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Skin and soft tissue infections Flashcards

1
Q

What things should be concidered when a patient has a skin or soft tissue infection?

A 
○ Site
- Possible complications with specific sites (ex; abdominal, face)
○ Organism
○ Host 
- Diabetes leading to neuropathy and vasculopathy
- Immunosuppression
- Renal failure
- Milroy’s disease
- Predisposing skin conditions (ex; atopic dermatitis) 
○ Environment
- Drug-resistant strains (MRSA)
- Drug interactions
- Drug allergies
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2
Q

What is impetigo?

A

○ Superficial skin infection
○ Multiple vesicular lesions on an erythematous base
○ Golden crust is highly suggestive of this diagnosis
- Forms on the face and arms of children
- Normally doesn’t give systemic effects
○ Most commonly due to Staph aureus
○ Less commonly Strep pyogenes
○ Common in children 2-5 years of age
○ Highly infectious
○ Usually occurs on exposed parts of the body including face, extremities and scalp

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3
Q

What are the predicposing factors of impetigo?

A
  • Skin abrasions
  • Minor trauma
  • Burns
  • Poor hygiene
  • Insect bites
  • Eczema
  • Atopic dermatitis
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4
Q

What is the treatment of impetigo?

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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5
Q

What is erysipealas

A

○ Infection of the upper dermis
○ May involve intact skin
○ High recurrence rate (30% within 3 years)

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6
Q

What are the clinical features of erysipealas?

A

○ Painful, red area (no central clearing)
○ Associated fever
○ Regional lymphadenopathy and lymphangitis
○ Typically has distinct elevated borders

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7
Q

What is the most comon cause of erysipealis?

A

Strep. pyogenes

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8
Q

Where does erysipealis occur?

A

○ 70-80% of cases involves the lower limbs
○ 5-20% affect the face
○ Tends to occur in areas of pre-existing lymphoedema, venous stasis, obesity, paraparesis, diabetes mellitus

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9
Q

What is cellulits?

A

Diffuse skin infection involving deep dermis and subcutaneous fat

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10
Q

What are the clinical features of cellulitis?

A

○ Presents as a spreading erythematous area with no distinct borders
○ Fever is common
○ Regional lymphadenopathy and lymphangitis
○ Possible source of bacteraemia
○ Patients can have lymphangitis and/or lymphadenitis

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11
Q

What are th predisposing factors of cellulitis

A
  • Diabetes mellitus
  • Tinea pedis
  • Lymphoedema
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12
Q

What causes cellulits?

A

○ Most likely organisms are Strep pyogenes and Staph aureus

○ Remember role of Gram negatives in diabetics and febrile neutropaenics

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13
Q

What is the treatment for erysipealis and cellulitis?

A

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

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14
Q

What is folliculitis?

A

○ Circumscribed, pustular infection of a hair follicle
○ Up to 5mm in diameter
○ Present as small red papules
○ Central area of purulence that may rupture and drain
○ Typically found on head, back, buttocks and extremities
○ It can infect adjuvant follicles if not treated
○ Benign condition
○ Constitutional symptoms not often seen

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15
Q

What is the most common cause of folliculitis ?

A

Staph aureus

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16
Q

What are furuncosis?

A

○ Furuncles commonly referred as boils
○ Single hair follicle-associated inflammatory nodule
○ Extending into dermis and subcutaneous tissue
○ Usually affected moist, hairy, friction-prone areas of body (face, axilla, neck, buttocks)
○ May spontaneously drain purulent material
○ Systemic symptoms uncommon

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17
Q

What is the most common cause of furuncosis?

A

Staph. aureus

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18
Q

What are the risk factors for furuncosis?

A
  • Obesity
  • Diabetes mellitus
  • Atopic dermatitis
  • Chronic kidney disease
  • Corticosteroid use
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19
Q

What is a carbuncle?

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 common
○ A normal healthy patient shouldn’t get this, so look for underlying causes

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20
Q

What is the treatment for hair associated infections?

A

○ With folliculitis, no treatment or topical antibiotics
○ With furunculosis, no treatment or topical antibiotics. If not improving oral antibiotics might be necessary
○ Carbuncles often require admission to hosiptal, surgery and intravenous antibiotics

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21
Q

What is necrotosing fasciitis?

A

○ One of the infectious diseases emergencies

○ Any site may be affected

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22
Q

What are the predisposing factors of necrotosing fasciitis?

A
  • Diabetes mellitus
  • Surgery
  • Trauma
  • Peripheral vascular disease
  • Skin popping
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23
Q

What is type 1 necrotosing fasciitis?

A

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

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24
Q

What are the typical organisms that cause type 1 necrotosing fasciitis?

A 
□ Streptococci
□ Staphylococci
□ Enterococci
□ Gram negative bacilli
□ Clostridium
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25
What is type 2 necrotising fasciitis (and what causes it)?
- Monomicrobial | - Normally associated with Strep. pyogenes
26
What are the clinical features of necrotising fasciitis?
- 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
27
How is necrotising fasciitis managed?
- Surgical review is mandatory - Imaging may help but could delay treatment - Antibiotics should be broad spectrum □ Flucloxacillin □ Gentamicin □ Clindamycin
28
What is the mortality of necrotising fasciitis?
- Overall mortality ranges between 17-40%
29
What is pyomyositis?
○ Purulent infection deep within striated muscle, often manifesting as an abscess ○ Infection is often secondary to seeding into damaged muscle ○ Multiple sites involved in 15%
30
What are the common sites for pyomyositis?
- Thigh - Calf - Arms - Gluteal region - Chest wall - Psoas muscle
31
What are the clinical features of pyomyositis?
- Can present with fever, pain and woody induration of affected muscle - If untreated can lead to septic shock and death
32
What are the predisposing factors of pyomyositis?
``` □ Diabetes mellitus □ HIV/immunocompromised □ Intravenous drug use □ Rheumatological diseases □ Malignancy □ Liver cirrhosis ```
33
What are the causes of pyomyositis?
- Commonest cause is Staph aureus | - Other organisms can be involved including Gram positive/negatives, TB and fungi
34
How is pyomyositis managed?
- Investigation using CT/MRI | - Treatment is drainage with antibiotic cover depending on Gram stain and culture results
35
What are the predisposing factors od septic bursitis?
- Infection is often from adjacent skin infection - Other predisposing factors include □ Rheumatoid arthritis □ Alcoholism □ Diabetes mellitus □ Intravenous drug abuse □ Immunosuppression □ Renal insufficiency
36
What are the clinical features of septic bursitis?
- Peribursal cellulitis, swelling and warmth are common - Fever and pain on movement also seen - Diagnosis is based on aspiration of the fluid
37
What causes septic bursitis?
- Most common cause is Staph aureus - Rarer organisms include □ Gram negatives □ Mycobacteria □ Brucella
38
What is infectious tenosynovitis?
○ Infection of the synovial sheaths that surround tendons ○ Flexor muscle-associated tendons and tendon sheaths of the hand most commonly involved ○ Penetrating trauma most common inciting event
39
What causes infectious tenosynovitis?
○ Most common cause Staph aureus and streptococci ○ Chronic infections due to mycobacteria, fungi ○ Possibility of disseminated gonococcal infection
40
What is the clinical presentation of tenosynovitis?
- Present with erythematous fusiform swelling of finger - Held in a semiflexed position - Tenderness over the length of the tendon sheath and pain with extension of finger are classical
41
How is infectious tenosynovitis managed?
- Empiric antibiotics | - Hand surgeon to review ASAP
42
What are toxic mediated syndromes?
○ Often due to superantigens ○ 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
43
What are the causes of toxic mediated syndromes?
``` - Mostly due to some strains of Staphylococcus aureus and Streptococcus pyogenes □ Staph aureus: ® TSST1 ® ETA and ETB □ Strep pyogenes: ® TSST1 ```
44
What are the diagnostic criteria for staphylococcal TSS?
- Fever - Hypotension - Diffuse macular rash - Three of the following organs involved □ Liver, blood, renal, gastrointestinal, CNS, muscular - Isolation of Staph aureus from mucosal or normally sterile sites - Production of TSST1 by isolate - Development of antibody to toxin during convalescence
45
What is the mortality of sptretococcal TSS compared to staphylococcal TSS?
50% (strep) | 5% (staph)
46
What is the treatment of streptococcal associated TSS?
``` -Treatment necessitates urgent surgical debridement of the infected tissues □ Remove offending agent (e.g. tampon) □ Intravenous fluids □ Inotropes □ Antibiotics □ Intravenous immunoglobulins ```
47
What is staphylococcal scalded skin syndrome?
- Infection due to a particular strain of Staph aureus producing the exfoliative toxin A or B (ETA, ETB) - Characterised by widespread bullae and skin exfoliation - Usually occurs in children but rarely in adults as well - Treatment with intravenous fluids and antimicrobials - Mortality 3% in children but higher in adults who often are immunosuppressed
48
What is penton-Valentine leucocidin toxin?
- It is a gamma haemolysin - Can be transferred from one strain of Staph aureus to another, including MRSA - Can cause SSTI and haemorrhagic pneumonia - Tends to affect children and young adults - Patients present with recurrent boils which are difficult to treat - Treat with antibiotics that reduce toxin production
49
What are the risk factors for intravenous-catheter associated infections?
- Continuous infusion >24 hours - Cannula in situ >72 hours - Cannula in lower limb - Patients with neurological/neurosurgical problems
50
What are the causes of intravenous-catheter associated infections?
- Most common organism is Staph aureus (MSSA and MRSA) - Commonly forms a biofilm which then spills into bloodstream - Can seed into other places (e.g. endocarditis, osteomyelitis) - Diagnosis made clinically or by positive blood cultures
51
How are intravenous-catheter associated infections managed?
- Treatment is to remove cannula - Express any pus from the thrombophlebitis - Antibiotics for 14 days - Echocardiogram
52
How are intravenous catheter associated infections prevented?
□ 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
53
What does a class 1 surgical wound mean?
Clean wound (respiratory, alimentary, genital or infected urinary systems not entered)
54
What does a class 2 surgical wound mean?
Clean-contaminated wound (above tracts entered but no unusual contamination)
55
What does a class 3 surgical wound mean?
Contaminated wound (Open, fresh accidental wounds or gross spillage from the gastrointestinal tract)
56
What does a class 4 surgical wound mean?
Infected wound (existing clinical infection, infection present before the operation)
57
What are the causes of surgical wound infections?
- Staph aureus (including MSSA and MRSA) - Coagulase negative Staphylococci - Enterococcus - Escherichia coli - Pseudomonas aeruginosa - Enterobacter - Streptococci - Fungi - Anaerobes
58
What are the aetiologies of surgical wound infecion?
- Diabetes - Smoking - Obesity - Malnutrition - Concurrent steroid use - Colonisation with Staph aureus
59
What procedural factors can lead to surgical wound infections?
- Shaving of site the night prior to procedure - Improper preoperative skin preparation - Improper antimicrobial prophylaxis - Break in sterile technique - Inadequate theatre ventilation - Perioperative hypoxia
60
How are surgical wound infections diagnosed?
- 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 (e.g. bone infection) - Antibiotics to target likely organisms

Infectious disease (13 decks)

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