Infections Flashcards
Examples of skin infections
Cellulitis
Necrotising fasciitis
Pathophysiology of cellulitis
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.
*Aetiology of cellulitis
Mostly thought to be Streptococci pyogenes but possibly gram negative organisms, anaerobes or fungi can cause it.
*Clinical presentation of cellulitis
Erythema in the involved area (usually lower extremity) with poorly demarcated margins, swelling, warmth and tenderness.
Erysipelas: Raised and well demarcated.
What is Erysipelas
Essentially the superficial form of cellulitis, affecting upper dermis and superficial lymphatics
Diagnosis of cellulitis
Usually clinical
Culture possible
Treatment of cellulitis
Rest
Analgesia
Elevate limb
*Empirical antibiotics
Complications of cellulitis
Abscess formation (needs aspiration and drainage) Gangrene
What is cellulitis
Poorly demarcated infection of the dermis and subcutaneous tissue
What is necrotising fasciitis
Necrotising infection involving any layer of the deep soft tissue and fascia
Pathophysiology of necrotising fasciitis
Deep seating infection of the subcutaneous tissue results in a fulminant and spreading destruction of the fascia and fat.
Initially, skin may be required.
Clinical presentation of necrotising fasciitis
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.
Epidemiology of necrotising fasciitis
500 cases a year (uncommon)
*Types of necrotising fasciitis
Type 1 - Polymicrobial infection
Type 2 - Group A Streptococcus
Type 3 - Gram-negative monomicrobial infection
Type 4 - Fungal infection
Aetiology of Type 1 Necrotising fasciitis
Polymicrobial infection:
Aerobic and anaerobic bacteria
Usually in immunocompromised or chronic disease
Usually follows surgery or in diabetics
Aetiology of Type 2 Necrotising fasciitis
Group A Streptococcus:
usually otherwise well patients
Aetiology of Type 3 Necrotising fasciitis
Gram-negative mono microbial infection:
Includes marine organisms such as Vibrio spp and Aeromonas hydrophil
These occur if wound exposed to seawater
Aetiology of Type 4 Necrotising fasciitis
Zygomycetes after traumatic wounds or burns.
Necrotising fasciitis diagnosis
Clinical
Bedside finger test: Probing in a 2cm incision with index finger
Necrotising fasciitis treatment
Early debridement of the affected tissue
IV broad spectrum antibiotics
Necrotising fasciitis complications
Significant mortality rate
Septic shock
*Cellulitis is generally caused by Streptococcus pyogenes. Describe how you would identify
Gram film Streptococcus = gram positive cocci in chains Blood agar Beta-haemolytic = Complete haemolysis Lancefield test Group A = Strep pyogenes
