line if possible. Then do blood cultures again and if it’s still negative, then do other investigations. Treatment for staph aureus -> flucloxacillin and drainage.

30
Q

What are two unsual sites should you be aware of in OM?

A
  1. Osteitis pubis (at pubic symphysis)
    - Urogynae procedures predispose to bacterial causes
    - Aseptic oseitis pubis – triggered by surgery, can be up to 28 months later; athletes can get it
  2. Clavicle osteo
    - Risk factors - neck surgery, subclavian vein catheterization
31
Q 
What are SAPHO and CRMO? 
What are they characterized re history?
General symptoms?
What type of lesions?
Sites?
A

Synovitis Acne Pustolosis Hyperostosis Osteitis (adults)
Chronic Recurrent Multifocal Osteomyelitis (kids)
History of recurrence plus culture samples are crucial to exclude osteomyelitis
Lesions are multifocal
Sites – 63% chest wall, 40% pelvis, 33% spine, 6% lower limb
Patients tend to have five or so active lesions at a time

32
Q

What are some ways of getting vertebral osteomyelitis?

A

Mostly haematogenous and may be associated with an epidural abscess or psoas abscess

33
Q

What are some risk factors for vertebral osteomyelitis?

A 
PWID
IV site infections 
GU infections 
SSTI
Post-operative
34
Q

What are some common symptoms and signs of vertebral osteomyelitis?

A 
50% have fever 
90% insidious pain and tenderness
15% neurological signs/symptoms 
90% raised inflammatory markers 
Less than 50% have raised white cell count
35
Q

Investigation for vertebral OM?

A

First biopsy – 38-60% yield
Second biopsy has 80% sensitivity
If still no answer then consider open biopsy

36
Q

Treatment of vertebral osteomyelitis?
Length of antimicrobial therapy?
What should you expect on blood when starting treatment?
Why would an MRI be repeated?

A

Drainage of large paravertebral/epidural abscesses
Antimicrobials for 6 weeks
Expect >50% increase in ESR within a month of starting treatment
MRI repeated only if unexplained increase in inflammatory markers; increasing pain; new anatomically related signs or symptoms

37
Q 
Vertebral TB
Aka?
Systemic symptoms?
What type of associated infection?
What fraction have pulmonary TB?
What additional tests should you do in adults vs children?
A

Called Pott’s disease
Often NO systemic symptoms
½ have associated skin and soft tissue infection
Less than half have pulmonary TB
In adults always offer a HIV test
In kids, check for reduced receptors for IFN-gamma R1, IL12 beta 1

38
Q

PVL producing staph aureus in prosthetic joint infection
What is PVL?
When should you be suspicious of this?

A

Panton Valentine Leukocidin = toxin Be suspicious if someone is disproportionately unwell
If you supply the lab with information saying that you suspect this, then it will do a PCR for the genetics which encode this toxin

39
Q

What is the classical triad of symptoms for PVL producing staph aureus

A

Severe skin infections
Necrotizing pneumonia
Invasive infections e.g. bacteraemia, septic arthritis

40
Q

Define planktonic vs sessile bacteria

A 
Planktonic bacteria (aka in free existence) – bacteraemia
Sessile bacteria (aka you have staph aureus in the blood stream) -> gets to joint -> by the time it gets there its phenotype and behaviour has changed, so your approach has to be different at the joint) – form a community of bacteria with a biofilm around it and an extracellular matrix. This is why prosthetic joint infection is so hard to treat and so recurrent.
41
Q

What is the most important antibiotic for biofilm activity?

Disadvantages of this antibiotic?

A

The most important antibiotic for biofilm activity is rifampicin (if bacteria is sensitive to it) – but it has complications as it has a huge number of interactions, and can be hepatotoxic. Resistance to rifampicin is a point mutation – if you give rifampicin on its own then you will get resistance so you need to give it with other antimicrobials.

42
Q

Why is diagnosis of prosthetic joint infection tricky?

What can you do to try and confirm a specific pathogen?

A

Diagnosis can be difficult because the organisms which cause this type of infection are common skin commensals. Culture perioperative tissue samples – if same organism grows from multiple samples then your suspicion of that organism should be raised.

43
Q

Which three things can all present with inflammation and swelling around a joint?

A

Synovitis
Cellulitis
Osteomyelitis

44
Q

Treatment of septic arthritis?

A

Presumptive treatment to cover Staphylococcus aureus - FLUCLOXACILLIN (high doses)
Less than 5 years old add Ceftriaxone (for H influenzae cover)
Adjust when organisms confirmed
First you sample, then give treatment for what you think it will be, then when you get results back adjust your treatment to specific bug.

45
Q

What organism should you expect in knee bursitis?

How should you treat this?

A

Staph aureus

Flucloxacillin

46
Q

Flucloxacilin doesn’t work for MRSA; which antibiotic does?

A

Vancomycin

47
Q

Which STI should you not forget about in infected arthritis?

A

Gonorrhoea

48
Q

What is the classic presentation of Lyme arthritis?

A

Asymmetrical huge joint swelling that isn’t as painful as it looks

49
Q

What is pyomyositis?
How is it treated?
Most common infecting organism?
Who gets it in temperate regions and which bug is causing it in these patients?

A

Infection of muscle by bacteria
Surgical emergency - cut wide and deep
90% staphylococcus Temperate – immunosuppressed (Pseudomonas, beta haemolytic strep, enterococcus)

50
Q

What is the infecting organism in tetanus?
What does it produce?
What does this cause?
How does it do this?
What is the intubation period?
Where should you put any patient in whom you suspect tetanus?
Treatment for pyomyositis caused by this?

A

Clostridium tetani
A neurotoxin which causes spastic paralysis
Binds to inhibitory neurones, preventing release of neurotransmitters
4 days - several weeks
If you suspect tetanus, the patient may have mild symptoms, but they must be in ICU regardless, as any stimulation can cause tetanii of the diaphragm and spastic paralysis.
Treatment - surgical debridement, antitoxin, antibiotics (penicilin, metronidazole)

51
Q

What is myositis?

A

Infection of muscle by something other than bacteria - can be viral, protozoal, fungal

52
Q

What is a Brodie’s abscess?

A

Subacute osteomyelitis in children where the bone reacts by walling off the abscess with a thin rim of sclerotic bone

MSK (19 decks)

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