Cellulitis is a bacterial infection of the deeper skin and the fat under it, most often caused by streptococci or Staphylococcus aureus. Bacteria get in through a break in the skin, such as a cut, a bite, an ulcer or cracked skin between the toes.
Key symptoms
- Red, warm, swollen and painful patch of skin, usually on one leg
- Redness that spreads over hours to days
- Fever, chills or feeling unwell
- A nearby wound, insect bite, ulcer or athlete's foot
What you find on exam
- Redness with blurred edges; mark the border with a pen to track spread
- Warmth and tenderness; a soft, fluctuant area suggests an abscess
- Tender swollen lymph nodes and red streaks toward them
- Vital signs to look for sepsis
- Look for the entry point, including between the toes
Tests
- Usually a clinical diagnosis; mild cases need no tests
- Blood count, CRP and blood cultures if the patient looks sick
- Ultrasound if an abscess is suspected; culture any pus
- Duplex ultrasound if a leg blood clot is possible
Treatment basics
- Mild: an oral antibiotic that covers streptococci, such as cephalexin
- Add MRSA coverage (doxycycline or trimethoprim-sulfamethoxazole) if there is pus or MRSA risk
- Severe: IV cefazolin, or vancomycin if MRSA is likely
- Raise the limb, drain any abscess, treat the skin problem that let bacteria in
- Usually 5 days of antibiotics, longer if improvement is slow
Red flags
- Pain much worse than the skin looks, dusky skin, blisters or crackling (necrotizing infection)
- Signs of sepsis: fever, fast heart rate, low blood pressure
- Spread despite 48 hours of antibiotics, or infection around the eye
Practice it in Making Synapses
Making Synapses cases
Related guides
Sources: NCCPA PANCE Content Blueprint; NBOME COMLEX-USA clinical presentations; AAMC Core Entrustable Professional Activities (Core EPAs). Written by Making Synapses. Making Synapses is not affiliated with these organizations.