Infections

Question 1

Examples of skin infections

Answer 1

Cellulitis

Necrotising fasciitis

Question 2

Pathophysiology of cellulitis

Answer 2

Usually follows a breach in the skin.
In some cases no obvious portal, but may be microscopic.
Once organisms enter into the subcutaneous tissue they colonise and multiply.
Can lead to blistering, abscesses and ulceration.

Question 3

*Aetiology of cellulitis

Answer 3

Mostly thought to be Streptococci pyogenes but possibly gram negative organisms, anaerobes or fungi can cause it.

Question 4

*Clinical presentation of cellulitis

Answer 4

Erythema in the involved area (usually lower extremity) with poorly demarcated margins, swelling, warmth and tenderness.
Erysipelas: Raised and well demarcated.

Question 5

What is Erysipelas

Answer 5

Essentially the superficial form of cellulitis, affecting upper dermis and superficial lymphatics

Question 6

Diagnosis of cellulitis

Answer 6

Usually clinical

Culture possible

Question 7

Treatment of cellulitis

Answer 7

Rest
Analgesia
Elevate limb
*Empirical antibiotics

Question 8

Complications of cellulitis

Answer 8

Abscess formation (needs aspiration and drainage)
Gangrene

Question 9

What is cellulitis

Answer 9

Poorly demarcated infection of the dermis and subcutaneous tissue

Question 10

What is necrotising fasciitis

Answer 10

Necrotising infection involving any layer of the deep soft tissue and fascia

Question 11

Pathophysiology of necrotising fasciitis

Answer 11

Deep seating infection of the subcutaneous tissue results in a fulminant and spreading destruction of the fascia and fat.
Initially, skin may be required.

Question 12

Clinical presentation of necrotising fasciitis

Answer 12

Mimics cellulitis.
Important early signs: Pain, tenderness and systemic illness out of proportion to physical signs.
Bullae and ecchymotic skin lesions.
Spreading erythema, underlying crepitus and systemic toxicity.

Question 13

Epidemiology of necrotising fasciitis

Answer 13

500 cases a year (uncommon)

Question 14

*Types of necrotising fasciitis

Answer 14

Type 1 - Polymicrobial infection
Type 2 - Group A Streptococcus
Type 3 - Gram-negative monomicrobial infection
Type 4 - Fungal infection

Question 15

Aetiology of Type 1 Necrotising fasciitis

Answer 15

Polymicrobial infection:
Aerobic and anaerobic bacteria
Usually in immunocompromised or chronic disease
Usually follows surgery or in diabetics

Question 16

Aetiology of Type 2 Necrotising fasciitis

Answer 16

Group A Streptococcus:

usually otherwise well patients

Question 17

Aetiology of Type 3 Necrotising fasciitis

Answer 17

Gram-negative mono microbial infection:
Includes marine organisms such as Vibrio spp and Aeromonas hydrophil
These occur if wound exposed to seawater

Question 18

Aetiology of Type 4 Necrotising fasciitis

Answer 18

Zygomycetes after traumatic wounds or burns.

Question 19

Necrotising fasciitis diagnosis

Answer 19

Clinical

Bedside finger test: Probing in a 2cm incision with index finger

Question 20

Necrotising fasciitis treatment

Answer 20

Early debridement of the affected tissue

IV broad spectrum antibiotics

Question 21

Necrotising fasciitis complications

Answer 21

Significant mortality rate

Septic shock

Question 22

*Cellulitis is generally caused by Streptococcus pyogenes. Describe how you would identify

Answer 22

Gram film
Streptococcus = gram positive cocci in chains
Blood agar
Beta-haemolytic = Complete haemolysis
Lancefield test
Group A = Strep pyogenes