Aetiology of cellulitis and erysipelas
Beta-haemolytic streptococci (including Streptococcus pyogenes [group A streptococcus (GAS)], Streptococcus dysgalactiae subspecies equisimilus [group C/G streptococcus], Streptococcus agalactiae [group B streptococcus (GBS)]) are the most common causes of nonpurulent, recurrent cellulitis and erysipelas (eg associated with lymphoedema).
Cellulitis caused by Staphylococcus aureus (including methicillin-resistant strains [MRSA]) is less frequent and is often associated with penetrating trauma or ulceration. Purulent cellulitis (eg associated with an abscess or boil) is typically caused by S. aureus.
Other pathogens need to be considered in specific circumstances, including:
- patients with chronic liver disease; consider gram-negative bacteria
- patients with immune compromise; consider a broad range of organisms including gram-negative bacteria, fungi and mycobacteria
- patients with infection of a diabetes-related foot ulcer
- infection affecting the face or neck; consider infection of the retropharyngeal area, deep neck space, salivary glands or infection from dental origin
- people who inject drugs who are also at increased risk of methicillin-resistant Staphylococcus aureus (MRSA) infection
- infection associated with an animal or human bite
- infection associated with penetrating injury
- infection of water-immersed wounds (including seawater, fresh water, brackish water, aquarium water, and soil- or sewage-contaminated water)
- presence of a foreign body.