Cellulitis
Cellulitis is a bacterial skin infection affecting deeper skin layers, treated per the IDSA 2014 Skin and Soft Tissue Infection guideline.
Symptoms
Expanding red, warm, swollen, tender skin, usually on the lower legs with poorly defined borders; fever, chills, and red streaking may occur.
Causes and risk
Streptococcus and Staphylococcus bacteria enter through breaks in the skin; risk factors include lymphedema, obesity, prior cellulitis, diabetes, and athlete's foot.
How it is evaluated
Diagnosis is clinical -- routine cultures are not needed for typical cases, per the IDSA guideline, which reserves blood and tissue cultures for high-risk presentations. Marking the borders of redness helps track whether it's spreading or improving.
Treatment
Oral antibiotics for 5 days are first-line for uncomplicated cases, with MRSA coverage added when indicated, per the IDSA guideline; more severe cases with systemic signs of illness may need IV antibiotics. Close follow-up within 48-72 hours confirms the infection is responding.
When to seek care
Pain that is out of proportion to how the skin looks, rapid spreading, purple or blackened skin, blood-filled blisters, numbness, or a crackling sensation under the skin (crepitus) are red flags for necrotizing fasciitis -- a surgical emergency, per the NEJM review of necrotizing soft-tissue infections. Notably, early necrotizing fasciitis can look like ordinary cellulitis, so the absence of these signs does not fully rule it out.