Cellulitis

Author: Dr Amy Stanway MB ChB, Department of Dermatology, Waikato Hospital. Reviewed and updated by Dr Jannet Gomez, Postgraduate student in Clinical Dermatology, Queen Mary University London, UK, and Chief Editor, Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, July 2016.

What is cellulitis?

Cellulitis is a common bacterial infection of the lower dermis and subcutaneous tissue.  It results in a localised area of red, painful, swollen skin, and systemic symptoms. Similar symptoms are experienced with the more superficial infection, erysipelas, so cellulitis and erysipelas are often considered together.

Who gets cellulitis?

Cellulitis affects people of all ages and races. Predispositions to cellulitis include:

Many people falsely attribute an episode of cellulitis to an unseen spider bite. Documented spider bites have not led to cellulitis. 

What causes cellulitis?

The most common bacteria causing cellulitis are Streptococcus pyogenes (two thirds of cases) and Staphylococcus aureus (one third). Rare causes of cellulitis include: 

What are the clinical features of cellulitis?

Cellulitis can affect any site, most often a limb

The first sign of the illness is often feeling unwell, with fever, chills and shakes (rigors). This is due to bacteria in the blood stream (bacteraemia). Systemic symptoms are soon followed by development of a localised area of painful, red, swollen skin. Other signs include:

Cellulitis may be associated with lymphangiitis and lymphadenitis, which are due to bacteria within lymph vessels and local lymph glands. A red line tracks from the site of infection to nearby tender, swollen lymph glands.

After successful treatment, the skin may flake or peel off as it heals. This can be itchy.

What are the complications of cellulitis?

Severe or rapidly progressive cellulitis may lead to:

Sepsis is recognised by fever, malaise, loss of appetite, nausea, lethargy, headache, aching muscles and joints. Serious infection leads to hypotension (low blood pressure, collapse), reduced capillary circulation, heart failure, diarrhoea, gastrointestinal bleeding, renal failure and loss of consciousness. 

How is the diagnosis made?

The diagnosis of cellulitis is primarily based on the clinical features. Investigations may reveal:

Imaging may be performed. For example:

What is the differential diagnosis of cellulitis?

Cellulitis is often diagnosed when another inflammatory skin disease is actually responsible for redness and swelling. Conditions causing "pseudocellulitis" include: 

 

What is the treatment for cellulitis?

Cellulitis is potentially serious. The patient should rest and elevate the affected limb. The edge of the involved area of swelling should be marked to monitor progression/regression of the infection.

Knowledge of local organisms and resistance patterns is essential in selecting appropriate antibiotics. The management of cellulitis is becoming more complicated due to rising rates of methicillin-resistant Staphylococcus aureus (MRSA) and macrolide- or erythromycin-resistant Streptococcus pyogenes.

Treatment of uncomplicated cellulitis

If there are no signs of systemic illness or extensive cellulitis, patients can be treated with oral antibiotics at home, for a minimum of 5–10 days. In some cases, antibiotics are continued until all signs of infection have cleared (redness, pain and swelling), sometimes for several months. Treatment should also include:

Treatment of cellulitis with systemic illness

More severe cellulitis and systemic symptoms should be treated with fluids, intravenous antibiotics and oxygen. The choice of antibiotics depends on local protocols based on prevalent organisms and their resistance patterns, and may be altered according to culture/susceptibility reports.

Sometimes oral probenecid is added to maintain antibiotic levels in the blood.

Treatment may be switched to oral antibiotics when fever has settled, cellulitis has regressed, and CRP is reducing.

Multidisciplinary care

What is the management of recurrent cellulitis?

Patients with recurrent cellulitis should:

Patients with 2 or more episodes of cellulitis may benefit from chronic suppressive antibiotic treatment with low-dose penicillin V orerythromycin, for one to two years.

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