Editing Skin infections

== '''Definitions:''' ==

* '''Cellulitis''' involves deeper dermis and subcutaneous tissue. Can get petechiae, ecchymosis, bullae. Indistinct borders. Beta-haemolytic strep and stap aureus - see below for a table of other organisms based on inoculating mechanism.
* '''Erysipelas''' involves upper dermis and epidermis - clear demarcation on skin, often raised edges, more rapid onset, brighter red appearance. Involvement of the ear is a distinguishing feature of erysipelas - no deeper dermal tissue. Mostly caused by beta-haemolytic strep.
* '''Skin abscess''' is a collection of pus within dermis or subcutaneous tissue
* '''Furuncle''' (boil) is a deep infection of a hair follicle
* '''Carbuncle''' is a collection of multiple coalesced furuncles. Commonly seen on back, axila, buttocks

== '''Differential diagnosis''' ==

* Necrotizing fasciitis - rapidly-progressive erythema or pain out of proportion to exam findings
* Toxic shock syndrome
* Clostridial myonecrosis

== '''Complications''' ==

* Bacteraemia
* Endocarditis
* Metastatic infection 
* Sepsis
* Toxic shock syndrome
* Septic arthritis or OM

== '''Principles of management:''' ==

* Antibiotics
** Treat for cellulitis whenever you are uncertain whether it is cellulitis or erysipelas
** Indications for MRSA coverage
*** Systemic toxicity
*** Cellulitis with purulent wound drainage
*** Known MRSA colonisation or infection
*** Injection drug use
*** High-risk neutropaenia
** Regimens: 
*** No MRSA factors: cefazolin/cefalexin
*** MRSA factors: Bactrim OR Augmentin DF + doxycycline 100mg BD. Generally avoid clindamycin due to C diff risk and MRSA resistance.
*** MRSA and needs IV: vancomycin
*** Erysipelas can generally be managed as an outpatient: Augmentin DF, cefalexin, or as above if risk of MRSA
* Symptomatic improvement usually within 24-48 hours, but skin manifestations can take longer. Look for reductions in pain, fever, brightness of erythema, and WCC. Skin can begin to weep, blister, or crack as cellulitis evolves - not generally a marker of worsening infection
* Consider decolonisation for MRSA carriers
* Surgery
** Excision of boil/carbuncle and primary closure - be careful not to spill pus into the wound - incise an ellipse to the extent of the skin changes, then tunnel the subcutaneous resection slightly outwards to ensure you don't go into the cavity


== Bacteriology ==
{| class="wikitable"
|'''Exposure'''
|'''Pathogen'''
|-
|Most common pathogens (regardless of exposure)
|
** Group A ''Streptococcus'' (ie, ''Streptococcus pyogenes'')
** Non-group A, beta-hemolytic streptococci (groups B, C, G, and F)
** ''Staphylococcus aureus'' (''S. aureus'')
|-
|Cirrhosis
|
** Gram-negative bacilli:
** ''Klebsiella'' spp
** ''Escherichia coli''
** ''Vibrio vulnificus'' and ''Vibrio parahaemolyticus''*
** ''Aeromonas'' spp*
|-
|Splenic or humoral immune dysfunction
|
** Encapsulated bacteria:
** ''Streptococcus pneumoniae''
** ''Haemophilus influenzae''
|-
|Neutropenia
|
** ''Pseudomonas aeruginosa'' and other Gram-negative bacilli
** ''Clostridium'' spp
** Invasive fungal infections
|-
|Fresh water (lakes, rivers)
|
** ''Aeromonas hydrophila''
** ''Plesiomonas shigelloides''
** ''Edwardsiella tarda''
** ''Pseudomonas aeruginosa''
** ''Shewanella'' spp
|-
|Salt water
|
** ''Vibrio vulnificus'' and ''Vibrio parahaemolyticus''
** ''Erysipelothrix rhusiopathiae''
|-
|Shellfish ingestion, especially oysters
|
** ''Vibrio vulnificus'' and ''Vibrio parahaemolyticus''
|-
|Animal bite
|
** ''See separate topic 'bites'''
|-
|Human bite
|
** ''See separate topic 'bites'''
|-
|Traumatic wound contaminated by soil
|
** ''Clostridium'' spp
** ''Pseudomonas aeruginosa'' and other Gram-negative bacilli
** Fungi (eg, mucormycosis)
|-
|Nail puncture through sneakers
|
** ''Pseudomonas aeruginosa''
|-
|Recent travel
|
** Depends on the location of travel
|}
[[Category:Skin, soft tissue and wounds]]
[[Category:Intern education]]