Microbial invasion of the layers of the skin and underlying soft tissues.

The FDA defines acute bacterial skin and skin structure infection (ABSSSI) as a bacterial infection of the skin with a lesion size area of at least 75 cm2 (cellulitis, erysipelas, wound infection, major cutaneous abscess).

The EMA classification of bacterial skin and soft tissue infection (BSSTI) includes cellulitis, erysipelas, wound infections (traumatic or post-surgical) and major abscesses.

Complicated skin and soft tissue infections (cSSTI) are the most severe and involve deeper soft tissue. Staphylococcus aureus is the most common cause of cSSTIs, with methicillin-resistant S. aureus (MRSA) being a particular challenge.