Etiology

The most common causative agents are Group A beta-hemolytic streptococcus (eg Streptococcus pyogenes)

Staphylococcus aureus

Haemophilus influenzae type B and Staphylococcus pneumoniae (Commonly isolated in paediatric facial cellulitis)

In immunocompromised individuals, Pseudomonas, Proteus, Serratia, Enterobacter, Citrobacter), anaerobes, and others (eg, Helicobacter cinaedi, Fusarium species) are common causative agents. Although rarely fungi (eg, Cryptococcus) and herpes simplex virus may also be involved.

In hospital acquired cellulitis group A beta-hemolytic Streptococcus [GABHS] or Clostridium perfringens are commonly isolated.