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Infection Systems > Lecture 12: Skin and Soft Tissue > Flashcards

Lecture 12: Skin and Soft Tissue Flashcards

1
Q

what is impetigo?

A
  • superficial skin infection
  • multiple vesicular lesions on an erythematous base
  • golden crust is highly suggestive of this diagnosis
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2
Q

what organisms cause impetigo?

A
  • most commonly due to staph. aureus
  • less commonly strep. pyogenes
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3
Q

impetigo treatment

A
  • small areas can be treated with topical antibiotics alone
  • large areas need topical treatment and oral antibiotics (e.g. flucloxacillin)
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4
Q

clinical presentation of Erysipelas

A
  • infection of the upper dermis
  • painful, red area (no central clearing)
  • associated fever
  • regional lymphadenopathy and lymphangitis
  • typically has distinct elevated borders
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5
Q

Erysipelas is most commonly due to which organism?

A

Strep pyogenes

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6
Q

Cellulitis clinical presentation

A
  • diffuse skin infection involving deep dermis and subcutaneous fat
  • presents as spreading erythematous area with no distinct borders
  • fever is common
  • regional lymphadenopathy and lymphangitis
  • possible source of bacteraemia
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7
Q

most likely organisms causing cellulitis are?

A

strep pyogenes
staph aureus

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8
Q

which predisposing factors can increase risk of cellulitis?

A
  • diabetes mellitus
  • tinea pedis
  • lymphoedema
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9
Q

what is the treatmnt for Erysipelas and Cellulitis?

A
  • a combo of anti-staphylococcal and anti-streptococcal antibiotics
  • in extensive disease, admission for intravenous antibiotics and rest
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10
Q

list some hair-associated infections

A
  • folliculitis
  • furunculosis
  • carbuncles
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11
Q

clinical presentation of folliculitis

A
  • circumscribed, pustular infection of a hair follice
  • up to 5mm in diameter
  • presents as small red papules
  • central area of purulence that may rupture and drain
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12
Q

most common organism causing folliculitis?

A
  • staph aureus
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13
Q

clinical presentation of furunculosis

A
  • commonly referred to as boils
  • single hair follice-associated inflammatory nodule extending into dermis and subcutaenous tissue
  • usually affected moist, hair, friction-prone areas of body (face, axilla, neck and buttocks)
  • may spontaneously drain purulent material
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14
Q

most common organism causing furunculosis?

A

stap aureus

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15
Q

furunculosis risk factors

A
  • obesity
  • diabetes mellitus
  • CKD
  • corticosteroid use
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16
Q

Carbuncle clinical presentation

A
  • occurs when infection extends to involve multiple furuncles
  • often located back of neck, posterior trunk or thigh
  • multiseptated abscesses
  • purulent material may be expressed from multiple sites
  • constitutional symptoms present
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17
Q

treatment of folliculitis, furunculosis and carbuncles?

A
  • folliculitis: no treatment or topical abx
  • furunculosis: no treatment or topical abx. If not improving oral abx may be necessary.
  • carbuncles: often require hospital admission, surgery and IV abx
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18
Q

necrotising fasciitis risk factors

A
  • diabetes mellitus
  • surgery
  • trauma
  • peripheral vascular disease
  • skin popping
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19
Q

what does type I necrotising fasciitis refer to?

A

a mixed aerobic and anaerobic infection (diabetic foot infection, Fournier’s gangrene)

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20
Q

necrotising fasciitis typical organisms

A
  • streptococci
  • staphylococci
  • enterococci
  • gram-negative bacilli
  • clostridium
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21
Q

what does type II necrotising fasciitis refer to?

A

a monomicrobial infection normally associated with strep pyogenes

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22
Q

necrotising fasciitis clinical presentation

A
  • rapid onset
  • sequential development of erythema, extensive oedema and severe, unremitting pain
  • haemorrhagic bullae, skin necrosis and crepitus may develop
  • systemic features: fever, hypotension, tachycardia, delirium and multi-organ failure
  • anaesthesia at site of infection is highly suggestive of this disease
23
Q

necrotising fasciitis management

A
  • surgical review is mandatory
  • imaging may help but could delay treatment
  • abx should be broad-spectrum: flucloxacillin, gentamicin, clindamycin
24
Q

pyomyositis clinical presentation

A
  • purulent infection deep within striated muscle, often manifesting as an abscess
  • infection is often secondary to seeding into damaged muscle
  • can present with fever, pain and woody induration of affected muscle
  • if untreated can lead to septic shock and death
25
Q

pyomyositis predisposing factors

a rare and treatable bacterial infection that affects skeletal muscles

A
  • diabetes mellitus
  • HIV/immunocompromised
  • IV drug use
  • rheumatological diseases
  • malignancy
  • liver cirrhosis
26
Q

pyomyositis causative organisms

A
  • commonest is staph aureus
  • other organisms can be involved including gram positive/negatives, TB and fungi
27
Q

pyomyositis investigation

A

CT/MRI

28
Q

pyomyositis treatment

A
  • drainage with antibiotic cover depending on gram stain and culture results
29
Q

what are bursae?

A
  • small sac-like cavities that contain fluid and are lined by synovial membrane
  • located subcutaneously between bony prominences or tendons
  • facilitate movement with reduced friction
  • most common include patellar and olecranon
30
Q

septic bursitis clinical presentation

A
  • infection of bursae often from adjacent skin infection
  • peribursal cellulitis, swelling and warmth are common
  • fever and pain on movement also seen
  • diagnosis is based on aspiration of the fluid
31
Q

septic bursitis predisposing factors

A
  • adjacent skin infection
  • rheumatoid arthritis
  • alcoholism
  • diabetes mellitus
  • IV drug abuse
  • immunosuppression
  • renal insufficiency
32
Q

most common causative organism of septic bursitis?

A

staph aureus infection
rare organisms include: gram-negative, mycobacteria, brucella

33
Q

what is infectious tenosynovitis?

A
  • infection of the synovial sheets that surround tendons
  • flexor-muscle associated tendons and tendon sheats of the hand most commonly involved
34
Q

most common organisms causing infectious tenosynovitis?

A
  • staph aureus and streptococci
  • chronic infections may be due to mycobacteria, fungi
35
Q

how does infectious tenosynovitis commonly present?

A
  • present with erythematous fusiform swelling of finger
  • held in a semiflexed position
  • tenderness over the length of the tendon sheat and pain with extension of finger are classical
36
Q

infectious tenosynovitis treatment

A
  • empiric antibiotics
  • hand surgeon to review ASAP
37
Q

pathogenesis of toxin-mediated syndromes

most often due to super antigens, what does it cause?

A
  • often due to superantigens
  • group of pyrogenic exotoxins
  • do not activate immune system via normal contact between APC and T cells, instead, superantigens bypass this and attach directly to the T cell receptors activating up to 20% of the total pool of T cells.
  • causes massive burst in cytokine release
  • leads to endothelial leakage, haemodynamic shock, multi-organ failure and death.
38
Q

what toxins does staph aureus release?

A

TSST1
ETA and ETB

39
Q

what toxin does strep pyogenes release?

A

TSST1

40
Q

what is the diagnostic criteria for staphylococcal toxic shock syndrome?

A
  • fever
  • hypotension
  • diffuse macular rash
  • three of the following organs involved: liver, blood, renal, GI, CNS, muscular
  • isolation of staph aureus from mucosal or normally sterile sites
  • production of TSST1 by isolate
  • development of antibody to toxin during convalescence
41
Q

describe streptococcal TSS

cause, mortality rate, treatment

A
  • almost always associated with presence of streptococci in deap seated infections such as erysipelas or necrotising fasciitis.
  • mortality rate much higher than staph 50% vs 5%
  • need urgent surgical debridement of the infected tissues
42
Q

what is the treatment for TSS?

A
  • remove offending agent e.g. tampon
  • IV fluids
  • inotroped
  • antibiotics
  • IV immunoglobulins
43
Q

what is staphylococcal scalded skin syndrome and how does it present?

A
  • infection due to a particular strain of staph aureus producing the exfoliative toxin A or B
  • characterised by widespread bullae and skin exfoliation
  • usually occurs in children but rarely in adults as well
44
Q

staphylococcal scalded skin syndrome treatment

A

IV fluids
antimicrobials

45
Q

what can panton-valentine leucocidin toxin cause?

A

SSTI
haemorrhagic pneumonia

46
Q

IV catheter associated infections clinical presentation

A
  • nosocomial infection
  • normally starts as local SST inflammation progressing to cellulitis and even tissue necrosis
  • common to have an associated bacteraemia
47
Q

risk factors for IV-catheter associated infections

A
  • continuous infusion > 24 hours
  • cannula in situ > 72 hours
  • cannula in lower limb
  • patients with neurological/neurosurgical problems
48
Q

most common causative organism for IV catheter associated infections?

A

staph aureus (MSSA and MRSA)

49
Q

IV/catheter associated infections treatment

A
  • treatment is to remove cannula
  • express any pus from the thrombophlebitis
  • antibiotics for 14 days
  • echocardiogram
50
Q

classification of surgical wounds from I to IV

A
  • class 1: clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
  • class 2: clean-contaminated wound (above tracts entered but no unusual contamination)
  • class 3: contaminated wound (open, fresh accidental wounds or gross spillage from GI tract)
  • class 4: infected wound (existing clinical infection, infection present before the operation)
51
Q

list the causative organisms of surgical site infections

A
  • staph aureus (incl. MSSA and MRSA)
  • coagulase negative staphylococci
  • enterococcus
  • E.coli
  • pseudomonas aeruginosa
  • enterobacter
  • streptococci
  • fungi
  • anaerobes
52
Q

patient-associated risk factors for surgical site infections

A
  • diabetes
  • smoking
  • obesity
  • malnutrition
  • concurrent steroid use
  • colonisation with staph aureus
53
Q

procedural risk factors associated with surgical site infections

A
  • shaving of site night prior to procedure
  • improper preoperative skin prep
  • improper antimicrobial prophylaxis
  • break in sterile technique
  • inadequate theatre ventilation
  • perioperative hypoxia
54
Q

SSTIs that need urgent attention

A
  • necrotising fasciitis
  • pyomyositis
  • toxic shock syndrome
  • PVL infections
  • venflon-associated infections

Infection Systems (13 decks)

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