cellulitis

Last edited 07/2021 and last reviewed 08/2023

Cellulitis describes a deep infection of connective tissue, usually skin and subcutaneous tissues, in which there is obvious oedema. Erysipelas is a form of cellulitis

• some authors state that Group A beta haemolytic streptococcus (Streptococcus pyogenes) is the major cause of celluluitis (1) whereas others state that cellulitis is most frequently caused by Streptococcus pyogenes or Staphylococcus aureus (2)
• Stapylococcus aureus is a minor cause of the classic erysipelas (1)
  • Streptococcus pyogenes is the major agent of erysipelas, but also Staphylococcus aureus may be the causative micro-organism
• microbiological spectrum of cellulitis is wider than erysipelas including not only the mentioned staphylococci and streptococci, but also other Gram-positive and Gram-negative micro-organisms, including anaerobic bacteria (3)

Cellulitis presents as a hot, raised, tender area of skin whose margin is less well demarcated than in erysipelas. Often, the patient is systemically unwell with fever and rigors. An abrasion usually allows the infective organism to enter the skin.

Investigations:

• full blood count
• blood cultures
• swab analysis

Treatment is with systemic antibiotics, for example, oral penicillin V plus flucloxacillin (or erythromycin alone) or co-amoxiclav alone. If cellulitis is severe then management may require parenteral benzylpenicillin plus flucloxacillin OR co-amoxiclav alone.

Key points (4):

• exclude other causes of skin redness (inflammatory reactions or non-infectious causes)
• consider marking extent of infection with a single-use surgical marker pen
• offer an antibiotic. Take account of severity, site of infection, risk of uncommon pathogens, any microbiological results and MRSA status
• infection around eyes or nose is more concerning because of serious intracranial complications
• *a longer course (up to 14 days in total) may be needed but skin takes time to return to normal, and full resolution at 5 to 7 days is not expected
• do not routinely offer antibiotics to prevent recurrent cellulitis or erysipelas

Reference:

1. Brook I. Microbiology and management of soft tissue and muscle infections. J. Int. Surgery 2007.
2. Matz H et al.Bacterial infections: uncommon presentations Clinics in Dermatology, Volume 23, Issue 5, September-October 2005, Pages 503-508.
3. Lazzarini L et a.. Erysipelas and cellulitis: clinical and microbiological spectrum in an Italian tertiary care hospital. J. of Infect. 2005; 51 (5):383-389.
4. Public Health England (June 2021). Managing common infections: guidance for primary care