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Cellulitis is caused by bacterial infection of the dermis layer of the skin and the deeper subcutaneous tissues. Often the infection is due to a break or puncture to the skin which allows bacteria to enter, however in some cases no obvious break to skin integrity can be located.

The most common sites for cellulitis to occur are the legs and face, although cellulitis can cause infection to any area of skin. Typically the presentation is of unilateral leg symptoms following a break to the skin.

Cellulitis infections are often minor requiring primary care management, however in elderly patients or those with significant co-morbidities, cellulitis can be of great morbidity and mortality.


Very common infection presenting to primary, secondary and emergency care

Incidence of 24.6/1000

Risk Factors



Most common causative organisms are:

  • Group A beta-haemolytic streptococci – Streptococcus pyogenes
  • Staphylococcus aureus

Less commonly:

  • Streptococcus pneumonia
  • Haemophilus influenza – Often in infants prior to Hib vaccination
  • Gram negative bacilli
  • Anaerobes



  • Often in the lower limbs, effecting one leg
  • Symptoms spread quickly
  • Erythema (rubor) – blends into surrounding skin. “Tracking” can occur along blood vessels and tends to spread more quickly than generalised erythema
  • Pain (dolor)
  • Swelling (tumor)
  • Warmth of effected skin (calor)
  • Often a site of skin damage – ulcer, wound, bite mark, injection site
  • Systemic effects – fever, malaise, nausea, rigors, confusion in the elderly
Left Leg Cellulitis
Left Leg Cellulitis. Image from Wikimedia Commons. Courtesy Colm Anderson
An example of 'tracking' cellulitis secondary to an open wound
An example of ‘tracking’ cellulitis secondary to an open wound. Image from wikimedia commons. Author: James Heilman, MD


  • DVT
  • Varicose eczema
  • Ruptured Baker’s cyst
  • Necrotizing fasciitis
  • Metastatic cancer (carcinoma erysipeloides)


Primary Care

Not usually required

Diagnosis can be made on clinical history and examination alone

If there is an obvious wound in the skin with discharge then this may be swabbed

Secondary Care

Bloods – Raised WCC, CRP, fasting glucose, lipids, cholesterol

Blood cultures  – Identify the causative organism and direct antibiotic choice

X-ray, CT, MRI – If concerns of deeper infection and/or foreign body in situ


General considerations:

Send to hospital if:

  • Significantly unwell with symptoms such as tachycardia, tachypnoea, hypotension, vomiting, or acute confusion
  • Unstable co-morbidities such as uncontrolled diabetes
  • Contaminated wound
  • Limb threatening infection due to vascular compromise
  • Sepsis or life threatening complications such as necrotizing fasciitis
  • Very young (<1 years) or frail
  • Immunocompromised
  • Gross limb swelling
  • Facial cellulitis
  • Periorbital cellulitis


If minor/mild cellulitis and is being treated by GP:

PO Flucloxacillin 500mg QDS for 7 days

Or if penicillin allergic

PO Erythromycin 500 QDS or Clarithromycin 500 mg BD for 7 days


For cases requiring management in hospital:

Flucloxacillin 1 gram QDS IV (For 48 hours, then r/v if can be stepped down to oral)

Or if penicillin allergic

Clindamycin 600mg QDS IV (For 48 hours, then r/v if can be stepped down to oral)

If case may have been contaminated by fresh or salt water consult microbiology




  • Abscess formation
  • Sepsis
  • Myositis / Osteomyelitis
  • Necrotizing fasciitis – consider if pain is not being eased by analgesia!!
  • If around the eye can spread to cause meningitis
  • Post streptococcal nephritis



  • Persistent leg ulceration
  • Chronic lymphoedema



Vast majority of patients will make a complete and uncomplicated recovery

Recurrence rates of cellulitis have been reported between 11-16%


  • Murtagh’s General Practice. 6th Ed. (2015) John Murtagh, Jill Rosenblatt
  • Oxford Handbook of General Practice. 3rd Ed. (2010) Simon, C., Everitt, H., van Drop, F.
  • Beers, MH., Porter RS., Jones, TV., Kaplan JL., Berkwits, M. The Merck Manual of Diagnosis and Therapy

Read more about our sources

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Dr Tom Leach

Dr Tom Leach MBChB DCH EMCert(ACEM) FRACGP currently works as a GP and an Emergency Department CMO in Australia. He is also a Clinical Associate Lecturer at the Australian National University, and is studying for a Masters of Sports Medicine at the University of Queensland. After graduating from his medical degree at the University of Manchester in 2011, Tom completed his Foundation Training at Bolton Royal Hospital, before moving to Australia in 2013. He started almostadoctor whilst a third year medical student in 2009. Read full bio

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