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Flashcards in Skin and Soft Tissue Infections Deck (71)
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1
Q

What are the infections associated with the following depth of skin?

A
2
Q

What are the causative organisms for impetigo, erysipelas, cellulitis and necrotising fascitis?

A

Impetigo - s. aureus (less commonly due to strep pyogenes)

Erysipelas - strep pyogens

Cellulitis - Strep pyogenes, staph aureus (uncommon), H. influenza (rare)

Necrotising fascitis (strep pyogenes or mixed bowel flora)

3
Q

What are the signs of impetigo?

A

Superficial skin infection, multiple vascular lesions on an erythematous base

Golden crust is highly suggestive of this diagnosis

4
Q

Which age group is impetigo common in?

A

Age 2-5 years of age

5
Q

Where does impetigo normally occur?

A

Usually occurs on exposed parts of the body including face, extremities and scalp

6
Q

What are predisposing factors for impetigo?

A

–Skin abrasions

–Minor trauma

–Burns

–Poor hygiene

–Insect bites

–Chickenpox

–Eczema

–Atopic dermatitis

7
Q

What is the treatment for impetigo?

A

Small areas can be treated with topical antibiotics alone

Large areas need topical treatment and oral antibiotics (flucloxacillin)

8
Q

Where does erysipelas affect?

A

Affects the upper dermis

9
Q

What are the other features of erysipelas besides infeciton of the upper dermis?

A

Painful, red area (no central clearing)

Associated fever

Regional lymphadenopathy and lymphangitis

Typically has distinct elevated borders

Most commonly due to strep pyogenes

10
Q

Where is erysipelas likely to occur?

A

Most cases involve the lower limbs (70-80%)

5-20% affect the face

  • Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus
  • May involve intact skin
  • High recurrence rate (30% within 3 years)
11
Q

What layerof the skin does cellulitis affect?

A

It is a diffuse skin infection involving deep dermis and subcutaneous fat

12
Q

How does cellulitis differ from erysipelas?

A

Cellulitis has no distinct elevated borders

13
Q

What is the most likely causative organism for cellulitis?

A

Strep pyogenes and staph aureus

14
Q

What are the symptoms that can occur in conjunction with cellulitis?

A

Fever

Regional lymphadenopthy and lymphangitis

Possible source of bacteraemia

15
Q

What re the predisposing factors for cellulitis?

A

Diabetes mellitus

Tinea pedis

Lymphoedema

Patients can have lymphangitis and/or lymphadenitits

16
Q

What is the treatment for erysipelas and celulitis?

A
  • A combination of anti-staphylococcal and anti-streptococcal antibiotics
  • In extensive disease, admission for intravenous antibiotics and rest
17
Q

What are the hair assocaited infections?

A
  • Folliculitis
  • Furunculosis
  • Carbuncles
18
Q

What is the difference between folliculitis, furuncles and carbuncles?

A

Folliculitis - erythema and a psutule in a single follicle

Furuncle - red tender nodule surrounding a follicle with one draining point

Carbuncle - abscess of several follciels with several drainage points

19
Q

Describe the appearance of folliculitis

A

Small red papules

Central area of purulence that may rupture and drain

Up to 5 mm in diameter

20
Q

What is the most common organism for folliculitis?

A

Staph aureus

It is a benign condition, constitutional symptoms not often seen

21
Q

What tissue layer does furunculosis spread into?

A

Extends into the dermis and subcutaneous tissue

22
Q

Where does furunculosis usualy affect?

A

•Usually affected moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)

23
Q

What is the most common organism that can cause furunculosis?

A

Staph aureus is the most common organism

24
Q

What are the risk factors for furunculosis?

A

–Obesity

–Diabetes mellitus

–Atopic dermatitis

–Chronic kidney disease

–Corticosteroid use

25
Q

How are carbuncles formed?

A

When infection extends to involve multiple furuncles

26
Q

Where are carbuncles found?

A

•Often located back of neck, posterior trunk or thigh

27
Q

Describe the abscess found in a carbuncle

A

Multi-septated abscess

28
Q

What is the treatment of hair associated infections?

A

Folliculitis - no treatment or topical antibiotics

Furunculosis - no treatment or topical antibiotics, if not improving oral antibiotics might be necessary

Carbuncles often require admission to hospital, surgery and intravenous antibiotics.

29
Q

What are the predisposing factors to necrotising fasciitis?

A

•Predisposing conditions include

–Diabetes mellitus (diabetic foot infection is type 1)

–Surgery

–Trauma

–Peripheral vascular disease

–Skin popping

30
Q

What is the difference between type 1 and type 2 necrotising fasciitis?

A

Type 1 - mixed infection (aerobic and anaerobic)

Type 2 - monomicrobial

31
Q

What are the bacteria assocaited with necrotising fasciitis?

A

Typical organisms for type 1 include:

–Streptococci

–Staphylococci

–Enterococci

–Gram negative bacilli

–Clostridium

Type 2:

Strep pyogenes

32
Q

What are the features of necrotising fasciitis?

A
  • Rapid onset
  • Sequential development of erythema, extensive oedema and severe, unremitting pain
  • Haemorrhagic bullae, skin necrosis and crepitus may develop
  • Systemic features include fever, hypotension, tachycardia, delirium and multiorgan failure
  • Anaesthesia at site of infection is highly suggestive of this disease
33
Q

What is the management of necrotising fasciitis?

A
  • Imaging may help but could delay treatment
  • Antibiotics should be broad spectrum

–Flucloxacillin

–Gentamicin

–Clindamycin

•Overall mortality ranges between 17-40%

34
Q

What is pyomyositis?

A

Purulent infection deep within striated muscle, often manifesting as an abscess

Infection is often secondary to seeding into damaged muscle

35
Q

What are the common sites of pyomyositis?

A

–Thigh

–Calf

–Arms

–Gluteal region

–Chest wall

–Psoas muscle

36
Q

What is the clinical presentation for pyomyositis?

A

Can present with fever, pain and woody induration of affected muscle

37
Q

What are the risks of pyomyositis?

A

Can lead to septic shock and death

38
Q

What are predisposing factors for pyomyositis?

A

–Diabetes mellitus

–HIV/immunocompromised

–Intravenous drug use

–Rheumatological diseases

–Malignancy

–Liver cirrhosis

39
Q

What are the causative organisms for pyomyositis?

A

Commonest cause is staph aureus, other organisms can be involved including gram positive/negatives, TB and fungi

40
Q

What are the relevant investigations for pyomyositis?

A

Investigation using CT/MRI

41
Q

What is the treatment for pyomyositis?

A

•Treatment is drainage with antibiotic cover depending on Gram stain and culture results

42
Q

Where does septic bursisits most commonly occur?

A

Most commonly occurs in the patella and the olecranon

43
Q

What are the predisposing factors for septic bursitis?

A
  • Infection is often from adjacent skin infection
  • Other predisposing factors include

–Rheumatoid arthritis

–Alcoholism

–Diabetes mellitus

–Intravenous drug abuse

–Immunosuppression

–Renal insufficiency

44
Q

What are the clinical features of septic bursitis?

A
  • Peribursal cellulitis, swelling and warmth are common
  • Fever and pain on movement also seen
  • Diagnosis is based on aspiration of the fluid
45
Q

What are the infective organisms for septic bursitits?

A

Staph aureus

•Rarer organisms include

–Gram negatives

–Mycobacteria

–Brucella

46
Q

What is infectious tenosynovitis?

A

Infection of the synovial sheaths that surround tendons

47
Q

What are the most commonly associated tendons in infectious tenosynovitis?

A

•Flexor muscle-associated tendons and tendon sheats of the hand most commonly involved

48
Q

What is the most common inciting agent for infectious tenosynovitis?

A

Penetrating trauma

49
Q

What are the causative organisms for infectious tenosynovitis?

A
  • Most common cause Staph aureus and streptococci
  • Chronic infections due to mycobacteria, fungi
  • Possibility of disseminated gonococcal infection
50
Q

What are the clinical features of infectious tenosynovitis?

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
51
Q

What is the treatment for infectious tenosynovitis?

A
  • Empiric antibiotics
  • Hand surgeon to review ASAP
52
Q

What is the effect of superantigens on the immune system?

A
  • Group of pyrogenic exotoxins
  • Do not activate immune system via normal contact between APC and T cells
  • Superantigens bypass this and attach directly to the T cell receptors activating up to 20% of the total pool of T cells instead of the normal 1/10,000
  • Massive burst in cytokine release
  • Leads to endothelial leakage, haemodynamic shock, multi-organ failure and ?death
53
Q

What are the most likely causative organisms for toxin mediated syndromes?

A
  • Mostly due to some strains of Staphylococcus aureus and Streptococcus pyogenes
  • Staph aureus: TSST1 (this can cause toxic shock syndrome)

ETA and ETB

•Strep pyogenes: TSST1

54
Q

What are the diagnostic criteria for toxic shock syndrome?

A
  • Fever
  • Hypotension
  • Diffuse macular rash
  • Three of the following organs involved
  • Liver, blood, renal, gatrointestinal, CNS, muscular
  • Isolation of Staph aureus from mucosal or normally sterile sites
  • Production of TSST1 by isolate
  • Development of antibody to toxin during convalescence
55
Q

What often lies in conjunction with streptococcal toxic shock syndrome?

A

•Almost always associated with presence of Streptococci in deep seated infections such as erysipelas or necrotising fasciitis

56
Q

What is mortality rate of Strep TSS?

A

•Mortality rate is much higher than Staphylococcal (50% vs 5%)

57
Q

What is treatment of TSS?

A
  • Remove offending agent (ex tampon) - high absorbency tampons are assocaited with toxic shock syndromes - increased in 1980’s
  • Intravenous fluids
  • Inotropes (these alter the strength of musclular contractions)
  • Antibiotics
  • Intravenous immunoglobulins

Strepp TSS requires immediate debridement of the infected tissues

58
Q

What causes staphylococcal scalded skin syndrome?

A

•Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B

Exfoliation is the removal of the dead skin cells on the skins outermost surface

Exfoliative toxin is called exfoliatin - Exfoliatin breaks down desmosomes. Specifically it is a proteas that cleave desmoglein -1 which normally holds in place the granulosum and the spinosum

59
Q

What are the clinical features of staphylococcal scalded skin syndrome?

A

Characterised by widerspread bullae and skin exfoliation

Usually occurs in children but rareyl in adults as well

60
Q

What are the features of panton-valentine leucocidin toxin?

A

Can causes SSTI (skin and soft tissue infection as well as haemorrhagic pneumonia)

  • Tends to affect children and young adults
  • Patients present with recurrent boils which are difficult to treat
61
Q

Describe panton-velantine leucocidin toxin

A

Gamma haemolysin

62
Q

What is the treatment for panton-valentine leucocidin toxin

A

•Treat with antibiotics that reduce toxin production

63
Q

What are the stages of progression for intravenous - catheter associated infections?

A

Normally starts as inflammation

Then cellulitits

Then tissue necrosis

Common to have associated bacteraemia

64
Q

What are the risk factors for intravenous catheter infections?

A

Continuous infusion (over 24 hours)

Cannula in situ (over 72 hours)

Cannula in situ lower limb

Patients with neurological/neurosurgical problems

65
Q

What are the intravenous- catheter associated infections?

A

Most common organism is staph aureus (MSSA and MRSA)

Commonly forms biofilm which then spills into the blood stream

Can seed into other places such as endocarditis, osteomyelitis

Diagnosis made clinically or by positive blood cultures

66
Q

What is the treatment for intravenous associated infections?

A

Remove cannula

Express any pus from the thrombophlebitis

Antibiotics for 14 days echocardiogram

Prevention is more important:

–Do not leave unused cannula

–Do not insert cannulae unless you are using them

–Change cannulae every 72 hours

–Monitor for thrombophlebitis

–Use aseptic technique when inserting cannulae

67
Q

What are the classes of surgical wounds?

A
  • Class I: Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
  • Class II: Clean-contaminated wound (above tracts entered but no unusual contamination)
  • Class III: Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
  • Class IV: Infected wound (existing clinical infection, infection present before the operation)
68
Q

What are the causes of surgical site infections?

A
  • Staph aureus (incl MSSA and MRSA)
  • Coagulase negative Staphylococci
  • Enterococcus
  • Escherichia coli
  • Pseudomonas aeruginosa
  • Enterobacter
  • Streptococci
  • Fungi
  • Anaerobes
69
Q

What are risk fctors for surgical site infections?

A

•Patient associated

–Diabetes

–Smoking

–Obesity

–Malnutrition

–Concurrent steroid use

–Colonisation with Staph aureus

Procedural:

–Shaving of site the night prior to procedure

–Improper preoperative skin preparation

–Improper antimicrobial prophylaxis

–Break in sterile technique

–Inadequate theatre ventilation

–Perioperative hypoxia

70
Q

What is the diagnosis of surgical site infections?

A
  • Importance of sending pus/infected tissue for cultures especially with clean wound infections
  • Avoid superficial swabs – aim for deep structures
  • Consider an unlikely pathogen as a cause if obtained from a sterile site (ex bone infection)
  • Antibiotics to target likely organisms

(so culture, use deep sites, sterile site = unlikely pathogen, antibiotics)

71
Q

What are the infections that need urgent attention?

A

–Necrotising fasciitis

–Pyomyositis

–Toxic shock syndrome

–PVL infections

–Venflon-associated infections