Soft tissue, bone and joint infections Flashcards

1
Q

What is the aim of the skin and what are its 3 main layers?

A

physical barrier against microorganisms
3 layers:
1) epidermis: outer layer and waterproof
2) dermis: tough connective tissue, hair follicles and sweat glands
3) subcutaneous layer: fat and connective tissue

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2
Q

What are the non-specific defences of skin?

A

exfoliation: sloughing of the stratum corneum dislodges many adherent bacteria
dryness: bacterial counts much higher in moist areas
acidic: pH 5.5
low temperature
sweat glands: saltiness - inhibits bacteria
normal bacterial flora - complete for colonisation sites, compete for nutrients

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3
Q

What is the normal flora of the skin?

A

microorganisms are always present on the skin

  • s epidermidis
  • s aureus
  • micrococci
  • diphtheroids

some microorganisms are transient flora and are prevented from colonising due to:

  • mechanical barrier
  • sebum
  • cleaning and washing
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4
Q

What type of organism is staphylococcus aureus?

A
gram +ve cocci and coagulase positive 
golden colonies - yellowy/cream colour 
30-40% of population are colonised 
acquired resistance to beta-lactam antibiotics - methicillin 
causes haemolysis of red cells
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5
Q

What type of organism is streptococcus pyogenes?

A

group A streptococci
gram +ve cocci
beta haemolytic - get partial haemolysis of alpha chains
colonises the pharynx

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6
Q

What syndromes do you get within the epidermidis and dermis?

A
impetigo 
folliculitis
furunculosis 
carbunculosis 
erysipelas
\+ cellulitis
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7
Q

What syndromes do you get within the superficial fascia, subcutaneous fat, nerves, arteries, veins and deep fascia ?

A

necrotising fascitis

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8
Q

What syndrome do you get in the muscle?

A

myonecrosis

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9
Q

What conditions predispose to skin invasion?

A

excessive moisture - induces breakdown of the stratum corneum - occlusive dressings, obesity (infections seen in intertriginous folds)
minor abrasions
surgery
crush injuries - RTAs
burns - infections primary cause of death in burns patients
percutaneous e.g. intravenous catheters
bed sores- cutaneous lesions due to pressure lead to skin necrosis and secondary infections
conditions that compromise the blood supply- diabetes

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10
Q

What is impetigo?

A
superficial skin infection 
friable golden crusts over erythematous skin 
more common in children 
very contagious
usually due to strep A
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11
Q

What is folliculitis?

A

infection of the hair follicles
common sites are groin and scalp
causative organism= s aureus
tx= flucloxacillin

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12
Q

What are some pyogenic skin infections?

A

furunculosis = deep inflammatory lesion progressing from a folliculitis
carbuncle = multiple fistulas = extend into the subcutaneous layer, multiple abscesses develop, separated by connective tissue
acute paronchia = skin infection arising from nail - remove nail and pus pores out

tx= oral flucloxacillin

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13
Q

What is cellulitis?

A

acute, spreading inflammation of the lower dermis and associated with subcutaneous layer of skin
diffuse inflammation without necrosis or localisation of pus
often seen as red halo around wound
skin is hot, red and painful

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14
Q

What is the causative agent of cellulitis commonly ?

A

s. aureus

less common- s pyogenes, c perfringens

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15
Q

How is cellulitis diagnosed?

A

most commonly affects lower extremities
acute, tender, erythematous and swollen area of skin - could be a DVT
fever and malaise
WCC and CRP usually raised
blood cultures only useful if pt is septic

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16
Q

What is the treatment for cellulitis?

A

rest and elevation
mark area of cellulitis
oral penicillin V and flucloxacillin
if severe may need IV abx

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17
Q

What is erysipelas?

A

infection involving the upper dermis and extends into the superficial cutaneous lymphatics
distinguished clinically by lesions raised above surrounding skin, clear line of demarcation of involved and not involved tissue
Group streptococci A most common cause
most common on legs or face
diagnosis: clinical appearance
treatment: penicillin

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18
Q

What is staphylococcal scalded skin syndrome?

A

seen in infants, young children and immunocompromised
clinical:
- starts with erythema, then fever, followed by large fluid filled bullae (large blister containing serous fluid), rupture and causes widespread exfoliation

toxins released into blood from localised S aureus infection - can die from this

Treatment: flucloxacillin

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19
Q

What do you worry that cellulitis might progress to?

A

necrotising fasciitis

20
Q

What is necrotising fasciitis?

A

can be caused by one organism on its own (group A strept) or combination of bacteria
enter fascial plane following trauma, surgery or occult bacteraemia
inflammatory response - affects neurovascular bundles
thrombosis of vessels compromises blood supply and nerves to the skin

21
Q

What are the 3 stages of symptoms in necrotising fasciitis?

A

1) early (<24 hours)
- presence of skin trauma but pain seems disproportionate to injury
- flu like symptoms and thirst
2) advanced symptoms
- swelling of painful area
- large dark blotches (violet)
- mottled flaky appearance at trauma site
3) critical symptoms
- severe fall in BP
- toxic shock from poisons released by bacteria
- unconsciousness

TX= IV abx and surgery

22
Q

What is gas gangrene?

A

very rare - common cause of death in the past military conflicts - arising in devitalised wounds contaminated with soil
clostridium perfringens - most common cause - produces toxin which causes cell death
can occur in synergistic soft tissue infections e.g. wound contaminated with coliforms - use up oxygen making it amenable for anaerobes to grow
Tx= urgent surgery to remove dead tissue

23
Q

Which patients is gas gangrene more common in ?

A

underlying blood vessel disease, diabetes or colon cancer

24
Q

What are surgical site infections?

A

infections that affect the surgical wound or deeper tissues handled during the procedure resulting in local signs and clinical symptoms

up to 20% of all healthcare associated (nosocomial) infections - >5% of patients who undergo surgery develop an SSI

associated with morbidity, extended hospital stay and financial burden to patients and healthcare system
majority are preventable

25
What is the actual definition of SSI?
incisional (superficial or deep) organ/space infection - has to occur within 30 days or 1 year if an implant was inserted Criteria 1) assessment of the surgical site (purulent drainage) 2) microbiology culture/s from sterile sites 3) signs of infection (fever, pain, tenderness, redness, heat)
26
What patient factors impact risk of SSI?
``` extremes of ages poor nutritional state obesity immunosuppression, diabetes, steroids smoking infections at other body sites ```
27
What microbial factors impact risk of SSI?
level of contamination (with prophylaxis) clean wound 5% clean contaminated 10% contaminated 20%
28
What procedural factors impact risk of SSI?
``` length of surgical scrub skin anti-sepsis pre-op shaving pre-op skin prep length of op operating theatre ventilation inadequate instrument sterilisation foreign material at surgical site ```
29
What pre-op measures can be in place to prevent SSI?
patient preparation (showering) hair removal (clippers) antibiotic prophylaxis staff preparation
30
What intra-op measures can be in place to prevent SSI?
operating team preparation patient skin preparation maintaining patient homeostasis wound dressings
31
What post-op measures can be in place to prevent SSI?
dressing and cleaning wound antibiotic treatment debridement specialist wound care services
32
What are the typical features of SSI?
``` Increased exudate increased swelling increased erythema increased pain increased local temperature peri-wound cellulitis - invasive infection, change in appearance of granulation tissue (discolouration, prone to bleed, highly friable) ```
33
What are the 2 major types of bone infections?
septic arthritis - infection of joint spaces, s. aureus, streptococci, gram negatives osteomyelitis - infection of bone - s.aureus, h. influenzae, e.coli, p.aeruginosa, proteus mirabilis
34
What are the different routes by which bacteria can enter a joint in septic arthritis?
haematogenous route= most important direct inoculation via trauma arthritis with associated tendonitis more common in a joint affected by rheumatoid disease or history of trauma bacteria in an occult bacteraemia enter joint space=>inflammatory response= invasion of neutrophils into the joint
35
What is acute osteomyelitis?
bone may become infected following direct introduction into the tissue by trauma/surgery or by haematogenous route chronic or acute infection
36
What are the clinical features of acute osteomyelitis in adults ?
``` severe pain reluctant to move fever, malaise backache history of UTI or urological procedure old, diabetic, immunocompromised ```
37
What are the clinical features of acute osteomyelitis in infants?
failure to thrive, drowsy, irritable metaphyseal tenderness decrease ROM commonest around knee
38
How do you diagnose osteomyelitis?
``` Hx and clinical exam FBC, ESR, CRP, Blood cultures XR US Bone scan MRI Aspiration ```
39
What is the treatment for osteomyelitis?
flucloxacillin - or clindamycin if penicillin allergic - or vancomycin if MRSA (+ fusidic acid or rifampicin if prothesis present or life-threatening condition) treat acute infection for 4-6 weeks treat chronic infection for at least 12 weeks
40
What do diabetic foot ulcers progress from?
cellulitis> deep soft tissue infection> osteomyelitis
41
What are the risk factors for diabetic foot infections?
vascular disease peripheral neuropathy poor foot care
42
What organisms usually cause diabetic foot infections?
s. aureus, beta-haemolyic streptococci, diphtheroids gram-ve bacilli (e.coli, k. pneumoniae, pseudomonas sp) anaerobes
43
What viruses can cause skin reactions?
herpes and vzv (chickenpox)- can persist in dorsal root ganglia and have potential to reactivate other viruses: rubella, parvovirus, measles, HSV6 HSV limited to genital and oral regions -
44
What are dermatophyte infections?
fungi invade dead tissues of the skin or its appendages (nails and hair) most common = trichophyton, epidermophyton and microsporum difficult to distinguish clinically spread from person to person or animal to person
45
How do you diagnose dermatophyte infections?
based on site tinea corporis = ringworm tinea pedia = athlete's foot tinea barbae = barber's itch
46
What is the treatment for dermatophyte infections?
topical imidazoles or other anti-fungal preparations e.g. nystatin, canestan, clotrimazole drug resistant strains or those with invasive life-threatening infections require triazole therapy (fluconazole)