Erysipelas

Part of a spectrum of infection.

1. Impetigo - see http://adultemergencymedicine.blogspot.com/2018/08/rashes-impetigo.html 

2. Erysipelas is a superficial cellulitis, with similar risk factors. It looks a lot worse than cellulitis with ruptured bullae and vivid bright red erythema. Almost all erysipelas is caused by group A beta haemolytic strep. It can recur due to persistence of risk factors and lymphatic drainage. Complications can include abscesses, gangrene, chronic leg swelling

Signs and symptoms are normally abrupt, affecting predominantly the lower limb and face. It has a sharp raised border, and is bright red and swollen. The swelling may lead to dimpling, blistering, and even necrosis.

3. Cellulitis
Cellulitis is very rarely bilateral. 35-50% of patients will have a leukocytosis, 60-92% will have an elevated ESR, and 75-95% will have an elevated CRP.  Blood cultures are unlikely to be helpful.
Orals are very bioavailable so most of the time are just as good as IVs.

Often caused by strep and staph. Atypicals are common: Cat bites can have pasteurella, sea water Vibrio vulnificus, fresh water Aeromonas hydrophila, fish farms Streptococcus iniae. These atypicals can cause a rapidly progressive cellulitis.

Fascitis necrotizante

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Class I: No signs of systemic toxicity or co-morbidities. Can be managed on POs.
Class II: 2 or more SIRS, but no organ dysfunction, or have a co-morbidity. May need IV outpatient management.
Class III: Sepsis and organ dysfunction, or unstable co-morbidities normally require admission.
Class IV: Severe life threatening infection.

4. Necrotising Fascitis

https://www.dermnetnz.org/topics/erysipelas/
https://journalfeed.org/article-a-day/2018/lrinec-score-physical-exam-or-imaging-for-necrotizing-infection
http://www.emdocs.net/cellulitis-mimics-ed-considerations/
https://first10em.com/cellulitis-antibiotics/
https://www.rcemlearning.co.uk/modules/cellulitis-and-other-skin-infections/
https://journalfeed.org/article-a-day/2018/is-a-blood-culture-needed-in-cellulitis
https://www.rcemlearning.co.uk/references/cellulitis/
http://www.tamingthesru.com/blog/2018/9/3/necrotizing-fasciitis-and-the-spectrum-of-soft-tissue-infections